Library

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Diseases of the colon & rectum 39 (1996), S. 935-937 
    ISSN: 1530-0358
    Keywords: Anus/injuries ; Foreign bodies ; Rectum/injuries ; Rectum/surgery ; Human ; Vacuum extraction, obstetric instrumentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract PURPOSE: Rectal foreign bodies can be extracted by non-surgical methods. However, glass objects require technical considerations to minimize morbidity and may necessitate surgical extraction. We describe a technique that allowed safe transanal extraction of a glass foreign body and avoided laparotomy. METHODS: A patient with a history of a previous rectal foreign body that required laparotomy presented with another incarcerated rectal foreign body. After attempts at manual extraction failed, spinal anesthesia was induced, and an obstetric vacuum extractor was used to transanally withdraw the glass foreign body. RESULTS: The glass foreign body was withdrawn uneventfully using the vacuum extractor. Laparotomy was avoided. The patient was hospitalized for observation and discharged 24 hours later. CONCLUSIONS: Use of the delivery vacuum extractor provided a safe, cost-effective method of glass foreign body removal by the transanal route. Literature review found no other reports of rectal foreign body removal by this method.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1435-604X
    Keywords: Photosensitizer ; Photodynamic therapy ; mTHPC ; Temoporfin ; Pharmacokinetics ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract A Phase I photodynamic therapy (PDT) clinical trial was carried out with Temoporfin (Foscan®, mTHPC) at the Departments of Otolaryngology at Orebro Medical Center (OMC) and Long Island Jewish Medical Center (LIJMC). A range of drug doses, consisting of 0.3, 0.15, 0.075 and 0.0375 mg kg−1, were utilized. Light treatment was performed on the sixth day after injection of the photosensitizer mTHPC. Photodynamic therapy was done on prostate cancer (six cases), bronchial cancer (one case), nasopharyngeal cancer (three cases), laryngeal cancer (eight cases), mesothelioma (one case), laryngeal papilloma (five cases) and basal cell nevus syndrome (one case). A number of patients were treated more than once. Plasma was collected and analysed at 1, 24, 48, 72, 96, 120 and 144 h and at 2 weeks post-injection, to follow the loading and clearance rate of the photosensitizer. Normal and malignant tissues were collected immediately prior to PDT, chemically extracted, and analysed for drug content spectrofluorometrically. Plasma drug levels were proportional to the dose. The half-life of the drug was 45.4 h across the entire dose range. The ratio of the drug in the tumour compared to normal adjacent mucosa was in the range of 2–3. There were no significant adverse effects. These data establish the basis for full clinical trials.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1432-1440
    Keywords: Angiotensin receptors types ; Cloning ; Signaling ; Transgenic models ; Regulation ; Transcription ; Organ specificity ; Human ; Cardiovascular ; Receptor antagonists
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The actions of angiotensin II in the cardiovascular system are transmitted by two known and possibly some unknown angiotensin receptor types. AT1 and AT2 both correspond to G-protein-coupled receptors with seven hydrophobic transmembrane domains, several N-glycosylation sites and a potential G-protein binding site. Cloning of coding regions and promoter sequences contributed to the understanding of receptor protein function and regulation. Angiotensin receptors with atypical binding properties for the known AT1- and AT2-specific ligands are expressed on human cardiac fibroblasts and in the human uterus. In several animal models, receptors with high affinity for angiotensin (1–7) have been described. AT1 stimulation is mediated by the generation of phospholipid-derived second messengers, activation of protein kinase C, the MAPkinase pathway and of immediate early genes. Recently, phosphorylation and dephosphorylation of tyrosine kinases have been associated with AT1- and AT2-mediated signal transduction. ATR are regulated by phosphorylation, internalization, modification of transcription rate and mRNA stability. Regulation is highly cell and organ specific and includes upregulation of ATR in some pathophysiological situations where the renin angiotensin system is activated. Whereas the function of AT1 in the cardiovascular system is relatively well established, there is little information regarding the role of AT2. Recent hypotheses suggest an antagonism between AT1 and AT2 at the signal transduction and the functional level. Transgenic animal models, particularly with targeted disruption of the AT1 and AT2 genes, suggest the contribution of both genes to blood pressure regulation. Genetic polymorphisms have been described in the AT1 and AT2 gene or neighbored regions and are used to analyze the association between gene defects and cardiovascular diseases. AT1 antagonists are now being introduced into the treatment of hypertension and potentially heart failure, and more interesting pharmacological developments are expected from the ongoing basic studies.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-1440
    Keywords: Key words Angiotensin receptors ; mRNA ; Quantitative PCR ; Human ; Atrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The number of atrial angiotensin II binding sites is reduced in end-stage human heart failure. The goals of our study were the development of a quantitative polymerase chain reaction for angiotensin II receptor type 1 mRNA to determine the angiotensin receptor type1 (AT1) mRNA content in the atria of patients with end-stage heart failure. We established a quantitative PCR based on coamplification of AT1 wild-type and an internal standard in the same PCR, followed by liquid-phase hybridization of PCR products in microtiter plates and quantitation by ELISA. Glyceraldehyde phosphate dehydrogenase mRNA in the same samples was used to relate the AT1 mRNA content to a stably expressed reference gene. Atrial samples from 11 patients with end-stage heart failure obtained at cardiac transplantation were compared with atrial samples from 11 patients with normal cardiac function undergoing routine cardiac surgery. A PCR/ELISA system with a variance of about 6% after reverse transcription and a linear measuring range was established. In the samples from 11 patients with end-stage heart failure a 58% decrease in AT1 mRNA content was found in comparison with 11 controls (heart failure: 185680±196912 AT1 mRNA copies/μg RNA, controls: 440555±268456, P〈0.02). When AT1 mRNA content was related to glyceraldehyde phosphate dehydrogenase mRNA, a 65% decrease was detected (AT1/glyceraldehyde phosphate dehydrogenase: heart failure: 4.84±5.18; controls: 13.74±7.77; P〈0.005). Standardization of PCR resulting in a low coefficient of variance, high reproducibility, and large sample capacity is possible using optimal internal standardization and the liquid-phase hybridization/ELISA system for detection. The optimized PCR procedure indicated downregulation of atrial AT1 in end-stage human heart failure, suggesting a reduced capacity of the atria to respond to angiotensin II stimulation in end-stage heart failure.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1432-1440
    Keywords: Angiotensin receptors ; mRNA ; Quantitative PCR ; Human ; Atrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The number of atrial angiotensin II binding sites is reduced in end-stage human heart failure. The goals of our study were the development of a quantitative polymerase chain reaction for angiotensin II receptor type 1 mRNA to determine the angiotensin receptor typel (AT1) mRNA content in the atria of patients with end-stage heart failure. We established a quantitative PCR based on coamplification of AT1 wild-type and an internal standard in the same PCR, followed by liquidphase hybridization of PCR products in microtiter plates and quantitation by ELISA. Glyceraldehyde phosphate dehydrogenase mRNA in the same samples was used to relate the AT1 mRNA content to a stably expressed reference gene. Atrial samples from 11 patients with endstage heart failure obtained at cardiac transplantation were compared with atrial samples from 11 patients with normal cardiac function undergoing routine cardiac surgery. A PCR/ELISA system with a variance of about 6% after reverse transcription and a linear measuring range was established. In the samples from 11 patients with end-stage heart failure a 58% decrease in AT1 mRNA content was found in comparison with 11 controls (heart failure: 185680±196912 AT1 mRNA copies/μg RNA, controls: 440555±268456, P〈0.02). When AT1 mRNA content was related to glyceraldehyde phosphate dehydrogenase mRNA, a 65% decrease was detected (AT1/glyceraldehyde phosphate dehydrogenase: heart failure: 4.84±5.18; controls: 13.74±7.77; P〈0.005). Standardization of PCR resulting in a low coefficient of varince, high reproducibility, and large sample capacity is possible using optimal internal standardization and the liquid-phase hybridization/ELISA system for detection. The optimized PCR procedure indicated downregulation of atrial AT1 in end-stage human heart failure, suggesting a reduced capacity of the atria to respond to angiotensin II stimulation in end-stage heart failure.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1432-1912
    Keywords: Key words Rabbit ; Human ; 5-HT1Dα receptor structure ; 5-HT1Dβ receptor structure ; Radioligand binding ; Ketanserin ; Methiothepin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The study of serotonin receptor function has been complicated by the extreme molecular diversity of serotonin receptor subtypes, the lack of selective agonists and antagonists for many of the subtypes, and divergence in the pharmacological properties of a single receptor subtype across different animal species. An example of this pharmacological diversity between species homologues is provided by the 5-HT1D receptor subfamily. To further advance the ability to characterize and pharmacologically compare functional responses mediated by native 5-HT1D receptors, we have cloned the 5-HT1Dα and 5-HT1Dβ receptor subtypes from the rabbit and evaluated their pharmacological profiles using radioligand binding assays. The deduced amino acid sequences of the rabbit 5-HT1Dα and 5-HT1Dβ receptor genes displayed 60% overall identity [75% transmembrane (TM) identity] to each other and 〉90% overall identity (95% TM identity) to their corresponding human homologues. Two compounds were identified in binding assays which discriminated between the closely-related 5-HT1D receptors. Ketanserin exhibited high affinity (pKi=7.66) and selectivity (〉20-fold) for the 5-HT1Dα receptor while methiothepin displayed high affinity (pKi=7.86) and selectivity (16-fold) for the 5-HT1Dβ receptor subtype. The rabbit and human recombinant 5-HT1D receptors showed significant intraspecies (rabbit 5-HT1Dα vs. 5-HT1Dβ) and interspecies (i.e. rabbit vs. human 5-HT1Dα) similarities in their ligand binding profiles. These data suggest that 5-HT1D-mediated responses in rabbit preparations may provide information relevant to the pharmacology of the 5-HT1D receptor subtypes in humans.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 354 (1996), S. 765-772 
    ISSN: 1432-1912
    Keywords: Key words Albino rabbit ; Pigmented rabbit ; Human ; Iris dilator ; α-Adrenoceptor subtype ; Imidazolines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The relative potency of α-adrenoceptor agonists and the dissociation constants of competitive antagonists were studied to characterize the post-junctional α-adrenoceptor of the human iris dilator muscle. The data obtained from human iris dilator tissue was compared to that from rabbit. The iris dilator muscle was mounted in an organ bath and tension changes were recorded. (–)-Norepinephrine, (–)-phenylephrine (PE), oxymetazoline and p-aminoclonidine caused contractile responses in albino rabbit, pigmented rabbit and human iris dilator muscle in a concentration-dependent manner. The imidazoline molecules were partial agonists. In rabbit iris dilator, desensitization occurred to repeated oxymetazoline application at an interval of 1 h but recovery to the agonist activity was complete in about 3 h. Exposure to cocaine (10 μmol/l), hydrocortisone (100 μmol/l) and U-0521, a catechol-O-methyltransferase inhibitor (100 μmol/l), significantly potentiated the response to norepinephrine by 92-, 32- and 7 fold in iris dilator tissue of albino rabbit, pigmented rabbit and human, respectively. After block of „uptake1” and „uptake2”, the EC50 values of norepinephrine in the albino rabbit, pigmented rabbit and human iris dilator did not differ and ranged from 99 to 195 nmol/l. Small but significant potentiation by uptake blockers was also observed in the responses to PE in the albino rabbit or pigmented rabbit iris dilator. The average maximum tension induced by 100 μmol/l PE was 96 ± 11 mg (n =10), 197 ± 11 mg (n = 11), 45 ± 5 mg (n = 27) in albino rabbit, pigmented rabbit and human iris dilator, respectively. In human iris dilator, the responses to PE were competitively antagonized by prazosin, 5-methylurapidil and phentolamine with apparent pK B values of 7.3, 6.6 and 7.5, respectively. The pK B values of the prazosin-PE interaction in iris dilator of albino and pigmented rabbit were 8.6 and 6.4, respectively. These results suggest that the post-junctional α-adrenoceptors in iris dilator may be similar to that in pigmented rabbit iris. The α-adrenoceptor of the human or pigmented rabbit iris dilator may be characterized as α1L-adrenoceptor subtype. The α-adrenoceptor of albino rabbit iris dilator appears to be a high affinity subtype. Furthermore, albino rabbit may not be the best strain for the drug research which is relevant to human ocular therapeutics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1432-0843
    Keywords: Key words Hydroxyurea ; Pharmacokinetics ; Toxicity ; Human ; Drug therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  A group of 18 patients with advanced cancer were entered on a phase I study of a 120-h continuous intravenous infusion of hydroxyurea. The dose of hydroxyurea was escalated in cohorts of patients from 1 to 2 to 3.2 g/m2 per day. The primary dose-limiting toxicity was neutropenia, often accompanied by leukopenia, thrombocytopenia and generalized skin rash. Prophylactic treatment of patients with dexamethasone and diphenhydramine hydrochloride prevented the skin rash, but not the hematopoietic toxicities. The pharmacokinetics of hydroxyurea were studied in all patients. The steady-state concentrations of hydroxyurea were linearly correlated with the dose (R 2 = 0.71, n = 18, P〈0.0001). The mean±SE concentrations were 93±16, 230±6 and 302±27 μM at 1, 2 and 3.2 g/m2 per day, respectively. The mean±SE renal and nonrenal clearances of hydroxyurea were 2.14±0.18 and 3.39±0.28 l/h per m2 (n = 16), neither of which correlated with the dose. The concentration of hydroxyurea in plasma decayed monoexponentially with a mean±SE half-life of 3.25±0.18 h (n = 17). The steady-state concentration of hydroxyurea was 〉200 μM in all nine patients treated at 2 g/m2 per day, a dose which was well tolerated for 5 days. We recommend this dose for phase II trials in combination with other antineoplastic agents.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Pediatric surgery international 11 (1996), S. 33-40 
    ISSN: 1437-9813
    Keywords: Immunohistochemistry ; Human ; Vasoactive intestinal polypeptide ; Somatostatin ; Neuropeptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The pathophysiology of the impaired sphincter function in Hirschsprung's disease is still unclear. The peptidergic innervation of the aganglionic large intestine is known to be disturbed. The present study analyzes the peptidergic innervation of the aganglionic internal anal sphincter (IAS) in comparison with that of the circular layer of ganglionic and aganglionic large intestine. Immunoreactivity for the following substances was analyzed: vasoactive intestinal polypeptide (VIP), substance P (SP), met-enkephalin (ENK), calcitonin gene-related peptide (CGRP), somatostatin (SOM), and neuropeptide Y (NPY). All patients were operated upon with Soave's endorectal pull-through technique and a posterior partial myectomy of the IAS. For comparison, specimens of resected IAS from adult patients operated upon for rectal cancer as well as autopsy specimens from a 2-year-old child were analyzed. Differences in the density of nerve fibers between the ganglionic and aganglionic large intestine were in accordance with previous studies. In sections of normoganglionic IAS moderately dense networks of nerve fibers immunoreactive for NPY, SOM, and VIP were observed. The occurrence of NPY and SOM was somewhat more frequent here compared to the colonic circular muscle coat, whereas the opposite was seen for VIP. In aganglionic IAS abundant nerve fibers immunoreactive for NPY, SOM, and VIP were observed. Only a few SP-, CGRP-, and ENK-immunoreactive fibers were found in normal and aganglionic IAS. It is concluded that there were moderate differences in the peptidergic innervation of the aganglionic IAS as compared to the normal ganglionic IAS and the circular muscle coat of the ganglionic and aganglionic large intestine.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Skeletal radiology 25 (1996), S. 563-567 
    ISSN: 1432-2161
    Keywords: Key words Radiography ; Human ; Hand ; Fracture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Objective. A commercially available positioning device was evaluated to assess whether standardized positioning of hand radiographs for the pronated oblique view was facilitated. Design and subjects. One hundred hands of volunteers were radiographed in postero-anterior, antero-posterior and pronated oblique projections, with and without use of the positioning device, and with and without application of a plaster cast. Results. The variation in pronation angle in the uncovered hand was 6° with, and 24° without the positioning device. Use of the device diminished intra- and inter-positioning variation by 14° and 18° respectively. A plaster cast led to a variation of up to 26°, despite use of the device. Conclusions. Use of the positioning device improved consistency for the pronated oblique radiograph. There was no improvement with a cast on the forearm.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 11
    ISSN: 1432-2307
    Keywords: Bax ; Bcl-2 ; Apoptosis ; Central nervous system ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Bax and Bcl-2 proteins are identified as regulating molecules for programmed cell death. In the central nervous system, programmed cell death or apoptosis is considered to be an important phenomenon that is related to neuron vulnerability to a variety of toxic effects, including ischaemic insult. In this study, localization of Bax and Bcl-2 proteins was investigated in the human central nervous system using autopsy cases without any neurological disorder. Results were compared with findings in the rat. Most neurons in human cerebral cortex, basal ganglia and brain stem were positive for both Bax and Bcl-2 proteins, whereas Purkinje cells in cerebellum and neurons in hippocampal CA1, CA2 and CA3 regions were positive for Bax but negative or weakly positive for Bcl-2. Glial cells examined in all sections were negative for both proteins. Choroid plexus, ependymal cells and arachnoid villi showed positive reactivity for both proteins. A possible relationship between the localization of Bax or Bcl-2 proteins and the cell vulnerability in central nervous system is discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 12
    ISSN: 1432-0533
    Keywords: Key wordsβ-Amyloid precursor protein ; Ubiquitin ; Human ; Spinal cord ; Trauma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We evaluated by immunohistochemistry the presence of β-amyloid precursor protein (ßAPP) and ubiquitin-like material which may accumulate in axons of the human spinal cord subjected to injury. Autopsy material was obtained from nine cases with different types of trauma: breech delivery with neonatal spinal injury, compression of the cord induced by fractures of the vertebral column, haematomas or intradural meningioma. The post-trauma period ranged from 10 days to several years. The spinal cord of six control cases without evidence of injury presented βAPP immunoreactivity in nerve cell bodies and in a few axonal profiles but not in dendrites. Seven of the nine cases with spinal cord trauma showed an accumulation of βAPP-immunoreactive material in axons of the longitudinal tracts at the site of the injury. Five cases presented similar axonal immunoreactivity in the grey matter of the cord. Ubiquitin-like immunoreactivity was present in expanded axons in cases with spinal cord injury. Cases with spinal cord trauma thus present βAPP-immunoreactive axons particularly of the longitudinal tracts in the same way as in trauma to rat spinal cord and in various brain injuries. The aggregation of βAPP-immunoreactive material indicates disturbed axonal transport of βAPP. Accumulation of ubiquitin-like immunoreactive material in expanded axons at the site of trauma may be one prerequisite for degradation of abnormal proteins by the ubiquitin-mediated proteolytic pathway.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 13
    ISSN: 1432-0568
    Keywords: Testis ; Myoid cells ; Fetus ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Testicular peritubular cells are located in the lamina propria of seminiferous tubules. These cells, significantly contributing to the basal membrane of seminiferous epithelium, have been studied in a number of species. However, there is a lack of data on the development of the lamina propria in the human testis. The aim of our survey was to investigate the characteristics of the lamina propria and, in particular, peritubular cells in the fetal human testes by immunohistological and stereological methods. Therefore, testes (14–39 weeks of gestation, n=45) were dissected and fixed in a 4% buffered paraformaldehyde solution. Several pieces of each testis were embedded in paraffin and processed for immunohistochemical and stereological analysis. All investigated testes have shown sex cords in the process of development and differentiation. Morphologically, peritubular cells in the lamina propria can be divided into two types: fibroblast-like (FL) and myoid-like (ML) type (cells which much resemble mature myoid cells). By immunohistochemistry, both FL and ML cells are found to be strongly positive for the intermediate filament desmin, but negative for α-smooth actin. While FL cells intensively express Ki-67 demonstrating proliferative activity, ML cells are found to be negative. The basement membrane of sex cords as well as the blood vessels of the interstitium show strong positivity to collagen IV and laminin. Concerning the correlation between the appearance of the investigated antigens with the gestational age, all antigens have been expressed (in the manner described above) already in the 14th week of gestation. The stereological analysis of the number (Nv) and volume (Vv) of peritubular cells indicates a pulsatile development of these cells in the lamina propria of the human fetal testis. While the stereological variables determined for FL cells show a gradual decrease, the same variables determined for ML cells demonstrate a successive increase. It appears that the lamina propria of the fetal human testes shares many of the properties previously discovered in rodents.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 91 (1996), S. 409-415 
    ISSN: 1432-0533
    Keywords: Key words Nerve growth factor ; Low-affinity nerve ; growth factor receptor ; Phosphoprotein B-50/ ; neuromodulin ; Immunohistochemistry ; Human ; skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Phosphoprotein B-50, also termed neuromodulin or growth-associated protein GAP43, is a membrane-bound molecule expressed in neurons. It is particularly abundant during periods of axonal outgrowth in development and regeneration of the central and peripheral nervous systems. Recently it was reported that B-50 plays a role in the growth morphology of regenerating muscle fibers. Moreover, in vitro studies have demonstrated that the expression of B-50 in the pheochromocytoma PC12 cells can be stimulated by the nerve growth factor (NGF). Expression of the low-affinity nerve growth factor receptor (LNGFR) during muscle regeneration has also been reported. Here, we studied the expression of NGF, LNGFR and B-50 in myopathy. To investigate the state of regeneration, we examined serial sections stained to demonstrate neural cell adhesion molecule and desmin. Light microscopy showed that muscle fiber regeneration in idiopathic inflammatory myopathy corresponds closely to NGF, LNGFR and B-50 immunoreactivity. The coexpression of phosphoprotein B-50, NGF and LNGFR in regenerating muscle fiber corroborates the assumption that in muscle there is a trophic pathway concerning phosphorylation or de novo synthesis of B-50 by the NGF via the LNGFR. In conclusion, a simultaneous expression of NGF, LNGFR and B-50 in muscles plays a role in the growth morphology of regenerating muscle fibers.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 15
    ISSN: 1432-0533
    Keywords: Key words Asymptomatic ; Cytokines ; Human ; immunodeficiency virus ; Major histocompatibility ; complex class II ; Polymerase chain reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Among the various mechanisms proposed to explain the pathogenesis of cerebral lesions in human immunodeficiency virus (HIV)-induced encephalitis, a cytokine-mediated action has found most favour. Indeed, elevated expression of cytokines such as interleukin (IL)-1 and tumour necrosis factor-α (TNF-α), thought to be neurotoxic, has been found in AIDS patients. As a previous study had demonstrated the presence of HIV proviral DNA in brain tissue of a number of HIV-positive non-AIDS patients, we undertook this present investigation using morphological, immunohistochemistry (IHC) and polymerase chain reaction (PCR) methods to detect the expression of major histocompatibility complex (MHC) class II molecules, the presence of HIV-1 proviral DNA and of the cytokines TNF-α, IL-1α, IL-4 and IL-6 in brains of the same group of individuals. The study included brains of 36 asymptomatic HIV-1 positive patients and the results were compared with those of AIDS patients either affected by HIV encephalitis (n = 8) or exempt from any neuropathological changes (n = 10) as well as of normal controls (n = 5). Results show that: HIV proviral DNA could be detected by PCR in 17 out of the 36 brains from HIV-positive pre-AIDS cases; most (15 of 17) of PCR-positive brains showed minimal to severe expression of MHC class II antigen; and cytokines could be detected predominantly within white matter even at this early stage. The data demonstrated that the state of immune activation described in AIDS is already present at the pre-AIDS stage and suggest that the presence of cytokines may already trigger the cascade of events leading to brain damage.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 92 (1996), S. 525-527 
    ISSN: 1432-0533
    Keywords: Key words Mercury ; Human ; Neurotoxicity ; Cortical ; motor neuron ; Amyotrophic lateral sclerosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A 24-year-old man injected himself intravenously with metallic mercury in a suicide attempt, and died 5 months later after cutting his wrists. The brain was removed at postmortem and 7-μm paraffin sections were cut from representative blocks. Dense deposits of mercury were found on autometallography in large cortical motor neurons, but in no other cerebral neurons. Smaller mercury deposits were found in the brain stem (in the mesencephalic trigeminal nucleus, noradrenergic neurons, and in neurons for extraocular muscles), the cerebellum (in the dentate nucleus) and in lateral motor neurons in the C2/3 spinal cord. Mercury deposits were found in glial cells in all regions. The finding that elemental mercury enters human cortical motor neurons in preference to other cerebral neurons raises the possibility that this neurotoxin may play a part in the pathogenesis of some human motor neuron diseases.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 17
    ISSN: 1432-0568
    Keywords: trk neurotrophin-receptor proteins ; p75 protein ; Paravertebral-sympathetic ganglia ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We investigated the expression of immunoreactivity (IR) for low- (p75) and high-affinity (trk proteins) neurotrophin-receptor proteins in adult human paravertebral-sympathetic ganglion neurons. Mouse monoclonal antibodies against the pan-neurotrophin-receptor p75, and rabbit polyclonal antibodies against specific epitopes of the intracytoplasmic domain on trk neurotrophin-receptor proteins were used in fresh unfixed and formaldehyde-fixed paraffin-embedded sympathetic ganglia. All adult human paravertebral-sympathetic neurons displayed trkA neurotrophin-receptor-like protein IR, 10% express trkC neurotrophin-receptor-like protein IR, 37–44% show p75 IR, and no IR was obtained for trkB neurotrophin-receptor-like protein. The intensity of immunostaining was independent of the neuron size. Labelling of non-neuronal tissues, especially blood-vessel walls, was observed for p75, trkA and trkC neurotrophin-receptor proteins. These results indicate that overlapping exists in the expression of p75 and trk neurotrophin-receptor proteins in adult human paravertebral-sympathetic neurons, and suggest that neurotrophins might act on these neurons.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 194 (1996), S. 439-444 
    ISSN: 1432-0568
    Keywords: Human ; Embryogenesis ; Three-dimensional reconstruction ; Computer-assisted design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Three-dimensional computer graphic reconstructions of four human embryos at Carnegie stages 11 to 23 portray the relationships and dimensions of individual organ systems. This paper illustrates the cranial, neural, pharyngeal, gut, vascular and nephric architecture in these developing embryos. This technology can be applied to in situ hybridization and immunohistochemistry to map zones and times of developmental gene activity.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 19
    ISSN: 1432-0533
    Keywords: Key words AIDS ; Apoptosis ; Human ; immunodeficiency virus ; Rabies ; Neuropathology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A 46-year-old man was bitten by a dog in Mali; anti-rabies vaccination was incomplete. Three months later he was admitted to hospital with fever and diarrhea. Human immunodeficiency virus (HIV) serology was positive and CD4 count was 70/mm3. His status worsened rapidly with confusion hydrophobia and hypersialorrhea. Despite anti-rabies serotherapy and vaccination, he died suddenly 12 days after admission. Immunofluorescence on cerebral tissue samples established rabies encephalitis. Neuropathology showed mild encephalitis with occasional Babès nodules and rare perivascular mononuclear cuffs. Intraneuronal Negri inclusion bodies were remarkably diffuse and abundant. They were clearly demonstrated by immunocytochemistry and electron microscopy. Apoptotic neurons were identified in the brain stem and hippocampus in the vicinity of inflammatory foci. In contrast, apoptosis could not be demonstrated in non-inflammatory areas, even where Negri bodies were numerous. There was no associated HIV encephalitis or opportunistic infection. The occurrence of rabies encephalitis in AIDS represents a random association, but is probably not exceptional as rabies is endemic in many countries and the AIDS epidemic is spreading worldwide. In this case, although the incubation duration and clinical presentation were comparable to those in classical rabies, the T-cell-mediated immunosuppression may account for the weak inflammatory reaction and unusually abundant viral multiplication. This observation confirms that all those at risk for rabies, particularly immunocompromised patients, should receive complete anti-rabies treatment including vaccines and specific immunoglobulins, as soon as possible after infection.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 194 (1996), S. 373-378 
    ISSN: 1432-0568
    Keywords: Paravertebral sympathetic ganglia ; Calretinin ; Aging ; Immunoblotting ; Immunohistochemistry ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Calretinin is an “EF-hand” calcium-binding protein involved in the maintenance of intracellular calcium ion homeostasis. This study was understaken to investigate the presence of calretinin in human lumbar paravertebral sympathetic ganglia from subjects of different ages (26–85 years) using immunohistochemical and immunoblotting methods. Calretinin-like immunoreactivity was found in a subpopulation of postganglionic sympathetic neurons, whose percentage decreased progressively with aging by about 50% (63% of immunoreactive neurons at ≤40 years; 29% at ≥81 years) whereas the neuronal density remained basically unchanged. Calretinin-like immunoreactivity showed a granular pattern of cytoplasmic distribution suggesting preferential localization of this protein associated with intracellular membranes. Occasionally diffuse cytosolic labelling was also observed. The immunoblotting demonstrated a protein band with an estimated molecular weight of 30 kDa, approximately. Present results provide, for the first time, evidence for the presence of calretinin in human paravertebral sympathetic ganglia. Since the number of calretinin-like immunoreactive neurons decreased significantly with aging our findings suggest an involvement of this protein in the age-dependent impairment of sympathetic function.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 21
    ISSN: 1432-0533
    Keywords: Key words Varicella-zoster virus ; AIDS ; Human ; immunodeficiency virus ; Vasculitis ; Spinal cord ; infarction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Varicella-zoster virus (VZV) infection is usually benign and self-limited. However, particularly in the immunosuppressed host, serious central nervous system complications may occur, including encephalitis, myelitis, and cerebral vascular occlusion. We report the case of a 57-year-old male with AIDS, who rapidly developed a sixth cranial nerve palsy and progressive myelopathy. There was no antecedent zoster rash. Autopsy revealed VZV ventriculo-encephalitis and vasculitis, as well as a transverse infarction of the spinal cord without evidence of direct infection of the cord parenchyma. Spinal cord infarction secondary to VZV vasculitis is an unusual cause of myelopathy in immunosuppressed patients.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 22
    ISSN: 1432-0568
    Keywords: Epidermal growth factor receptor ; Dorsal root ganglia ; Immunoblotting ; Immunohistochemistry ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Transforming growth factor-α (TGFα) enhances neuronal survival and neurite outgrowth in cultured dorsal root ganglia (DRG) sensory neurons. It binds a membrane protein, denominated epidermal growth factor receptor (EGFr). EGFr has been localized in developing and adult human DRG. However, it remains to be elucidated whether all DRG neurons express EGFr or whether differences exist among neuronal subtypes. This study was undertaken to investigate these topics in adult human DRG using immunoblotting, and combined immunohistochemistry and image analysis techniques. A mouse monoclonal antibody (clone F4) mapping within the intracytoplasmic domain of EGFr was used. Immunoblotting revealed two main proteins with estimated molecular masses of ∼- 65 kDa and 170 kDa, and thus consistent with the full-length EGFr. Additional protein bands were also encountered. Light immunohistochemistry revealed specific immunoreactivity (IR) for EGFr-like proteins in most (86%) primary sensory neurons, the intensity of immunostaining being stronger in the small- and intermediate-sized ones. Furthermore, EGFr-like IR was also observed in the satellite glial cells of the ganglia as well as in the intraganglionic and dorsal root Schwann cells. Taken together, our findings demonstrate that EGFr, and other related proteins containing the epitope labeled with the antibody F4, are responsible for the EGFr IR reported in DRG. Furthermore, we demonstrated heterogeneity in the expression of EGFr-like IR in adult human primary sensory neurons, which suggests different responsiveness to their ligands.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 23
    ISSN: 1432-0568
    Keywords: Embryology ; Temporomandibular joint ; PGP 9.5 ; Innervation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The development of nerve fibres in the temporomandibular joint (TMJ) in relation to the development of bone, muscle and fibre components was investigated in human fetuses ranging from 9 weeks of gestation to birth. Immunohistochemistry for the glia-associated protein S-100 and for the neuro-specific marker protein gene product 9.5 (PGP 9.5) were used; specimens were compared to specimens of adult TMJ capsule and disc. At 9–10 weeks, a small number of neural elements are already present in the connective tissue around the joint and in the mesenchyme between the two articular blastemas from which the disc will differentiate. By 19 weeks many nerve fibres are clearly visible. Immunohistochemical results suggest diffuse disc innervation extending along the entire disc but not in the thin central area. More complex structures, i.e. encapsulated corpuscles, were also seen. The fetal disc appears highly innervated compared to adult tissue; already at this developmental stage morphology and distribution of nerves and corpuscles in the joint capsule are comparable to those in the adult joint. It may be concluded that the innervation of the TMJ is detectable from the end of the second month and that it develops fully between the third and the fifth month of gestation. Nerve endings in the disc are most numerous at 20 weeks, after which a progressive reduction, possibly secondary to the growth of articular tissues, is observed throughout the last trimester of fetal life and into adult life. The innervation of the lateral pterygoid muscle, on the contrary, is much less than that seen in adult muscles, even at full-term.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 24
    ISSN: 1432-069X
    Keywords: Key words Photodynamic therapy ; Cisplatin ; Human ; squamous cell carcinoma cell line ; Apoptosis ; Nuclear ; matrix protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 25
    ISSN: 1432-1238
    Keywords: Closed-loop controlled ventilation ; Human ; Initial settings ; Computer ; Mechanical ventilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective To test a method that allows automatic set-up of the ventilator controls at the onset of ventilation. Design Prospective randomized crossover study. Setting ICUs in one adult and one children's hospital in Switzerland. Patients Thirty intubated stable, critically ill patients (20 adults and 10 children). Interventions The patients were ventilated during two 20-min periods using a modified Hamilton AMADEUS ventilator. During the control period the ventilator settings were chosen immediately prior to the study. During the other period individual settings were automatically determined by the ventilator (AutoInit). Measurements and results Pressure, flow, and instantaneous CO2 concentration were measured at the airway opening. From these measurements, series dead space (V DS), expiratory time constant (RC), tidal volume (V T), total respiratory frequency (f tot), minute ventilation (MV), and maximal and mean airway pressure (P aw, max andP aw, mean) were calculated. Arterial blood gases were analyzed at the end of each period.P aw, max was significantly less with the AutoInit ventilator settings whilef tot was significantly greater (P〈0.05). The other values were not statistically significant. Conclusions The AutoInit ventilator settings, which were automatically derived, were acceptable for all patients for a period of 20 min and were not found to be inferior to the control ventilator settings. This makes the AutoInit method potentially useful as an automatic startup procedure for mechanical ventilation.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 26
    ISSN: 1432-1238
    Keywords: Key words Atrial natriuretic peptide ; Infusion ; Human ; Cardiac surgery ; Renal function ; Acute renal failure ; Inotropic agents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To investigate the effects of IV infusion of atrial natriuretic peptide (human ANP 1–28) on renal function in patients with acute heart failure and renal impairment after cardiac surgery. Design: Pharmocodynamic dose-effect investigation. Setting: Cardiothoracic Intensive Care Unit of a university hospital. Patients: Twelve patients (mean age 68 years, range 44–78 years) treated with inotropic drugs and an intra-aortic balloon pump (n=8) were studied 1–3 days after cardiac surgery. Patients had acute renal impairment, defined as a rise in serum creatinine of more than 50% compared to preoperative values. Patients were receiving dopamine and furosemide infusion to increase urine flow. Interventions: Baseline measurements of glomerular filtration rate (GFR) and renal blood flow (51Cr-EDTA and PAH clearance) were first performed during two 30-min periods. ANP was then administered for two consecutive 30-min periods (25 and 50 ng/kg per min), followed by two control periods. Measurements and main results: Mean arterial pressure decreased by 6% at the highest ANP dose. Urine flow, GFR and RBF increased 62%, 43% and 38%, respectively, while renal vascular resistance decreased 30%. At this dose level, circulating ANP concentrations were on the average eight fold higher than preinfusion levels. Conclusions: ANP improved renal function and decreased elevated renal vascular resistance in patients with renal dysfunction after cardiac surgery. The improvement in renal blood flow and glomerular filtration rate may be of potential therapeutic value to prevent or treat exaggerated renal vasoconstriction in patients with acute renal impairment following cardiac surgery.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 27
    ISSN: 1432-1238
    Keywords: Atrial natriuretic peptide ; Infusion ; Human ; Cardiac surgery ; Renal function ; Acute renal failure ; Inotropic, agents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective To investigate the effects of IV infusion of atrial natriuretic peptide (human ANP 1–28) on renal function in patients with acute heart failure and renal impairment after cardiac surgery. Design Pharmocodynamic, dose-effect investigation. Setting Cardiothoracic Intensive Care Unit of a university hospital. Patients Twelve patients (mean age 68 years, range 44–78 years) treated with inotropic drugs and an intra-aortic balloon pump (n=8) were studied 1–3 days after cardiac surgery. Patients had acute renal impairment, defined as a rise in serum creatinine of more than 50% compared to preoperative values. Patients were receiving dopamine and furosemide infusion to increase urine flow. Interventions Baseline measurements of glomerular filtration rate (GFR) and renal blood flow (51Cr-EDTA and PAH clearance) were first performed during two 30-min periods. ANP was then administered for two consecutive 30-min periods (25 and 50 ng/kg per min), followed by two control periods. Measurements and main results Mean arterial pressure decreased by 6% at the highest ANP dose. Urine flow, GFR and RBF increased 62%, 43% and 38%, respectively, while renal vascular resistance decreased 30%. At this dose level, circulating ANP concentrations were on the average eight fold higher than preinfusion levels. Conclusions ANP improved renal function and decreased elevated renal vascular resistance in patients with renal dysfunction after cardiac surgery. The improvement in renal blood flow and glomerular filtration rate may be of potential therapeutic value to prevent or treat exaggerated renal vasoconstriction in patients with acute renal impairment following cardiac surgery.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 28
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 108 (1996), S. 450-462 
    ISSN: 1432-1106
    Keywords: Spinal cord ; H-reflexes ; Ia afferents ; Reflex pathways ; Homosynaptic depression ; Human ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It was demonstrated that the soleus H-reflex was depressed for more than 10 s following a preceding passive dorsiflexion of the ankle joint. This depression was caused by activation of large-diameter afferents with receptors located in the leg muscles, as an ischaemic block of large-diameter fibres just below the knee joint abolished the depression, whereas a similar block just proximal to the ankle joint was ineffective. The depression of the H-reflex was not caused by changes in motoneuronal excitability, as motor-evoked potentials by magnetic brain stimulation were not depressed by the same passive dorsiflexion. Therefore it was concluded that the long-lasting depression is due to mechanisms acting at presynaptic level. The transmission of the monosynaptic Ia excitation from the femoral nerve to soleus motoneurones was not depressed by the ankle dorsiflexion. The depression thus seems to be confined to those afferents that were activated by the conditioning dorsiflexion. In parallel experiments on decerebrate cats, more invasive methods have complemented the indirect techniques used in the experiments on human subjects. A similar long-lasting depression of triceps surae monosynaptic reflexes was evoked by a preceding conditioning stimulation of the triceps surae Ia afferents. This depression was accompanied by a reduction of the monosynaptic Ia excitatory postsynaptic potential recorded intracellularly in triceps surae motoneurones, but not by changes in the input resistance or membrane potential in the motoneurones. Stimulation of separate branches within the triceps surae nerve demonstrated that the depression is confined to those afferents that were activated by the conditioning stimulus. This long-lasting depression was not accompanied by a dorsal root potential. It is concluded that the long-lasting depression is probably caused by a presynaptic effect, but different from the “classical” GABAergic presynaptic inhibition which is widely distributed among afferent fibres and accompanied by dorsal root potentials. It is more probably related to the phenomenon of a reduced transmitter release from previously activated fibres, i.e. a homosynaptic post-activation depression. The consequences of this post-activation depression for the interpretation of results on spinal mechanisms during voluntary movements in man are discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 29
    ISSN: 1432-1106
    Keywords: Posture ; Spindle group II afferents ; Crossed pathways ; EMG ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract During upright stance, foot dorsiflexion induced by the movement of a supporting platform elicits a short-(SLR) and a medium-latency response (MLR) in both the soleus and the flexor digitorum brevis muscles; foot plantarflexion elicits a MLR in the tibialis anterior. The SLR is the counterpart of the stretch reflex, but no general agreement exists about the origin of the MLR, though recent results suggest that it is transmitted through group II afferent fibres. Animal studies have shown that group II fibres impinge on interneurones projecting contralaterally as well as ipsilaterally, whereas group I fibres impinge on interneurones which project mainly ipsilaterally. Therefore, we compared the changes in amplitude and latency of the SLRs and MLRs in the right and left limb during postural perturbations induced while subjects maintained both feet on the platform (both-on condition) or while they maintained only one foot on the platform and the other on firm ground (one-on condition). Under the both-on condition, the pattern of EMG responses described above occurred bilaterally. Under the one-on condition, both SLRs and MLRs occurred in the displaced leg. However, whereas the SLRs did not change in amplitude compared with the both-on condition, the MLRs decreased in amplitude to about 50%. MLRs were also present in the non-displaced leg. They were not preceded by any SLR but showed a further decrease in size with respect to the corresponding responses in the perturbed leg. Latency of the MLRs of the perturbed leg increased by about 5 ms passing from the both-on to the one-on condition. In the latter condition, a further increase of 5 ms was observed in the nonperturbed leg with respect to the displaced one. The occurrence of the MLRs but not of the SLRs in the contralateral non-displaced leg is in keeping with the notion that crossed neural pathways fed by spindle group II afferent fibres subserve the MLRs. The changes in latency of the MLRs under the one-on condition compared with both-on give a cue about the synaptic delays along the neural circuit and the time taken by the afferent impulses to cross the spinal cord.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 30
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 127-135 
    ISSN: 1432-1106
    Keywords: Transcranial magnetic brain stimulation ; Motor cortex excitability ; Lorazepam ; Benzodiazepine ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of the short-acting benzodiazepine lorazepam on motor cortex excitability was investigated in 11 healthy volunteers using the technique of focal transcranial magnetic stimulation. The threshold intensity for evoking an electromyographic response in the resting and active abductor digiti minimi muscle, the size of the motor evoked potential, the duration of the cortical and peripheral silent periods, the corticocortical inhibition and facilitation after paired magnetic stimuli, and the transcallosal inhibition were used as parameters to assess various aspects of motor system excitability. Baseline values were compared with data obtained 2, 5 and 24 h after a single oral dose of 2.5 mg lorazepam. Resting and active motor thresholds and the size of the motor evoked potential remained unchanged. The duration of the cortical silent period was prolonged with a maximum effect 5 h after drug intake, while the peripheral silent period did not show any lengthening at that time. The corticocortical inhibition showed a tendency toward more inhibition, while the corticocortical facilitation was almost completely suppressed. The transcallosal inhibition showed an inconsistent trend to less inhibition. In parallel to the pharmacokinetics of lorazepam, all effects peaked at 2 h and 5 h, and were (partially) reversible after 24 h. It is hypothesized that most of these findings are due to the reinforcement of GABA action by lorazepam at the level of the motor cortex. The lack of effect on motor threshold and on the size of the motor evoked potential may indicate that these parameters are physiologically distinct from corticocortical excitability and the cortical silent period. The relevance of the present data in clinical epileptology is discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 31
    ISSN: 1432-1106
    Keywords: Deafferentation ; Proprioception ; Reaching ; Target localization ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This experiment investigated the relative extent to which different signals from the visuo-oculomotor system are used to improve accuracy of arm movements. Different visuo-oculomotor conditions were used to produce various retinal and extraretinal signals leading to a similar target amplitude: (a) fixating a central target while pointing to a peripheral visual target, (b) tracking a target through smooth pursuit movement and then pointing to the target when its excursion ceased, and (c) pointing to a target reached previously by a saccadic eye movement. The experiment was performed with a deafferented subject and control subjects. For the deafferented patient, the absence of proprioception prevented any comparison between internal representations of target and limb (through proprioception) positions during the arm movement. The deafferented patient's endpoint therefore provided a good estimate of the accuracy of the target coordinates used by the arm motor system. The deafferented subject showed relatively good accuracy by producing a saccade prior to the pointing, but large overshooting in the fixation condition and undershooting in the pursuit condition. The results suggest that the deafferented subject does use oculomotor signals to program arm movement and that signals associated with fast movements of the eyes are better for pointing accuracy than slow ramp movements. The inaccuracy of the deafferented subject when no eye movement is allowed (the condition in which the controls were the most accurate) suggests that, in this condition, a proprioceptive map is involved in which both the target and the arm are represented.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 32
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 457-466 
    ISSN: 1432-1106
    Keywords: Eye-head coordination ; Reaction time ; Gaze ; Ocular ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Gaze shifts vary in the extent of eye and head contribution; a large amplitude and/or an eccentric ocular orbital starting position alter the participation of head movement in the shift. The interval between eye onset and head onset determines compensatory counterrolling before and after the shift and the extent of vestibular ocular reflex reduction during the shift. The latency of eye saccades in the head-fixed condition was measured with respect to target amplitude and orbital position in order to establish base-line operations of these two variables as they apply to the headfree condition. Eye movements were measured during single-step saccades in nine young adult humans. The target step, hereafter called a jump, started from three possible fixation lights; e.g., rightward saccades started from the midline (0°) or from -20 or -40° left of the midline, with a maximum amplitude of 80°. The latency of saccades starting from the primary position increased with jump amplitude (amplitude-latency relation). When the eye started eccentrically, the latency was decreased (orbital position-latency relation), with the largest jump amplitudes most affected. These changes can be related to active eye-head coordination. Thus, with a leftward maximal orbital eccentricity, compensatory eye rotation would be impossible with a rightward head movement; however, incorporating the orbital position-latency relation, the forward ocular saccade is expedited by 90 ms. Conversely, with a primary starting position, the ocular component of an 80° gaze saccade could be slowed 125 ms by incorporating the amplitude-latency relation, thus facilitating a head contribution to the gaze shift. The orbital position and amplitude-latency relations were prominent in those subjects with habitually large head contributions to the gaze shift and minimal in individuals with typically small head contributions.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 33
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 483-494 
    ISSN: 1432-1106
    Keywords: Movement organisation ; Movement control ; Spring perturbation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The discrepancy between traditional (force scaling models) and the more recently conceived dynamic explanations of load compensation (λ model) was the departure point for the present study. By using the complex “open” motor skill of catching a ball rather than the traditional “closed” skills under “normal” (baseline) conditions and under conditions where a spring load was applied to the catching hand (thereby changing the dynamics of the skeleto-muscular system) it was hoped to provide further clarification of this issue. Traditional force scaling models, in this respect, would predict that maximal closing velocity of the grasp action, and movement time would not be significantly different between a control and a spring-load condition. In contrast, a dynamic system perspective would maintain that spring loading would be compensated for by a change in the rate of shift of the reciprocal command (R-command). The obtained results showed a significant difference for conditions with regard to the maximal closing velocity of the grasp action, the baseline condition being higher than the two spring-load conditions. Furthermore, a significant difference was found for the aperture at moment of catch, the aperture at moment of catch being smaller in the baseline condition than that under the two springload conditions. With regard to the temporal variables, no significant differences were obtained. A comprehensive overall explanation of the obtained data in terms of the force scaling models was not realisable. It may be that findings supporting such theories are task specific and that for constrained tasks such as catching a ball-different underlying organisational principles apply. The λ model, however, could explain adequately the obtained results. It was concluded that, except for the preparatory phase associated with load compensation before the onset of the movement of the ball, the spatiotemporal structure of the control pattern underlying catching remains the same (invariant) in both baseline and load conditions. Thereby, the spatiotemporal structure of the resulting movement changes under the influence of the load and thus is not the same for load and baseline condition.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 34
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 507-512 
    ISSN: 1432-1106
    Keywords: Saccade ; Express saccade ; Antisaccade ; Attention ; Fixation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In a gap paradigm, where the saccadic reaction times are usually short, the number of express saccades can be further increased and their latency decreased when a valid transient peripheral cue is given 100 ms before target occurrence. In the present study we measured the saccadic reaction times of seven human subjects who had been instructed to make antisaccades (saccades to the side opposite to stimulus presentation) in the gap paradigm. In the first experiment, we presented a 100% valid cue with 100 ms cue lead time. To explore whether the cue reduced the reaction times of the antisaccades, the cue was always presented on the opposite side to where the stimulus occurred (stimulus direction was randomized between 4° to the left and right), and it was thus indicated in each trial to which side the antisaccade was required (procue). In the second set of experiments the cue was consistently presented on either the left or the right side in two different blocks; it was thus noninformative with respect to the direction of the antisaccade. In the first experiment, a significant increase in mean reaction times of correct antisaccades and a considerable increase in erratic prosaccades to the stimulus were obtained compared with a control session with no cue. In the two experimental blocks with noninformative cues, the reaction times of correct antisaccades were decreased when cue and stimulus were on at the same side, while large numbers of erratic prosaccades were again obtained when cue and stimulus were presented on opposite sides. These results suggest that the orienting mechanism elicited by a transient peripheral cue relates to the command and to the decision to make a proversus an antisaccade. Since the subjects reported that they could not prevent, or, moreover, in some cases did not even realize that they were making erratic prosaccades, we conclude that this orienting mechanism occurs automatically, being largely beyond voluntary control.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 35
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 110 (1996), S. 99-110 
    ISSN: 1432-1106
    Keywords: Voluntary movement ; Coordination dynamics ; Stability ; Index finger ; Forearm ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Four right-handed subjects performed rhythmic flexion and extension movements of the index finger in time with an auditory metronome. On each block of trials the forearm of the response hand was placed in a prone, neutral or supine position. In the flex-on-the-beat condition, subjects were instructed to coordinate maximum excursion in the direction of finger flexion with each beat of the metronome. In the extend-on-the-beat condition, subjects were instructed to coordinate maximum excursion in the direction of finger extension with each beat of the metronome. The frequency of the metronome was increased from 1.75 Hz to 3.50 Hz in eight steps (8-s plateaus) of 0.25 Hz. During trials prepared in the extend-on-the-beat pattern, abrupt transitions to either a flex-on-the-beat pattern or to phase wandering often occurred, particularly at higher pacing frequencies. In marked constrast, during trials prepared in the flexon-the-beat pattern such transitions were never present. Both the frequency and the alacrity of these transitions were greater when the forearm was in a prone or neutral position than when the forearm was in a supine position. These results are discussed with reference to the constraints imposed on the coordination dynamics by the intrinsic properties of the neuromuscular-skeletal system.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 36
    ISSN: 1432-1106
    Keywords: Grip force ; Friction ; Motor control ; Gravity ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Humans preserve grasp stability by automatically regulating the grip forces when loads are applied tangentially to the grip surfaces of a manipulandum held in a precision grip. The effects of the direction of the load force in relation to the palm, trunk, and gravity were investigated in blindfolded subjects. Controlled, tangential load-forces were delivered in an unpredictable manner to the grip surface in contact with the index finger either in the distal and proximal directions (away from and toward the palm) or in the ulnar and radial directions (transverse to the palm). The hand was oriented in: (1) a standard position, with the forearm extended horizontally and anteriorly in intermediate pronosupination; (2) an inverted position, reversing the direction of radial and ulnar loads in relation to gravity; and (3) a horizontally rotated position, in which distal loads were directed toward the trunk. The amplitude of the grip-force responses (perpendicular to the grip surface) varied with the direction of load in a manner reflecting frictional anisotropies at the digit-object interface; that is, the subjects automatically scaled the grip responses to provide similar safety margins against frictional slips. For all hand positions, the time from onset of load increase to start of the gripforce increase was shorter for distal loads, which tended to pull the object out of the hand, than for proximal loads. Furthermore, this latency was shorter for loads in the direction of gravity, regardless of hand position. Thus, shorter latencies were observed when frictional forces alone opposed the load, while longer latencies occurred when gravity also opposed the load or when the more proximal parts of the digits and palm were positioned in the path of the load. These latency effects were due to different processing delays in the central nervous system and may reflect the preparation of a default response in certain critical directions. The response to loads in other directions would incur delays required to implement a new frictional scaling and a different muscle activation pattern to counteract the load forces. We conclude that load direction, referenced to gravity and to the hand's geometry, represents intrinsic task variables in the automatic processes that maintain a stable grasp on objects subjected to unpredictable load forces. In contrast, the grip-force safety margin against frictional slips did not vary systematically with respect to these task variables. Instead, the magnitude of the grip-force responses varied across load direction and hand orientation according to frictional differences providing similar safety margins supporting grasp stability.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 37
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 110 (1996), S. 248-264 
    ISSN: 1432-1106
    Keywords: Stiffness ; Impedance ; Stability ; Posture ; Motor control ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The stiffness that is measured at the hand of a multijoint arm emerges from the combined effects of the elastic properties of the muscles and joints, the geometry of the linkages and muscle attachments, and the neural control circuits that act on the arm. The effective stiffness of a nonlinear linkage such as a two-joint arm depends on the force acting on the system as well as the intrinsic stiffness of the actuators. This paper presents an analysis of the factors that affect limb stiffness, including the effects of external forces. Three potential strategies for controlling the stability of the limb are proposed and demonstrated by computer simulations. The predictions from the simulations are then compared experimentally with measured stiffness values for human subjects working against an external force. These experiments were directed toward understanding what strategies are used by the CNS to control limb stiffness and stability. The experimental evidence showed that human subjects must increase the stiffness at the joints in order to maintain limb stability in the presence of applied external forces at the hand. In the process we identified a precise role for muscles which span two or more joints in the control of overall limb stiffness. A local strategy may be used to achieve limb stability, in which the muscle stiffness increases with muscle force. Multijoint muscles are shown to provide mechanical couplings which are necessary for the maintenance of stability. By utilizing these muscles, the neuro-musculo-skeletal system can control a global property of the system (stability) with a passive local strategy.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 38
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 110 (1996), S. 289-297 
    ISSN: 1432-1106
    Keywords: Muscular and cutaneous afferents ; Fall ; Compensatory reactions ; Stepping ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of lower limb deafferentation were examined during execution of a balance recovery step following a forward fall induced by release of an initial inclined posture. The subjects were healthy control subjects and patients with a unilateral loss of the Achilles tendon reflex following S1 radiculitis. Deafferentation of healthy subjects was obtained by unilateral leg ischemia (four subjects) and by foot anesthesia (five subjects). The balance recovery step was characterized by the surface electromyographic (EMG) activity of right and left soleus and tibialis anterior muscles and the kinetics of the center of gravity and center of foot pressure. Experimentally induced and pathological deafferentation decreased the EMG activity of the ipsilateral soleus and lowered the vertical ground reaction force. The lower limb motor activity was more affected by loss of muscle proprioceptive afferents than by loss of plantar cutaneous afferents. Patients showed early and bilateral changes in soleus and tibialis activities, whichever side was affected. The step length of patients was also shorter than that of controls, but it remained similar before and after deafferentation in the healthy subjects. The results are discussed in terms of ipsilateral and crossed pathway connections and functional adaptive strategies.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 39
    ISSN: 1432-1106
    Keywords: Ocular torsion ; Vestibulo-ocular reflex ; Linear vestibulo-ocular reflex ; Ocular counterroll ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We measured human ocular torsion (OT) monocularly (using video) and binocularly (using search coils) while sinusoidally accelerating (0.7 g) five human subjects along an earth-horizontal axis at five frequencies (0.35, 0.4, 0.5, 0.75, and 1.0 Hz). The compensatory nature of OT was investigated by changing the relative orientation of the dynamic (linear acceleration) and static (gravitational) cues. Four subject orientations were investigated: (1) Y-upright — acceleration along the interaural (y) axis while upright; (2) Y-supine — acceleration along the y-axis while supine; (3) Z-RED — acceleration along the dorsoventral (z) axis with right ear down; (4) Z-supine — acceleration along the z-axis while supine. Linear acceleration in the Y-upright, Y-supine and Z-RED orientations elicited conjugate OT. The smaller response in the Z-supine orientation appeared disconjugate. The amplitude of the response decreased and the phase lag increased with increasing frequency for each orientation. This frequency dependence does not match the frequency response of the regular or irregular afferent otolith neurons; therefore the response dynamics cannot be explained by simple peripheral mechanisms. The Y-upright responses were larger than the Y-supine responses (P〈0.05). This difference indicates that OT must be more complicated than a simple low-pass filtered response to interaural shear force, since the dynamic shear force along the interaural axis was identical in these two orientations. The Y-supine responses were, in turn, larger than the Z-RED responses (P〈0.01). Interestingly, the vector sum of the Y-supine responses plus Z-RED responses was not significantly different (P=0.99) from the Y-upright responses. This suggests that, in this frequency range, the conjugate OT response during Y-upright stimulation might be composed of two components: (1) a response to shear force along the y-axis (as in Y-supine stimulation), and (2) a response to roll tilt of gravitoinertial force (as in Z-RED stimulation).
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 40
    ISSN: 1432-1106
    Keywords: Proprioception ; Kinesthesia ; Somatosensory evoked potentials ; Muscle afferent ; Generator sources ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Brisk passive flexion of the proximal interphalangeal joint of the middle finger, produced by using a newly devised instrument, elicited evoked potentials on the scalp. The present study carefully excluded the possible contribution of sensory modalities other than proprioception. The initial part of cortical response was a positive deflexion at the contralateral central area (P1 at 34.6 ms after the stimulus). This was followed by a midfrontal negative wave (N1 at 44.8 ms) and a clear positivity at the contralateral centroparietal area (P2 at 48.0 ms). The evoked responses persisted in spite of the abolition of cutaneous and joint afferents of the finger caused by ischemic anesthesia, but they were lost by ischemic anesthesia of the forearm. Thus, the cortical evoked responses obtained in this study most probably reflect muscle afferent inputs. The scalp distribution of P1 suggested that its cortical generator source was different from that of the N20-P20 components of evoked potentials to electrical median nerve stimulation. Brodmann areas 2 and 3a of human brain, which are known to receive deep receptor inputs, are the most plausible generator sites for the early components of the proprioception-related evoked responses. The amplitude of P2 was related to the velocity but not to the magnitude of movement. In conclusion, the present study established a method for recording the evoked responses to the brisk passive movement of the finger joint, which mainly reflect the dynamic aspects of proprioception mediated through muscle afferent.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 41
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 271-282 
    ISSN: 1432-1106
    Keywords: Balance ; Locomotion ; Motion parallax ; Postural control and sway ; Vision ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Three experiments tested the hypothesis that postural sway during locomotion is visually regulated by motion parallax as well as optical expansion. Oscillating displays of three-dimensional scenes were presented to participants walking on a treadmill, while postural sway was recorded. Displays simulated: (a) a cloud, in which parallax and expansion are congruent, (b) a hallway, (c) the side walls of the hallway, (d) a ground surface, (e) a wall, (f) the wall with a central hole, (g) a hall farther from the observer, and (h) a wall farther from the observer. In contrast to previous results with a hallway, responses with the cloud were isotropic and directionally specific. The other displays demonstrated that motion parallax was more effective than simple horizontal flow in eliciting lateral sway. These results are consistent with the hypothesis that adaptive control of sway during walking is based on congruent expansion and parallax in natural environments.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 42
    ISSN: 1432-1106
    Keywords: Viually-induced gamma-band responses ; Coherency ; Evolutionary spectra ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Visual presentation of an object produces firing patterns in cell assemblies representing the features of the object. Based on theoretical considerations and animal experiments, it has been suggested that the binding of neuronal representations of the various features is achieved through synchronization of the oscillatory firing patterns. The present study demonstrates that stimulus-induced gamma-band responses can be recorded non-invasively from human subjects attending to a single moving bar. This finding indicates the synchronization of oscillatory activity in a large group of cortical neurons. Gamma-band responses were not as apparent in the presence of two independently moving stimuli, suggesting that the neuronal activity patterns of different objects are not synchronized. These results open a new paradigm for investigating the mechanisms of feature binding and association building in relation to subjective perception.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 43
    ISSN: 1432-1106
    Keywords: Pavlovian conditioning ; Slow potentials ; Event-related potentials ; Gamma-band activity ; Skin conductance ; Motor conditioning ; Cholinergic modulation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We examined slow potentials, transient event-related potentials, and oscillatory-like responses in the electroencephalogram during aversive conditioning in humans, in order to determine what is happening in the neocortex when behavioral adaptations are learned. Pictures of an angry and a happy human face served as rein-forced (CS+) and unreinforced (CS-) conditioned stimu li, respectively, in one group, and either the reversed condition or two discriminably different neutral faces in two other groups (total n=48 subjects). The unconditioned stimulus (US) was intracutaneous shock delivered to the left hand 5 s after CS+ onset. The electroencephalographic (EEG) activity was recorded from Fz, Cz, Pz, C3, and C4, electromyographic (EMG) activity from bilateral forearm and corrugator muscles, and skin conductance from the right hand. During acquisition a negative slow potential developed after CS+ (not CS-), which was more pronounced when a neutral face served as CS+. Early (iCNV, initial contingent negative variation) and late (tCNV, terminal contingent negative variation) components of the slow-potential response were positively related to the magnitude of conditioned EMG responses. Differentiation of tCNV was larger when neutral faces signaled the US; iCNV persisted during extinction when a happy face served as CS+. Late-occurring event-related potentials (ERPs) elicited by the US diminished over conditioning, whereas short-latency US components and ERPs elicited by CS events did not. Fourier analysis revealed oscillatory (“gamma-band”) activity between 30 and 40 Hz, which persisted up to 3 s after US delivery and diminished as conditioning progressed. Our findings indicate that learning is expressed in neocortical structures at the earliest stages of conditioning. The functional roles of the three types of EEG response in learning are discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 44
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 112 (1996), S. 485-495 
    ISSN: 1432-1106
    Keywords: Proprioception ; Joint position sense ; Signal detection theory ; Models ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This report describes two models of human behavior when detecting displacements of joints that allow one to compare and integrate findings from different proprioception tests in a quantitative way. Results from various tests have led to different and often conflicting conclusions about proprioceptive behaviors and their underlying neural mechanisms. However, it has been impossible to compare data and conclusions in any meaningful way due to lack of a suitable analytical framework to accommodate important differences in procedures used in the various tests. These models can provide one such framework. The models, developed using data from proprioception tests reported in the literature, describe how the amplitude and velocity of joint excursions, and the subject bias expressed as false alarm rate, affect the detectability of displacements of joints. Two models were needed to represent observed behaviors: one based on velocity signals alone (the velocity model) and the other based on both velocity and positional signals (the displacement-velocity model). To simulate the detection-decision process subjects used to determine whether a joint was displaced, we adapted strategies from signal detection theory. The models characterized reported behaviors from disparate proprioception tests remarkably well, requiring only 3 degrees of freedom in the velocity case, and 4 in the displacement-velocity case.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 45
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 107 (1996), S. 486-496 
    ISSN: 1432-1106
    Keywords: Periodontal afferent ; Mechanoreceptor ; Biting ; Sensorimotor control ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The force exerted by the central incisors while holding and splitting a food morsel was analyzed to characterize human biting behavior. The force was continuously sampled by a transducer-equipped plate upon which a small piece of dry biscuit or half a peanut rested. Subjects were instructed to position the plate between the incisor teeth and to split the morsel either immediately (“split task”) or after holding it for a brief period (“hold-and-split task”). While holding either food substance between the incisors, subjects automatically exerted light contact forces of less than 1 N (0.36–0.76N range among subjects). Considering that the subjects had no instructions about what force levels to employ, the hold force was remarkably stable during individual trials and highly similar among trials. Even during the split task, subjects opted to “hold” the morsel momentarily on ca. 50% of the trials with a similar, low contact force. For both tasks, subjects split the morsel by exerting a distinct, rapidly executed ramp increase in force. The split occurred at 7.8–10.3 N (range among subjects) bite force for the biscuit and 16.0–19.0 N for the peanut. The magnitude of the forces used during the hold phase were within the range over which most periodontal afferents are optimally sensitive to changes in force, i.e., forces below about 1 N. This observation suggested that the subjects automatically adjusted the force to maximize the availability of information from periodontal afferents and avoided higher forces at which the sensitivity of most afferents was not optimal. We further confirmed that the periodontal receptors serve a role in controlling the hold force by anesthetizing the periodontal tissues: subjects employed considerably higher and more variable hold forces, but there was no effect on the split phase. In addition, the morsel frequently escaped from the incisal edges of the teeth while the subject attempted to maintain it in position. It was concluded that subjects rely on signals from periodontal afferents to regulate the jaw muscles, particularly when they first contact, manipulate, and hold food substances between the teeth.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 46
    ISSN: 1432-1106
    Keywords: Magnetoencephalography (MEG) ; Motor cortex ; Somatosensory cortex ; Human ; Neuromagnetic source localisation ; Somatosensory evoked fields (SEFs) ; Movement-related magnetic fields (MRFs) ; Gating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated under three different experimental conditions: (1) electrical stimulation of the right index finger (task S); (2) voluntary movement of the same finger (M); (3) M+S condition, consisting of voluntary movements of the right index finger triggering the electrical stimulus at the very beginning of the electromyogram. The three conditions were administered in random order every 5–8 s. In addition, the task somatosensory evoked fields (task SEFs) gathered during condition (1) were compared with control SEFs recorded at the beginning of the experiment during rest. In all subjects the overlay of somatosensory stimulation on movement provoked a decrement in brain responsiveness (gating) as determined by the amplitude of gated SEFs. The latter was found as the difference between the neuromagnetic fields during M+S condition (overlaying of movement and sensory stimulation) minus neuromagnetic fields under M condition (M only). The gating effect was found to begin approximately 30 ms after movement onset, and to last for the whole period of the ongoing movement. The theoretical locus of gating was estimated by dipole localisation of the difference between task SEFs and gated SEFS using a moving dipole model. The site of the “early” gating effect (〈40 ms) was found to be more anteriorly located than the “later” (〉40 ms) gating effect. The task SEFs were found to be larger (significant after 30 ms) than the control SEFs elicited under the basal condition. The results are discussed with respect to timing, mechanism (centrifugal and centripetal), locus and selectivity of gating. In addition, the results are discussed with regard to clinical application (measuring attentional deficits in patients with impairments of higher mental functions and measuring gating deficits in patients with disturbed sensorimotor integration).
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 47
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 437-446 
    ISSN: 1432-1106
    Keywords: Tracking ; Motor control ; Reflex ; Stretch reflexes ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract When studying muscle stretch reflexes with tonic stimuli or making a clinical assessment of muscle tone, it is imperative that the subject does not track the stretch stimulus either consciously or unconsciously. Such tracking contaminates reflex responses with voluntary ones and so invalidates any conclusions reached. Ideally, the stimuli used should be beyond the speed of a person's tracking ability. Both experiments on tonic stretch reflexes and clinical assessment of muscle tone of necessity involve the application of perturbations to the same limb from which a response is to be measured. These perturbations produce different peripheral feedback from the limb, including particularly cutaneous signals but also different Golgi tendon and muscle spindle afference than would occur for similar movements made voluntarily. This combination of peripheral signals resulting from perturbation of a limb is referred to here as perturbational feedback. There is evidence in the literature that subjects can generate voluntary responses to same-limb perturbations within latencies normally accepted for reflexes. Such fast responses might enable faster targets to be tracked voluntarily. In this study the tracking frequency response for the forearm was investigated using sinusoidal and irregular target signals. Perturbations were applied to a manipulandum and the subjects were required to voluntarily track these perturbations under two conditions: (1) where their arm was secured in the manipulandum and therefore they had perturbational feedback of tracking errors and (2) where their tracking arm was not in contact with the manipulandum and they had only visual or kinesthetic feedback of tracking errors. For sinusoidal target inputs, perturbational feedback allowed superior tracking performance. Many subjects could produce good tracking responses at 5 Hz and some as high as 7 Hz. This is a considerably higher frequency than was found when perturbational feedback was not present and greater than has been reported in the literature for all other types of tracking (typically about 2 Hz). In contrast, when irregular signals having power up to 4 Hz were used, perturbational feedback conferred only a marginal advantage on tracking performance. The enhancement of sinusoidal tracking performance by feedback may be due to the fact that cyclic movements can be internally generated by the subject and minimal reference to external cues provided by perturbational feedback can be used to synchronise such self-generated movements with a target. In contrast, this proposed mechanism cannot be used for tracking of irregular targets. Since perturbational feedback did not improve the maximum tracking frequency for irregular targets, there was no evidence for the operation of a shorter latency, same-limb displacement response.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 48
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 477-482 
    ISSN: 1432-1106
    Keywords: Saccadic adaptation ; Short-term adaptation ; Transfer to head movements ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract During a sequence of eye saccades toward a target that is systematically displaced during initiation of the saccade, the oculomotor system adjusts saccadic amplitude and direction in less than 100 trials to directly reach the second target position. The goal of the present work was to test whether and under which conditions these short-term, adaptive modifications in eye movements are transferred from horizontal eye saccades to horizontal head-pointing movements. In the first series of experiments subjects had to execute head yaw rotations to an extent defined by verbal command (assessed movements). These head movements were not part of visually elicited gaze shifts. They were recorded before and after a period of saccadic adaptation. Saccades were adapted to reduced amplitudes by using target displacements from 30 to 20° and from 40 to 30°. After 40–50 trials per target displacement, the amount of eye saccade adaptation was 79% (30–20°) and 97% (40–30°) of the displacement amplitude. In the second series of experiments, visually triggered head movements to briefly illuminated targets (100 ms) were measured before and after adaptation. The data obtained from both series did not reveal a functionally significant transfer of saccadic adaptation to head movements. The amount of possible transfer given as a percentage of the amount of achieved adaptation was: assessed head movements, 40°, 1.9%, 20°, -8.6%; visually triggered movements, 40°, 5.1%, 20°, 10.0%. No values significantly deviated from zero.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 49
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 112 (1996), S. 103-111 
    ISSN: 1432-1106
    Keywords: Motor control ; Positron emission tomography ; Cerebral blood flow ; Grasp ; Imagined movements ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Positron emission tomography imaging of cerebral blood flow was used to localize brain areas involved in the representation of hand grasping movements. Seven normal subjects were scanned under three conditions. In the first, they observed precision grasping of common objects performed by the examiner. In the second, they imagined themselves grasping the objects without actually moving the hand. These two tasks were compared with a control task of object viewing. Grasp observation activated the left rostral superior temporal sulcus, left inferior frontal cortex (area 45), left rostral inferior parietal cortex (area 40), the rostral part of left supplementary motor area (SMA-proper), and the right dorsal premotor cortex. Imagined grasping activated the left inferior frontal (area 44) and middle frontal cortex, left caudal inferior parietal cortex (area 40), a more extensive response in left rostral SMA-proper, and left dorsal premotor cortex. The two conditions activated different areas of the right posterior cerebellar cortex. We propose that the areas active during grasping observation may form a circuit for recognition of hand-object interactions, whereas the areas active during imagined grasping may be a putative human homologue of a circuit for hand grasping movements recently defined in nonhuman primates. The location of responses in SMA-proper confirms the rostrocaudal segregation of this area for imagined and real movement. A similar segregation is also present in the cerebellum, with imagined and observed grasping movements activating different parts of the posterior lobe and real movements activating the anterior lobe.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 50
    ISSN: 1432-1106
    Keywords: GluR1 ; GABA ; Electron microscopy ; Cerebral neocortex ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Specimens of human cerebral neocortex were obtained during neurosurgical operations and studied by immunocytochemistry and electron microscopy, using antibodies to the glutamate receptor subunit GluR1 and gamma-aminobutyric acid (GABA). Many GluR1-positive pyramidal neurons and fewer GluR1-positive nonpyramidal neurons were present in the cortex. Non-pyramidal neurons were more heavily labelled for GluR1 than pyramidal neurons. Most GABAergic neurons were labelled for GluR1. The white matter was unstained, except for occasional labelled neurons. This pattern of GluR1 immunostaining is similar to that in rat cerebral cortex, but is different from that in the hippocampus and amygdala, where large numbers of pyramidal or projection neurons, but few non-pyramidal or GABAergic neurons, were labelled for GluR1.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 51
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 107 (1996), S. 479-485 
    ISSN: 1432-1106
    Keywords: Transcranial magnetic stimulation ; Learning and memory ; Cortical physiology ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We studied the role of the dorsolateral prefrontal cortex in procedural learning. Normal subjects completed several blocks of a serial reaction time task using only one hand without or with concurrent non-invasive repetitive transcranial magnetic stimulation. To disrupt their function transiently, stimulation was applied at low intensity over the supplementary motor area or over the dorsolateral prefrontal cortex contralateral or ipsilateral to the hand used for the test. Stimulation to the contralateral dorsolateral prefrontal cortex markedly impaired procedural implicit learning, as documented by the lack of significant change in response times during the task. Stimulation over the other areas did not interfere with learning. These results support the notion of a critical role of contralateral dorsolateral prefrontal structures in learning of motor sequences.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 52
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 108 (1996), S. 140-146 
    ISSN: 1432-1106
    Keywords: Perception ; Visuo-motor transformation ; Distance reproduction ; Pointing ; Internal representation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Two experiments were carried out: the control experiment and the doubling-distance experiment. In the control experiment subjects were presented with two visual stimuli whose distance was randomly varied. Subjects were required to reproduce the interstimulus remembered distance in two conditions. In one condition (reproduction by pointing) they pointed to a virtual position in space. In the other condition (visual reproduction) they matched the distance by using two other visual stimuli. In the doubling-distance experiment, distances between the two randomly presented stimuli were half of the distances used in the control experiment. Subjects were required to reproduce the double of the presented distance. As in the control experiment, reproduction was executed in two conditions: reproduction by pointing and visual reproduction. In both experiments variable and constant errors were measured. Pointing kinematics were also analysed. The results of the control experiment showed that subjects underestimated distance in reproduction by pointing, whereas they overestimated distance in visual reproduction. Variable errors increased with increasing distance, whereas they were not influenced by the type of reproduction. In the doubling-distance experiment, subjects generally overestimated distance by the same amount in both conditions. However, overestimation decreased with distance during reproduction by pointing. Pointing kinematics varied between the two experiments. The results of the control experiment confirm the hypothesis that perceptual judgement and visuo-motor transformation are two separate processes during which the same object attributes are independently analysed. However, the results of the doubling-distance experiment suggest that perceptual judgement and visuo-motor transformation use the same mechanisms when object attributes are deduced by mental elaboration.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 53
    ISSN: 1432-1106
    Keywords: Motor control ; Long loop reflexes ; Transcranial electrical stimulation ; Transcranial magnetic stimulation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Long-latency electromyographic (EMG) responses can be evoked in the first dorsal interosseous muscle (FDI) by unexpected slips of an object (skin stretch) held between the index and thumb, or by forcible adduction of the metacarpophalangeal joint (muscle stretch). The former type of response is due to stimulation of tactile afferents in the skin of the digits, whereas the latter also activates muscle receptors. Previous studies have provided good evidence that long-latency reflex responses to stretch of distal muscles involve activity in a transcortical reflex pathway. The present experiments examined whether cutaneous reflexes also utilise a transcortical route. Transcranial magnetic or electrical stimuli were given over the motor cortex to evoke EMG activity during the period of the long-latency reflex response. When evoked by muscle stretch the responses to magnetic stimulation were facilitated more than those to electric stimulation. In contrast, facilitation was equal during the long-latency reflex elicited by cutaneous stimulation. Because of the different ways in which electrical and magnetic stimuli are believed to activate the motor cortex, we interpret these results to mean that the long-latency response to skin stretch is not mediated by a transcortical mechanism in the majority of subjects, whereas that following muscle stretch is. However, these are average data. In a few individual subjects, the opposite results were obtained. We suggest that there may be differences between subjects in the transcortical contribution to long-latency reflex responses. The implication is that, under normal circumstances, several pathways may contribute to these responses. If so, the relative roles of the pathways may change during different tasks, and in pathological states lesions in one system may well be accompanied by compensatory changes in other systems.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 54
    ISSN: 1432-1106
    Keywords: Cutaneous afferents ; Precision grip ; Hand ; Sensorimotor integration ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Unexpected pulling and pushing loads exerted by an object held with a precision grip evoke automatic and graded increases in the grip force (normal to the grip surfaces) that prevent escape of the object; unloading elicits a decrease in grip force. Anesthesia of the digital nerves has shown that these grip reactions depend on sensory signals from the digits. In the present study we assessed the capacity of tactile afferents from the digits to trigger and scale the evoked grip responses. Using tungsten microelectrodes inserted percutaneously into the median nerve of awake human subjects, unitary recordings were made from ten FA I and 13 FA II rapidly adapting afferents, and 12 SA I and 18 SA II slowly adapting afferents. While the subject held a manipulandum between a finger and the thumb, tangential load forces were applied to the receptor-bearing digit (index, middle, or ring finger or thumb) as trapezoidal load-force profiles with a plateau amplitude of 0.5 – 2.0 N and rates of loading and unloading at 2 – 8 N/s, or as “step-loads” of 0.5 N delivered at 32 N/s. Such load trials were delivered in both the distal (pulling) and proximal (pushing) direction. FA I afferents responded consistently to the load forces, being recruited during the loading and unloading phases. During the loading ramp the ensemble discharge of the FA I afferents reflected the first time-derivative of the load force (i.e., the load-force rate). These afferents were relatively insensitive to the subject's grip force responses. However, high static finger forces appeared to suppress excitation of these afferents during the unloading phase. The FA II afferents were largely insensitive to the load trials: only with the step-loads did some afferents respond. Both classes of SA afferents were sensitive to load force and grip force, and discharge rates were graded by the rate of loading. The firing of the SA I afferents appeared to be relatively more influenced by the subject's grip-force response than the discharge of the SA II afferents, which were more influenced by the load-force stimulus. The direction in which the tangential load force was applied to the skin influenced the firing of most afferents and in particular the SA II afferents. Individual afferents within each class (except for the FA IIs) responded to the loading ramp before the onset of the subject's grip response and may thus be responsible for initiating the automatic increase in grip force. However, nearly half of the FA I afferents recruited by the load trials responded to the loading phase early enough to trigger the subject's gripforce response, whereas only ca. one-fifth of the SA Is and SA IIs did so. These observations, together with the high density of FA I receptors in the digits, might place the FA I afferents in a unique position to convey the information required to initiate and scale the reactive gripforce responses to the imposed load forces.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 55
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 108 (1996), S. 315-320 
    ISSN: 1432-1106
    Keywords: Posture control ; Precue ; Synergy ; Perturbation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract An experiment was conducted to determine the influence of auditory precuing on posture control. Specifically, the influence of a warning signal on the onset latencies of the gastrocnemius (G) and tibialis anterior (TA) muscles was determined. An audible 50-ms tone was presented to subjects standing on a moveable platform and preceded a perturbation to standing balance by 500 ms. The perturbations were produced by an anterior or posterior translation (3 cm at 30 cm/s) of the support surface. Unilateral electromyographic activity was recorded from G and TA muscles. In the first series of trials (series A), the muscle onset latencies following perturbations with a nondirectionally specific precue, an invalid precue, and no precue were compared. In the second series of trials (series B), muscle onset latencies following perturbations with a directionally specific precue, invalid precue, and no precue perturbations were compared. In series A, mean muscle onset latencies decreased following nondirectionally specific precues during forward and backward platform perturbations; respectively, TA 6% (91±9 ms to 86±9 ms) and G 7% (93±6 ms to 87±5 ms). During series B, the TA and G muscle onset latencies decreased following directionally specific precues by 10.4% (92±12 ms to 82±6ms) and 9.8% (92±9ms to 83±6ms), respectively. There were no significant differences between the types of precues. Thus, prior knowledge of a forthcoming balance perturbation reduces postural muscle onset latency times. In addition, specific prior knowledge reduces muscle onset latency time in the same manner as does nonspecific prior knowledge.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 56
    ISSN: 1432-1106
    Keywords: Nerve growth factors ; Neuronal plasticity ; Substantia nigra ; Tyrosine hydroxylase ; Image analysis ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Brain-derived neurotrophic factor (BDNF) has been shown to promote the survival of cultured fetal mesencephalic dopaminergic neurons of rat and human origin. In the present study, BDNF was tested for its ability to influence neuronal structure of dopaminergic neurons in dissociated cultures of human fetal ventral mesencephalon after 7 days in vitro. Following immunocytochemical staining for tyrosine hydroxylase, all surviving dopaminergic neurons were counted. Computer-assisted three-dimensional reconstructions of uniform randomly selected neurons cultured with 50 ng/ml BDNF (n=120) or without BDNF (n=80) were made. BDNF increased the number of surviving human dopaminergic neurons by 76%. Mean soma profile area was significantly enlarged by 18% in BDNF-treated neurons as compared to controls. Analysis of parameters of neuritic size and complexity in these cultures revealed that combined neuritic length, combined neuritic volume, and neuritic field area were increased by 60%, 125% and 129%, respectively, and the mean number of segments per cell was increased by 41%. A change in neurite complexity in BDNF-treated cultures was further confirmed by the Sholl's concentric sphere analysis. These results demonstrate that BDNF promotes development and differentiation of human fetal dopaminergic neurons in vitro.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 57
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 434-440 
    ISSN: 1432-1106
    Keywords: Head movements ; Visuomotor coordination ; Saccadic eye movement ; Latencies ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We compared the head movements accompanying gaze shifts while our subjects executed different manual operations, requiring gaze shifts of about 30°. The different tasks yielded different latencies between gaze shifts and hand movements, and different maximum velocities of the hand. These changes in eye-hand coordination had a clear effect on eye-head coordination: the latencies and maximum velocities of head and hand were correlated. The same correlation between movements of the head and hand was also found within a task. Therefore, the changes in eye-head coordination are not caused by changes in the strategy of the subjects. We conclude that head movements and saccades during gaze shifts are not based on the same command: head movements depend both on the actual saccade and on possible future gaze shifts.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 58
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 441-449 
    ISSN: 1432-1106
    Keywords: Presynaptic inhibition ; Ia fibres ; Spinal reflexes ; Gait ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Modulation of presynaptic inhibition of Ia afferents projecting monosynaptically to soleus motoneurones was investigated during human gait. Changes in presynaptic inhibition of Ia afferents were deduced from alterations in the amount of heteronymous soleus H-reflex facilitation evoked by a constant femoral nerve stimulation. It has been shown that this facilitation is mediated through a monosynaptic Ia pathway and that during its first 0.5 ms it is still uncontaminated by any polysynaptic effect and can be used to assess ongoing presynaptic inhibition of Ia terminals to soleus motoneurones. During gait, heteronymous facilitation was reduced with respect to its control value (rest during sitting) and modulated during the step cycle: it reached its maximum at mid-stance and decreased to near zero by the end of stance. At the same time the H-reflex amplitude was to some extent similarly modulated. It is argued that this decrease in heteronymous Ia facilitation and in H-reflex amplitude reflects an increased, ongoing presynaptic inhibition of Ia terminals projecting onto soleus motoneurones, which could be from central and/or peripheral origin. D1 inhibition, i.e. the late and long-lasting inhibition of the soleus H-reflex evoked by a train of stimuli to the common peroneal nerve, was used as another method to assess presynaptic inhibition. This D1 inhibition was decreased during gait, and it is argued that this decrease might reflect an occlusion in presynaptic pathways or increased presynaptic inhibition of pathways mediating the conditioning volley.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 59
    ISSN: 1432-1106
    Keywords: Propriospinal premotoneurone ; Transcranial stimulation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We tested the hypothesis that some of the electromyographic (EMG) responses elicited in preactivated forearm muscles by transcranial stimulation of the human motor cortex are produced by activity in a disynaptic corticospinal linkage involving propriospinal-like interneurones with cell bodies in the spinal C3–4 segments. The experimental design incorporated a previous observation that stimulation of afferents in the superficial radial nerve inhibits propriospinal-like neurones projecting to the extensor carpi radialis (ECR) muscle. Surface EMG responses were recorded from the active ECR muscle after transcranial electrical or magnetic stimulation over the motor cortex. In random trials, single conditioning stimuli at twice perceptual threshold were given to the superficial radial nerve at the wrist at different times before a cortical shock. When the cortex was stimulated electrically, the conditioning stimulus suppressed the EMG responses when the interval between the shocks was 11 ms or more. This was about 3.5 ms longer than the minimum time calculated for a possible direct cutaneous effect on spinal motoneurones. The time course of suppression began earlier and was more complex during magnetic stimulation of the cortex. It is argued that this difference is due to the repetitive I waves generated by the magnetic shock. Whether electrical or magnetic stimulation was used, the first 1–3 ms of the EMG response was relatively unaffected by superficial radial nerve stimulation at any interstimulus interval, whereas clear suppression was seen in the later portion of the response. In contrast, if the EMG response in ECR was suppressed by a conditioning stimulus to the median nerve at the elbow, then all portions of the EMG response were inhibited including the first 1–3 ms. The median nerve effect is thought to be due to direct reciprocal inhibition of the extensor motoneurones. Thus sparing of the initial part of the cortically evoked response with superficial radial stimulation suggests that the latter type of inhibition occurs at a premotoneuronal level. The timing of the effect is compatible with the explanation that corticospinal excitation is produced in ECR motoneurones through both monosynaptic and disynaptic (including propriospinal premotoneuronal) pathways, with superficial radial nerve inhibition being exerted at the propriospinal level.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 60
    ISSN: 1432-1106
    Keywords: Memory-guided saccades ; Visuo-guided saccades ; Extraocular proprioception ; Vibration ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It is nowadays generally recognized that saccades to remembered targets are planned in a craniotopic frame of reference by combining retinal input with eye position signal. The origin of the eye position signal is still a matter of controversy, however. Does it arise from an efferent copy or is it supplied by the sensory receptors with which the extraocular muscles are endowed? When applied to skeletal muscles, vibration elicits spindle responses simulating a stretching of the vibrated muscle. When vibration is applied to the inferior rectus muscle (IR), it induces the illusion that a stationary fixating point is moving upward. Here we attempted to change the initial eye position signal supplied to the oculomotor system before a memory- or visuo-guided saccade to a 10° left target by applying mechanical vibration to the IR muscle. We wanted to determine whether modifying extraocular proprioceptive cues during the programming phase of a saccade might affect the latter's trajectory. In the memory-guided condition, it was observed that the saccades ended lower down when vibration was applied than in the control condition. Conversely, the visuo-guided saccades were not affected by the vibration. The above results mean first that extraocular proprioceptive cues are used as an initial eye position signal when a memory guided saccade has to be planned. Secondly, they suggest that extraocular proprioception may not be used to produce a visuo-guided saccade, or that this type of saccade is computed solely on the basis of retinal cues.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 61
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 79-99 
    ISSN: 1432-1106
    Keywords: Visual evoked potentials ; Visual cortex ; Functional specialization ; Stationary patterns ; Depth cues ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This paper describes the first of two complementary studies designed to identify and to investigate the properties and likely functional significance of independently generated components of scalp-recorded responses evoked by stationary patterns. These experiments compared the influence of various stimulus parameters, including site of stimulation, pattern form, nature of background field and several binocular and monocular depth cues on a single subject's visual evoked potentials. The results revealed the presence, inter alia, of two topographically distinct components with the following properties. The earlier component (C2), whose polarity depends on the stimulus location in the visual field, is: contour-specific; best evoked by discrete pattern elements, but not gratings, in the central few degrees of the visual field; insensitive to any depth cues. By contrast, the later (consistently) negative potential (LNP) is not dependent on the form of the stimulus and is larger for paracentrally (beyond 1.5°) than centrally located stimuli. It is also selectively enhanced by both monocular and binocular depth-cue stimuli, including the simulated forward movement of a pattern relative to a steady textured background; a stimulus which evokes no C2. The respective response properties of these scalp potentials suggest that there is parallel processing of depth- and contour-related features of stationary stimuli in anatomically separate regions of the human visual cortex.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 62
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 131-138 
    ISSN: 1432-1106
    Keywords: Gap effect ; Parkinson's disease ; Saccadic eye movements ; Express saccades ; Reaction time ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Application of the “gap paradigm” reduces mean saccadic reaction time (SRT). It enhances oculomotor response, sometimes showing express-like reactions within about 100–140 ms from target onset, which are called “express saccades.” Despite some controversy, there is evidence that express and regular saccades may be controlled by different pathways, but it is still not clear which pathways are involved in the generation of express saccades. It was suggested that the substantia nigra (SN) could take part in the control of these saccades. We compared saccadic reaction times of 14 patients with mild to moderate Parkinson's disease (PD), which commonly affects the SN, with those of nine elderly normal subjects. The results show a clear gap effect and no significant difference between mean saccadic reaction times and reaction time distributions of the PD and the control group. In the gap condition, express saccades are present in several subjects of both groups. Therefore, it is concluded that the deficits in the SN pars compacta due to PD, which affect directly and indirectly the activity of the SN pars reticulata that projects to SC, do not dominantly influence the process of preparing and executing express and regular saccades in patients with mild to moderate PD.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 63
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 110 (1996), S. 446-454 
    ISSN: 1432-1106
    Keywords: Magnetoencephalography ; Auditory cortex ; Directional hearing ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Auditory motion can be simulated by presenting binaural sounds with time-varying interaural intensity differences. We studied the human cortical response to both the direction and the rate of illusory motion by recording the auditory evoked magnetic fields with a 122-channel whole-head neuromagnetometer. The illusion of motion from left to right, right to left, and towards and away from the subject was produced by varying a 6-dB intensity difference between the two ears in the middle of a 600-ms tone. Both the onset and the intensity transition within the stimulus elicited clear responses in auditory cortices of both hemispheres, with the strongest responses occurring about 100 ms after the stimulus and transition onsets. The transition responses were significantly earlier and larger for fast than slow shifts and larger in the hemisphere contralateral to the increase in stimulus intensity for azimuthal shifts. Transition response amplitude varied with the direction of the simulated motion, suggesting that these responses are mediated by directionally selective cells in auditory cortex.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 64
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 112 (1996), S. 112-118 
    ISSN: 1432-1106
    Keywords: Monosynaptic reflex ; H-reflex variability ; Fractal ; Supraspinal ; Spinal cord injury ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In our previous study, $${1 \mathord{\left/ {\vphantom {1 {f^\beta }}} \right. \kern-\nulldelimiterspace} {f^\beta }}$$ -type power spectrum with the spectral exponent β significantly greater than zero was found in the variability of soleus H-reflex amplitudes. This result indicated that the H-reflex variability was time-correlated owing to fractal characteristics. Furthermore, it was also suggested that the fractal characteristics were generated at the spinal level. The purpose of the present study was to investigate whether the fractal nature of the H-reflex variability was influenced by the loss of supraspinal input. Six healthy normal subjects and seven patients with spinal cord injury participated in this study. Soleus H-reflexes were evoked every l s from both legs simultaneously (stimulation intensity: motor threshold) and 1050 successive amplitudes of the H-reflex were recorded. The H-reflex sequence evoked from each leg was analyzed by “coarse graining spectral analysis” to calculate the spectral exponent β. The value of β was used to evaluate the level of time-correlation (fractal correlation). Cross-spectral analysis was used to evaluate the degree of synchronization between the H-reflex sequences evoked from both legs. The β values for normal subjects (0.84±0.33, left leg; 0.88±0.34, right leg) were significantly greater (P〈0.001) than those for patients (0.31±0.18, left leg; 0.32±0.14, right leg), suggesting that the H-reflex sequences for normal subjects were more time-correlated than for patients. In the frequency range less than 0.2 Hz, the coherence of both legs was high (0.41±0.14) for normal subjects as compared to 0.20±0.12 for patients (P〈0.005). In this frequency range, the phase was almost 0 rad for normal subjects, indicating that the H-reflex variabilities of both legs were synchronized. These results suggested that (1) the strong fractal correlation observed in the H-reflex sequences for normal subjects was associated with supraspinal input, and (2) such supraspinal input had equal influence on the reflex arcs of the soleus of both legs.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 65
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 112 (1996), S. 277-288 
    ISSN: 1432-1106
    Keywords: Parkinson's disease ; Attention ; Three-dimensional object ; Coordinate systems ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study assessed the ability of mildly affected Parkinson's disease (PD) subjects (n=16) to perform attentional cognitive tasks within a three-dimensional object. A hollow cube was displayed on a computer screen and the subject was required to respond as quickly as possible to the highlighting of one of the cube angles by pressing the spacebar of the keyboard. Prior to the appearance of this imperative stimulus, the same (“valid” trials) or an alternative (“invalid” trials) angle was highlighted. For the invalid trials this meant that the subject oriented attention to the cued angle but, on imperative stimulus appearance, was unexpectedly required to redirect attention to another angle, which could be on a different cube face to that which had been cued. For one experimental session the cube was stationary, that is, object-centred and viewer-centred coordinates of a cube angle corresponded. For another session, the cube rotated such that the viewer-centred coordinates of an angle changed between appearance of the cue and appearance of the stimulus, but the angle's object-centred coordinates remained constant. The finding of lower reaction times for the valid than for the invalid trials, even when the cube was rotating, indicated that PD subjects could operate attention using an object-centred coordinate system. However, PD subjects showed exaggerated reaction times when the stimulus appeared in a cube face that was opposite to, rather than the same as, that of the invalidly cued angle. It is suggested that this reflects a dysfunction in the grouping of the structural components of the whole object at an attentional level.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 66
    ISSN: 1432-1106
    Keywords: Post stimulus time histograms ; Biceps brachii ; Brachioradialis ; Oligosynaptic group I inhibition ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Neural projection from the brachioradialis to the biceps brachii motoneurones in human was studied using the method of post-stimulus time histogram. Electrical stimulation to the radial branch innervating the brachioradialis produced inhibition in 11 out of 21 biceps motor units. The central delays of the inhibition were 0.7–1.2 ms longer than those of the homonymous facilitation. The inhibition was evoked with the intensity below the motor threshold. Pure cutaneous stimulation provoked no effects on the motor-unit firing. These findings suggest that group I afferents from the brachioradials mediate an oligosynaptic inhibition of the biceps brachii motoneurones.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 67
    ISSN: 1432-1106
    Keywords: Motor control ; Hemispace ; Kinematics ; Handedness ; Interhemispheric transmission ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Aiming movements made to visual targets on the same side of the body as the reaching hand typically show advantages as compared to aiming movements made to targets on the opposite side of the body midline in the contralateral visual field. These advantages for ipsilateral reaches include shorter reaction time, higher peak velocity, shorter duration and greater endpoint accuracy. It is commonly hypothesized that such advantages are related to the efficiency of intrahemispheric processing, since, for example, a left-sided target would be initially processed in the visual cortex of the right hemisphere and that same hemisphere controls the motor output to the left hand. We tested this hypothesis by examining the kinematics of aiming movements made by 26 right-handed subjects to visual targets briefly presented in either the left or the right visual field. In one block of trials, the subjects aimed their finger directly towards the target; in the other block, subjects were required to aim their movement to the mirror symmetrical position on the opposite side of the fixation light from the target. For the three kinematic measures in which hemispatial differences were obtained (peak velocity, duration and percentage of movement time spent in deceleration), the advantages were related to the side to which the motor response was directed and not to the side where the target was presented. In addition, these effects tended to be larger in the right hand than in the left, particularly for the percentage of the movement time spent in deceleration. The results are interpreted in terms of models of biomechanical constraints on contralateral movements, which are independent of the hemispace of target presentation.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 68
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 112 (1996), S. 381-391 
    ISSN: 1432-1106
    Keywords: nscranial magnetic stimulation ; Silent period ; Corpus callosum ; Primary motor cortex ; Inhibitory interneurones ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The objective of this study was to investigate interhemispheric transcallosal connections between primary motor cortices noninvasively in awake human subjects. For this purpose, focal transcranial magnetic stimulation was performed on eight healthy, right-handed subjects and one patient with congenital collosal agenesis. Using two magnetic stimulators, we investigated the effect of a conditioning magnetic stimulus applied to the motor cortex of one hemisphere on the duration of the silent period (SP) evoked in the first dorsal interosseus (FDI) muscle by a magnetic test stimulus given over the opposite motor cortex. It is well established that SP reflects activation of inhibitory interneurons within primary motor cortex. In all normal subjects, a conditioning stimulus to one hemisphere produced a significant shortening of SP evoked by the test stimulus when the conditioningtest-interval was 10–20 ms. The effect was also observed when an electrical test stimulus was used. The conditioning coil had to be placed over the hand motor area to obtain the maximal effect. The threshold for eliciting this decrease of SP duration was higher than the threshold for eliciting an early excitatory muscle response in the contralateral FDI. Increasing the intensity of the conditioning stimulus led to linear reduction of SP duration. In the patient with callosal agenesis, no such decreasing effect on SP duration was observed. These results suggest that inhibitory interneurons within primary hand motor cortex receive transcallosal inhibitory input from the opposite motor cortex. We propose that modulation of motor cortical interneurons via transcallosal pathways may provide a gain control for the motor cortical output system and subserve interhemispheric coordination in complex, nonsymmetrical bimanual movements.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 69
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 110 (1996), S. 131-141 
    ISSN: 1432-1106
    Keywords: Grasp force ; Tactile sensibility ; Proprioception ; Motor control ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Sensory inputs from the digits are important in initiating and scaling automatic reactive grip responses that help prevent frictional slips when grasped objects are subjected to destabilizing load forces. In the present study we analyzed the contribution to grip-force control from mechanoreceptors located proximal to the digits when subjects held a small manipulandum between the tips of the thumb and index finger. Loads of various controlled amplitudes and rates were delivered tangential to the grip surfaces at unpredictable times. Grip forces (normal to the grip surfaces) and the position of the manipulandum were recorded. In addition, movements of hand and arm segments were assessed by recording the position of markers placed at critical points. Subjects performed test series during normal digital sensibility and during local anesthesia of the index finger and thumb. To grade the size of movements of tissues proximal to the digits caused by the loadings, three different conditions of arm and hand support were used; (1) in the hand-support condition the subjects used the three ulnar fingers to grasp a vertical dowel support and the forearm was supported in a vacuum cast; (2) in the forearm-support condition only the forearm was supported; finally, (3) in the no-support condition the arm was free. With normal digital sensibility the size of the movements proximal to the digits had small effects on the grip-force control. In contrast, the grip control was markedly influenced by the extent of such movements during digital anesthesia. The poorest control was observed in the hand-support condition, allowing essentially only digital movements. The grip responses were either absent or attenuated, with greatly prolonged onset latencies. In the forearm and no-support conditions, when marked wrist movements took place, both the frequency and the strength of grip-force responses were higher, and the grip response latencies were shorter. However, the performance never approached normal. It is concluded that sensory inputs from the digits are dominant in reactive grip control. However, nondigital sensory input may be used for some grip control during impaired digital sensibility. Furthermore, the quality of the control during impaired sensibility depends on the extent of movements evoked by the load in the distal, unanesthetized parts of the arm. The origin of these useful sensory signals is discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 70
    ISSN: 1432-1238
    Keywords: Key words Closed-loop controlled ventilation ; Human ; Initial settings ; Computer ; Mechanical ventilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To test a method that allows automatic set-up of the ventilator controls at the onset of ventilation. Design: Prospective randomized crossover study. Setting: ICUs in one adult and one children’s hospital in Switzerland. Patients: Thirty intubated stable, critically ill patients (20 adults and 10 children). Interventions: The patients were ventilated during two 20-min periods using a modified Hamilton AMADEUS ventilator. During the control period the ventilator settings were chosen immediately prior to the study. During the other period individual settings were automatically determined by the ventilator (AutoInit). Measurements and results: Pressure, flow, and instantaneous CO2 concentration were measured at the airway opening. From these measurements, series dead space (V DS), expiratory time constant M28.6n(RC), tidal volume (V T), total respiratory frequency (f tot), minute ventilation (MV), and maximal and mean airway pressure (P aw,max and P aw,mean) were calculated. Arterial blood gases were analyzed at the end of each period. P aw,max was significantly less with the AutoInit ventilator settings while f tot was significantly greater (P〈0.05). The other values were not statistically significant. Conclusions: The AutoInit ventilator settings, which were automatically derived, were acceptable for all patients for a period of 20 min and were not found to be inferior to the control ventilator settings. This makes the AutoInit method potentially useful as an automatic start-up procedure for mechanical ventilation.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 71
    ISSN: 1432-1912
    Keywords: Human ; 5-HT1Dβ receptor structure ; 5-HT1Dβ receptor structure ; Radioligand binding ; Ketanserin ; Methiothepin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The study of serotonin receptor function has been complicated by the extreme molecular diversity of serotonin receptor subtypes, the lack of selective agonists and antagonists for many of the subtypes, and divergence in the pharmacological properties of a single receptor subtype across different animal species. An example of this pharmacological diversity between species homologues is provided by the 5-HT1D receptor subfamily. To further advance the ability to characterize and pharmacologically compare functional responses mediated by native 5-HT1D receptors, we have cloned the 5-HT1Dα and 5-HT1Dβ receptor subtypes from the rabbit and evaluated their pharmacological profiles using radioligand binding assays. The deduced amino acid sequences of the rabbit 5-HT1Dα and 5-HT1Dβ receptor genes displayed 60% overall identity [75% transmembrane (TM) identity] to each other and 〉 90% overall identity (95% TM identity) to their corresponding human homologues. Two compounds were identified in binding assays which discriminated between the closely-related 5-HT1D receptors. Ketanserin exhibited high affinity (pKi = 7.66) and selectivity ( 〉 20-fold) for the 5-HT1Dα receptor while methiothepin displayed high affinity (pKi = 7.86) and selectivity (16-fold) for the 5-HT1Dβ receptor subtype. The rabbit and human recombinant 5-HT1D receptors showed significant intraspecies (rabbit 5-HT1Dα vs. 5HT1Dβ) and interspecies (i.e. rabbit vs. human 5-HT1Dβ) similarities in their ligand binding profiles. These data suggest that 5-HT1D-mediated responses in rabbit preparations may provide information relevant to the pharmacology of the 5-HT1D receptor subtypes in humans.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 72
    Electronic Resource
    Electronic Resource
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 354 (1996), S. 765-772 
    ISSN: 1432-1912
    Keywords: Albino rabbit ; Pigmented rabbit ; Human ; Iris dilator ; α-Adrenoceptor subtype ; Imidazolines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The relative potency of α-adrenoceptor agonists and the dissociation constants of competitive antagonists were studied to characterize the post junctional α-adrenoceptor of the human iris dilator muscle. The data obtained from human iris dilator tissue was compared to that from rabbit. The iris dilator muscle was mounted in an organ bath and tension changes were recorded. (−)-Norepinephrine, (−)-phenylephrine (PE), oxymetazoline and p-aminoclonidine caused contractile responses in albino rabbit, pigmented rabbit and human iris dilator muscle in a concentration-dependent manner. The imidazoline molecules were partial agonists. In rabbit iris dilator, desensitization occurred to repeated oxymetazoline application at an interval of 1 h but recovery to the agonist activity was complete in about 3 h. Exposure to cocaine (10 μmol/l), hydrocortisone (100 μmol/l) and U-0521, a catechol-O-methyltransferase inhibitor (100 pmol/l), significantly potentiated the response to norepinephrine by 92-, 32- and 7 fold in iris dilator tissue of albino rabbit, pigmented rabbit and human, respectively. After block of “uptake1” and “uptake2”, the EC50 values of norepinephrine in the albino rabbit, pigmented rabbit and human iris dilator did not differ and ranged from 99 to 195 nmol/l. Small but significant potentiation by uptake blockers was also observed in the responses to PE in the albino rabbit or pigmented rabbit iris dilator. The average maximum tension induced by 100 μmol/l PE was 96 ± 11 mg (n = 10), 197 ± 11 mg (n = 11), 45 ± 5 mg (n = 27) in albino rabbit, pigmented rabbit and human iris dilator, respectively. In human iris dilator, the responses to PE were competitively antagonized by prazosin, 5-methylurapidil and phentolamine with apparent pKB values of 7.3, 6.6 and 7.5, respectively. The pK B values of the prazosin-PE interaction in iris dilator of albino and pigmented rabbit were 8.6 and 6.4, respectively. These results suggest that the post-junctional α-adrenoceptors in iris dilator may be similar to that in pigmented rabbit iris. The α-adrenoceptor of the human or pigmented rabbit iris dilator may be characterized as α1L-adrenoceptor subtype. The α-adrenoceptor of albino rabbit iris dilator appears to be a high affinity subtype. Furthermore, albino rabbit may not be the best strain for the drug research which is relevant to human ocular therapeutics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 73
    Electronic Resource
    Electronic Resource
    Springer
    Psychopharmacology 127 (1996), S. 359-364 
    ISSN: 1432-2072
    Keywords: Key words Tolerance ; Alcohol ; Placebo ; Drinking history ; Learning ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This research tested the hypothesis that a compensatory response to cues for alcohol contributes to the greater behavioral tolerance displayed by more experienced social drinkers. Sixty male social drinkers, ranging from 19 to 24 years of age, participated in the study. Thirty subjects had been drinking for 20 months or less (mean = 11.0 months), and were classified as novice (N) drinkers. The remaining 30 subjects had been drinking for 24 months or more (mean = 40.8 months), and were classified as experienced (E) drinkers. All subjects practiced a pursuit rotor task that measured psychomotor skill. Equal numbers of E and N subjects were then assigned to one of three groups (n = 10). Two groups were led to expect alcohol and performed the task after receiving either 0.56 g/kg alcohol, or a placebo. The third group received no beverage. E subjects displayed more behavioral tolerance to alcohol than did N drinkers. In accord with the hypothesis, E drinkers displayed a drug-opposite improvement in performance under a placebo, whereas N drinkers showed no appreciable change in performance. These observations support the hypothesis that the acquisition of a compensatory response to cues predicting the administration of alcohol contributes to the greater behavioral tolerance of more experienced drinkers.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 74
    ISSN: 1432-2072
    Keywords: Benzodiazepine ; Lorazepam ; Human ; Visual perception ; Oculomotor balance ; Integration processes ; Symmetry perception
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous studies have shown a lorazepam effect on visual perception. We tested whether this impairment resulted from a peripheral effect induced by benzodiazepines. A first experiment showed that a single dose of lorazepam induces an oculomotor imbalance without impairing visual acuity or accommodation. In a second experiment, we tested whether the impairment induced by lorazepam on visual perception still occurred in monocular vision. Subjects matched incomplete forms controlled on the spacing and alignment of their local contour elements. A reference object was first displayed and followed by two laterally displayed objects, a target and a distractor. The distractor was the mirror-reversed version of the target. Performance was impaired in the lorazepam group when the reference was an incomplete form with a spacing of 10.8' or 22.2' of arc. These results were not correlated with sedation. They confirm that lorazepam has a central deleterious effect on visual perception. A posthoc analysis also suggested that lorazepam-treated subjects used asymmetry in the stimuli as a compensatory strategy. This result is discussed in relation to previous hypotheses about the physiological mechanisms that determine the effects of lorazepam on visual perception.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 75
    ISSN: 1432-2072
    Keywords: Balanced placebo design ; Expectancy ; d-Amphetamine ; Subjective effects ; Self-administration ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The study examined the effects of expectation on the subjective effects and oral self-administration of 15 mgd-amphetamine (AMP) and placebo in 40 volunteers who reported no prior use of stimulants other than caffeine. A balanced placebo design was used to create four groups: told Placebo/got Placebo (P/P), told Placebo/got Stimulant (P/S), told Stimulant/got Placebo (S/P), told Stimulant/got Stimulant (S/S). There were three sessions. On one session (INFO), participants received a capsule containing AMP or placebo and were given information about the contents of the capsule according to the balanced placebo design. On another session (NO INFO), participants received no information about the capsule's contents and were given placebo. On the final session, participants were allowed to choose either the INFO or NO INFO capsule. Participants came to the laboratory to ingest their capsules, and then returned to their normal environments where they completed subjective effects questionnaires every 2 h for 8 h. Expectancies influenced the subjective effects reported during the INFO session, regardless of whether subjects actually received AMP or placebo: subjects who expected a stimulant had higher ratings of “feel drug” and “like drug”. The pharmacological effects of AMP were also evident on the INFO sessions: AMP produced its prototypic subjective effects regardless of subjects' expectancies. Significant interactions between drug and expectancy were obtained on self-report measures of anxiety and arousal: anxiety was higher for groups who received substances that did not match their expectations (P/S and S/P) and arousal increased most in volunteers who expected placebo but received stimulant. Choice of drug was determined primarily by pharmacology: participants who received AMP on the INFO session usually chose that capsule, regardless of information about its identity (P/S: 8/10; S/S: 9/10). In contrast, participants who received placebo on the INFO session chose this capsule at chance levels, regardless of information about its identity (S/P: 3/10; P/P: 6/10). Thus, expectancy influenced some of the subjective effects of AMP and placebo, but the pharmacological effects of the AMP were instrumental in determining whether volunteers would self-administer the drug.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 76
    ISSN: 1432-2013
    Keywords: Key words Muscle ; Contraction ; Myosin heavy chain ; Exercise ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The contractile characteristics of three human muscle groups (triceps surae, quadriceps femoris and triceps brachii) of seven young male subjects were examined. The contractile properties were determined from electrically evoked isometric responses and compared with fibre type composition determined from needle biopsy samples. Fibre types were identified using myosin heavy chain (MHC) isoforms as molecular markers with gel electrophoresis (SDS-PAGE) and histochemical ATPase staining. Four contractile parameters (twitch time to peak torque, the maximal rate of torque development, frequency response and fatiguability) were found to be related to fibre type composition. From the biopsy samples, single muscle fibres were isolated and chemically skinned. Isometric tension (P o) unloaded shortening velocity (V o) and rate of tension rise (dP/dt) were determined. Each fibre was classified on the basis of its MHC isoform composition determined by SDS-PAGE. Fibres belonging to the same type showed identical contractile parameters regardless of the muscle of origin, except minor differences in P o of the fast fibres and dP/dt of slow fibres. The results are in favour of the conclusion that fibre type composition, determined using MHC isoforms as markers, is the major determinant of the diversity of contractile properties among human muscle groups.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 77
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 107 (1996), S. 497-503 
    ISSN: 1432-1106
    Keywords: Heat pain threshold ; Adapting skin temperature ; Temporal summation ; Rate of stimulus rise ; Mechanical pain threshold ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We compared the effect of skin temperature on the critical threshold temperature eliciting heat pain with the effect of skin temperature on the response latency to the first heat pain sensation in healthy human subjects. Also, we determined the effect of the duration of a heat stimulus ramp on pain threshold. Furthermore, we determined the effect of skin temperature on mechanically induced pain. We found that the latency to the first pain sensation induced by a radiant heat stimulus was significantly decreased with an increase in the skin temperature (25–35 °C). However, independent of the rate of the stimulus rise (3–10 °C/s) and independent of the stimulus location (hairy vs glabrous skin), the threshold temperature for eliciting the heat pain sensation, determined with a contact thermostimulator, was not changed by a change in the skin temperature in the same subjects. With a fast rate of stimulus rise, a higher pain threshold was obtained than with a slow rise of stimulus temperature. However, this difference was found only with subject-controlled ascending stimuli (method of limits) but not with experimenter-controlled, predetermined stimulus ramps (method of levels). The heat pain threshold was higher in the glabrous skin of the hand than in the hairy skin of the forearm. With increasing stimulus duration (2.5–10s), the threshold temperature eliciting the heat pain sensation was significantly decreased. The mechanically induced pain threshold was not influenced by the skin temperature. The results indicate that the critical temperature for eliciting heat pain is independent of the skin temperature in humans. However, a change in skin temperature is an important source of an artefactual change in heat pain sensitivity when the radiant heat method (latency or energy) is used as an index of pain sensitivity. With a method dependent on reaction time (the method of limits), the heat pain threshold was artefactually increased, with fast rates of stimulus rise due to the long delay of slowly conducting heat pain signals in reaching the brain. With an increase in the duration of the heat stimulus, the critical temperature for eliciting pain sensation was significantly decreased, which may be explained by central neuronal mechanisms (temporal summation).
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 78
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 107 (1996), S. 463-478 
    ISSN: 1432-1106
    Keywords: Handedness ; Dynamics ; Rhythmic movement ; Synergies ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The symmetrical dynamics of 1∶1 rhythmic bimanual coordination may be specified by an order parameter equation involving the relative phase between rhythmic components, and an interlimb coupling which determines the relative attractiveness of in-phase and anti-phase patterns. Symmetry breaking of these dynamics can occur via the difference in the natural frequencies, Δω, of the left and right rhythmic components, or by the intrinsic asymmetrical dynamics of the body. The latter is captured by additional terms that render the symmetrical coupling slightly anisotropic. A major prediction resulting from this step is that although Δω=0, as the frequency of coordination is increased, the asymmetrical coupling will increase and the symmetrical coupling will decrease. This results in a greater left-limb bias in left-handers and right-limb bias in right-handers. This “increased handedness” prediction was confirmed in an experiment in which 20 left-handed and 20 right-handed individuals performed 1∶ 1 coordination with hand-held rigid pendulums. Manipulations of left and right pendulum lengths controlled Δω, and the coupled frequency was determined by a metronome. Also confirmed was the prediction that the small shift in equilibria from in-phase and anti-phase due to the intrinsic asymmetry should be amplified in left-handers when Δω 〉 0 and in right-handers when Δω 〈 0. Further, the bias in left-handers was more consistent than the bias in right-handers, and a subgroup of right-handers was identified who performed similarly to left-handers. The coordination dynamics of functional asymmetry provides insights into the elementary synergy between the limbs, the dynamical mechanism that modulates it, and the nature of the asymmetry in left-handed and right-handed individuals.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 79
    ISSN: 1432-1106
    Keywords: Muscle afferents ; Joint afferents ; Precision grip ; Hand ; Sensorimotor integration ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Pulling or pushing forces applied to an object gripped between finger and thumb excite tactile afferents in the digits in a manner awarding these afferents probable roles in triggering the reactive increases in grip force and in scaling the changes in grip force to the changes in applied load-force. In the present study we assessed the possible contributions from slowly adapting afferents supplying muscles involved in the generation of grip forces and from digital joint afferents. Impulses were recorded from single afferents via tungsten microelectrodes inserted percutaneously into the median or ulnar nerves of awake human subjects. The subject held a manipulandum with a precision grip between the receptor-related digit (index finger, middle finger, ring finger or thumb) and an opposing digit (thumb or index finger). Ramp-and-hold load forces of various amplitudes (0.5–2.0 N) and ramp rates (2–32 N/s) were delivered tangential to the parallel grip surfaces in both the distal (pulling) and the proximal (pushing) directions. Afferents from the long flexors of the digits (n=19), regardless of their muscle-spindle or tendon-organ origin, did not respond to the load forces before the onset of the automatic grip response, even with the fastest ramp rates. Their peak discharge closely followed the peak rate of increase in grip force. During the hold phase of the load stimulus, the afferents sustained a tonic discharge. The discharge rates were significantly lower with proximally directed loads despite the mean grip-force being similar in the two directions. This disparity could be explained by the differing contributions of these muscles to the finger-tip forces necessary to restrain the manipulandum in the two directions. Most afferents from the short flexors of the digits (n=17), including the lumbricals, dorsal interossei, opponens pollicis, and flexor pollicis brevis, did not respond at all, even with the fastest ramps. Furthermore, the ensemble pattern from the joint afferents (n=6) revealed no significant encoding of changes in finger-tip forces before the onset of the increase in grip force. We conclude that mechanoreceptors in the flexors of the digits and in the interphalangeal joints cannot be awarded a significant role in triggering the automatic changes in grip force. Rather, their responses appeared to reflect the reactive forces generated by the muscles to restrain the object. Hence, it appears that tactile afferents of the skin in contact with the object are the only species of receptor in the hand capable of triggering and initially scaling an appropriate change in grip force in response to an imposed change in load force, but that muscle and joint afferents may provide information related to the reactive forces produced by the subject.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 80
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 312-332 
    ISSN: 1432-1106
    Keywords: Eye movements ; Express saccades ; Attention ; Amplitude transition functions ; Superior colliculus ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Subjects were required to make a saccade to a target appearing randomly 4° to the left or right of the current fixation position (1280 trials per experiment). Location cues were used to direct visual attention and start saccade preparation to one of the two locations before target onset. When the cue indicated the target location (valid trials), the generation of express saccades (visually guided saccades with latencies around 100 ms) was strongly facilitated. When the opposite location was cued (invalid trials), express saccades were abolished and replaced by a population of mainly fast-regular saccades (latencies around 150 ms). This was found with a peripheral cue independently of whether the fixation point was removed before target onset (gap condition; experiment 1) or remained on throughout the trial (overlap condition; experiment 2). The same pattern also was observed with a central cue that did not involve any visual stimulation at a peripheral location (experiment 3). In the case where the primary saccade was executed in response to the cue and the target appeared at the opposite location, continuous amplitude transition functions were observed: starting at about 60–70 ms from target onset onward, the amplitude of the cue-elicited saccades continuously decreased from 4° to values below 1°. The results are explained by a fixation-gating model, according to which the antagonism between fixation and saccade activity gives rise to multimodal distributions of saccade latencies. It is argued that allocation of visual attention and saccade preparation to one location entails a successive disengagement of the fixation system controlling saccade preparation within the hemifield to which the saccade is prepared and a partial engagement of the opposite fixation system.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 81
    ISSN: 1432-1106
    Keywords: Posture ; Movement ; Bimanual coordination ; Motor learning ; Learning transfer ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present experimental series was designed to test the possibility that an anticipatory postural adjustment learned during the performance of a bimanual load lifting task may be transferred between the upper extremities. Eight seated subjects were asked to maintain horizontally one forearm (postural arm) loaded with a 1kg load, which was fixed to the arm by means of an electromagnet. The unloading was triggered either by the experimenter pressing a switch (control) or by the subjects making a voluntary movement with their other arm (moving arm). In the latter case, the subject lifted a 1-kg load resting on a force platform with the moving hand, and the switching off was triggered when the force level reached a threshold of 0.5 kg. The maximum amplitude (MA) and the maximum velocity (MV) of the postural forearm elbow joint rotation occuring after the unloading were measured at each trial. The learning process was estimated by performing a regression analysis on each series of trials, using an exponential model, and from the intercept of the regression curve with the ordinate. 1. During the original learning session (three series of 20 trials), a decrease in MA and MV was found to occur both within the series and between the series during a session. 2. After the initial learning session, the sides of the postural and moving arm were interchanged to test whether any transfer had occurred. The first series of trials in the second session (transfer) and the last series of trials in the original learning session were compared and found to be significantly different in terms of the intercept (seven subjects in the case of MA, five subjects in the case of MV) and the slope (five subjects), indicating a lack of transfer. 3. The data recorded during the second transfer learning session indicated that learning occurred in all eight subjects in the case of MA and in six subjects in the case of MV. It was observed that the original learning session did not facilitate the second one. 4. The lack of transfer of the anticipatory postural adjustment observed in this task is discussed with reference to the data in the literature.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 82
    ISSN: 1432-1106
    Keywords: Brain mapping ; Activation ; Functional, MRI ; Visual system ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Magnetic resonance imaging sensitized to activity-related changes in cerebral blood oxygenation was performed to map responses to selective stimulation of the parvo- and magnocellular visual pathways in calcarine and adjacent ventral occipital cortex of human subjects. In a repetitive stimulation protocol isoluminant chromatic or isochromatic luminance modulation was alternated with steady light of the same mean chromaticity and luminance as a reference condition. While no significant effects were observed for diffuse luminance modulation, two consistent cortical foci responded to isoluminant chromatic stimulation. A strong response was obtained in calcarine cortex at both 2 and 10 Hz, and even for selective S-cone stimulation. A second weaker colorsensitive response was seen bilaterally in the collateral sulcus. Thus, the data not only confirm color-sensitive activation in the collateral sulcus elicited in previous studies by selective cognitive tasks, but additionally demonstrate color-sensitive activation in primary visual cortex. With stimuli defined according to electrophysiological response properties of early visual processing stages, this study complements phenomenological or cognitive approaches in functional mapping of the human visual system.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 83
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 110 (1996), S. 482-486 
    ISSN: 1432-1106
    Keywords: Visual perception ; Proprioception ; Efference copy ; Two visual systems ; Emmert's law ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Recent models of the visual system in primates suggest that the mechanisms underlying visual perception and visuomotor control are implemented in separate functional streams in the cerebral cortex. However, a little-studied perceptual illusion demonstrates that a motor-related signal representing arm position can contribute to the visual perception of size. The illusion consists of an illusory size change in an afterimage of the hand when the hand is moved towards or away from the subject. The motor signal necessary for the illusion could be specified by feedforward and/or feedback sources (i.e. efference copy and/or proprioception/kinesthesis). We investigated the nature of this signal by measuring the illusion's magnitude when subjects moved their own arm (active condition, feedforward and feedback information available), and when arm movement was under the control of the experimenter (passive condition, feedback information available). Active and passive movements produced equivalent illusory size changes in the afterimages. However, the illusion was not obtained when an afterimage of subject's hand was obtained prior to movement of the other hand from a very similar location in space. This evidence shows that proprioceptive/kinesthetic feedback was sufficient to drive the illusion and suggests that a specific three-dimensional registration of proprioceptive input and the initial afterimage is necessary for the illusion to occur.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 84
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 110 (1996), S. 487-492 
    ISSN: 1432-1106
    Keywords: EEG ; Voluntary movement ; Auditory ; Steady-state response ; Evoked response ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It has not been clear whether or not early information processing in the human auditory cortex is altered by voluntary movements. We report a movementrelated, complex event-related potential consisting of relatively long-lasting amplitude and phase perturbations induced in an ongoing auditory steady-state response (SSR) by brief self-paced finger movements. Our results suggest that processing in the auditory cortex during the first 50–100 ms after stimulus delivery is affected before, during, and after voluntary movements, beginning with a 1- to 2-ms delay in the SSR wave form starting 1–2 s before the movement.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 85
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 100-112 
    ISSN: 1432-1106
    Keywords: Visual evoked potentials ; Stationary patterns ; Response composition ; Inter-subject variability ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The preceding study of the influence of various stimulus parameters on a single subject's pattern-on-set visual evoked potentials (VEPs) identified several constituent potentials with distinctive stimulus-related (and topographic) response properties. This paper describes related experiments in which an appropriate selection of the stimuli used in the original study, and some additional images of faces and other figures, were used to analyse and compare the composition of the VEPs recorded from 49 subjects. The results showed: (1) that the previously discovered response components were again easily identified: the early negative and late negative potentials, for example, were distinguishable in most subjects, not only by their different latencies and surface distributions, but also by the former's preferential, or more often selective, evocation by patterns of discrete elements compared with gratings, and the latter's selective enhancement by patterns containing monocular depth cues; (2) that there was considerable inter-individual variation in the relative sizes (as well as changes in latencies) of the basic components; (3) all the components were not always discernible in each individual's VEPs, and none was recorded for all 49 subjects; and (4) that because of these component amplitude variations, which were the main cause of variable overall response wave-forms, there was no simple relationship between the VEP peaks and underlying components. Some important methodological implications of these findings are discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 86
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 139-143 
    ISSN: 1432-1106
    Keywords: Eye movements ; Saccadic reaction time ; Express saccades ; Presaccadic potentials ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract When a temporal gap is introduced between the offset of the central fixation point and the appearance of a new target, saccadic reaction time is reduced (gap effect) and a special population of extremely fast saccades occurs (express saccades). It has been hypothesized that the gap triggers a readiness signal, which is responsible for the reduced saccadic reaction times. Here we recorded event-related potentials during the gap to in vestigate the central processes associated with the gener ation of fast regular saccades and express saccades. Prior to the execution of fast regular saccades, subjects pro duced a slow negative shift, with a maximum at frontal and central channels that started 40 ms after fixation offset. This widespread negativity is similar to a readiness potential. Anticipatory saccades were preceded by an increased frontal and parietal negativity. Prior to express saccades, a frontal negativity was observed, which started 135 ms after the disappearance of the fixation point. It is assumed that the frontal negativity prior to express saccades corresponds to the fixation-disengagement dis charge described in the frontal eye field of monkeys. Therefore, we hypothesize that fast regular saccades are the result of an increased readiness signal, while express saccades are the result of specific preparatory processes.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 87
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 253-261 
    ISSN: 1432-1106
    Keywords: Spatial localisation ; Proprioception ; Slow movement ; Multisensory integration ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To enable us to study how humans combine simultaneously present visual and proprioceptive position information, we had subjects perform a matching task. Seated at a table, they placed their left hand under the table concealing it from their gaze. They then had to match the proprioceptively perceived position of the left hand using only proprioceptive, only visual or both proprioceptive and visual information. We analysed the variance of the indicated positions in the various conditions. We compared the results with the predictions of a model in which simultaneously present visual and proprioceptive position information about the same object is integrated in the most effective way. The results are in disagreement with the model: the variance of the condition with both visual and proprioceptive information is smaller than expected from the variances of the other conditions. This means that the available information was integrated in a highly effective way. Furthermore, the results suggest that additional information was used. This information might have been visual information about body parts other than the fingertip or it might have been visual information about the environment.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 88
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 111 (1996), S. 296-304 
    ISSN: 1432-1106
    Keywords: Spasticity ; Stretch reflex ; Spinal cord ; l-dopa ; Monoamines ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Antispastic effects of the noradrenaline and dopamine precursor l-3,4-dihydroxyphelanine (l-dopa) were investigated in 11 subjects in which exaggerated stretch reflexes developed after spinal cord injuries. The effects were evaluated from changes in the electromyographic (EMG) response of the quadriceps muscle during tendon jerks evoked by standardized taps over the patellar tendon, in clonus and in resistance to passive movements of the limb. After administration of l-dopa, EMG responses occurring 30–150 ms after the tendon tap decreased to about 50% of control, and clinical tests revealed a marked decrease in the resistance to muscle stretches and in the degree of clonus. The effects were maximal within about 1 h. The depressive actions of l-dopa are interpreted as being exerted primarily at the spinal level, since they were evoked in paraplegics and tetraplegics. The results support the previous hypothesis that group II muscle afferents contribute to the exaggerated stretch reflex in spastic patients because l-dopa depresses transmission from group II but not from group I muscle afferents. They also indicate the possibility of using l-dopa in the treatment of spastic patients.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 89
    ISSN: 1432-1106
    Keywords: Transcranial magnetic cortical stimulation ; H-reflex ; Motor task ; Sequential and imagined movements ; Supplementary motor area ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Motor potentials (MEPs) evoked by focal (figure-of-eight coil) transcranial magnetic stimulation of the left motor cortex were recorded from the right opponens pollicis (OP) and flexor digitorum superficialis (FDS) of 14 normal subjects during different motor tasks. Changes in motor cortical excitability under behavioural conditions presumably connected with premotor and supplementary motor area (SMA) activation were investigated by comparing the size of the MEPs obtained during: (1) rest, (2) mental calculus, (3) repetitive left thumb-to-index opposition, (4) mental simulation of the same task with the right hand, (5) sequences of left thumb-to-fingers opposition, and (6) mental simulation of the same sequences with the right hand. MEP size significantly increased in both muscles during sequential movements of the left hand and sequence simulation with the right hand, but not during mental calculus or actual or simulated repetitive movements. The H-reflex evoked in the OP and FDS muscles by electrical stimulation of the median nerve (at wrist and elbow, respectively) under the same experimental conditions did not show significant modifications. The increase in MEP size during non-routine actual or imagined sequences of finger movements supports the view that the SMA is activated under these conditions and that it exerts a direct facilitatory influence on the motor cortex.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 90
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 112 (1996), S. 127-134 
    ISSN: 1432-1106
    Keywords: Coordinate system ; Transformation ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of the present experiment was to determine the preferred visual “straight ahead” or anterior/posterior (a/p) axis at the perceptual level. The ability of 12 neurologically normal, young adult subjects to position a rod parallel to the head and trunk a/p axes while viewing eccentrically located visual targets were studied under six conditions: 1. fixed — subjects stood erect with the head aligned to the trunk and viewed a central target while visually aligning a hand-held rod to the head and trunk a/p axis. 2. eyes — subjects moved only their eyes to view eccentric targets and aligned the rod to the head and trunk a/p axis. 3. head-trunk — subjects viewed the eccentric targets by rotating the head about a vertical axis and aligned the rod to the trunk a/p axis. 4. head-head — subjects viewed the targets as in 3 and positioned the rod parallel to the head a/p axis. 5. trunk-head — subjects viewed the targets by rotating the trunk and head as a unit about the vertical axis and aligned the rod parallel to the head a/p axis (note that the head and trunk a/p axes were misaligned by the experimenter prior to target viewing). 6. trunk-trunk — subjects viewed targets as in 5 and positioned the rod parallel to the trunk a/p axis. Subjects performed 25–35 consecutive trials within each condition. Perceptual errors were similar for aligning the rod to the trunk and head a/p axes; however, moving the trunk produced much larger constant and variable perceptual errors than moving the head. In a second experiment, four subjects controlled the position of a lighted rod held by a robot arm in complete darkness. They were instructed to align the rod to either the head or trunk a/p axis under conditions similar to the fixed, head-trunk, and head-head tasks described above. Perceptual errors were much larger when aligning the rod to the head a/p axis than to trunk a/p axis when the head was moved. This shows that the trunk a/p axis is clearly preferred at the perceptual level when visual background cues are not present. These data strongly suggest that the visual coordinate system uses a trunk-fixed a/p axis to define the subjective straight-ahead direction and right/left position of a target. Implications of these findings for sensorimotor transformations in control of upper limb movements to visual targets are discussed.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 91
    ISSN: 1432-1106
    Keywords: Cervico-ocular reflex ; Adaptation ; Vestibular loss ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The horizontal cervico-ocular reflex (COR) was examined in five labyrinthine-defictive subjects (LDS), during both passive oscillations of the head on the trunk (HTexam) and of the trunk under the earthfixed head (THexam) at 0.1–0.5 Hz, peak angular displacement ±30°. Subjects were tested in the dark, before and immediately after adaptation to binocular magnifying (x1.9) and reducing (x0.6) lenses. During long-term adaptation, the LDS were exposed to the normal environment for 5 h while wearing lenses. Short-term adaptation experiments (15–20 min) consisted of sustained ocular following of a small LED in an otherwise dark room and in full-room illumination. This LED was either stationary in space whilst the subjects moved their head actively, or fixed on the chair and rotating with the trunk during head-fixed stimulation. In all five patients, magnifying lenses increased COR gain (peak slow-phase eye velocity/peak stimulus velocity), whereas reducing lenses reduced the gain. Under HTexam the gain changes were greater, more consistent and the phases approximately compensatory to head displacement, whereas during THexam the gain decreased and phase increased at higher frequencies. COR adaptation was observed during foveal stimulation alone, but the effects were stronger with added background illumination. Results during an imaginary target task showed that the gain can be influenced strongly by mental set. Our findings indicate a highly modifiable COR in subjects with loss of vestibular function. Both peripheral and foveal retinal information contribute to the plastic changes in COR gain. Somatosensory cues from the trunk as well as cognitive/perceptual factors may be involved in the modification of the COR, by providing information about the relevance of eye movements, and contribute to the stabilisation of gaze in space.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 92
    ISSN: 1432-1106
    Keywords: Sensory inputs ; Postural control ; Elderly adults ; Vision ; Proprioception ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The ability of young and elderly adults to keep a stable upright posture while facing changes in the availability of visual and/or propriomuscular information was investigated. The two sensory sources of information were alternatively available and withdrawn, jointly and separately, during 10-s alternating sequences. Vision was modified by means of liquid-crystal goggles, and proprioception was altered by means of tendon vibration of both antagonistic ankle muscles. Elderly adults were less stable than young adults when vision was withdrawn. Both groups were greatly affected when proprio-muscular inputs were altered by vibration. Under constant visual conditions and following a propriomuscular perturbation (i.e., vibration), elderly adults were unable to take advantage of the reinsertion of propriomuscular inputs. They showed a transient, decreased stability and were unable to fully recover during a 10-s period, whereas young adults were able to rapidly integrate the information to stabilize their posture. When both propriomuscular and visual inputs were withdrawn and concurrently reinserted, the elderly adults did not show a transitory increase in the velocity of the center of foot pressure. The present results extend findings on the inability of elderly adults to reconfigure rapidly the postural set following reinsertion of sensory inputs. The results also suggest that elderly adults have difficulties in taking advantage of sensory redundancy in postural control.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 93
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 108 (1996), S. 486-492 
    ISSN: 1432-1106
    Keywords: Prehension ; Reaching ; Movement planning ; Arm movement ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The kinematic changes associated with the manipulation and transport components during a prehensile movement were examined using an experimental paradigm that required alterations in only the manipulation component. Instead of starting with the thumb and index finger naturally together (control condition), subjects began the reach-to-grasp movement with their thumb and fingers fully extended (experimental condition). In contrast to the control condition, in the experimental conditions the thumb and index finger started to close during wrist transport, then opened again prior to object grasp. In addition, there was a brief inflection in the ascending portion of the velocity profile of the wrist in over half the trials. However, all the primary features of the transport component profile remained unaltered. The results suggest that there can be substantial reorganization of the grip aperture during the first part of the reach without altering the temporal and spatial relationships between grip aperture and transport as the object to be grasped is approached.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 94
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 108 (1996), S. 493-500 
    ISSN: 1432-1106
    Keywords: Prehension ; Motor control ; Altered hand position ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Past studies have examined the coupling of reach and grasp components during prehensile movements. Many of these studies have supported the view that these components reflect the output of two parallel, though temporally coupled, motor programs. When the grip aperture is Altered prior to the onset of prehension from its usual, normally flexed position to one of maximal finger extension, our previous work has shown that the grasp component appears to reorganize itself during the reach. This reorganization, consisting of a brief closing and reopening of the grip aperture, only slightly influenced the temporal components of the wrist transport. The present experiment continues this research theme by examining the characteristics of grip aperture reorganization through the comparison of the kinematics of prehension components during movements to two different size objects under normal and Altered grip aperture conditions. It was hypothesized that if the grip reorganization is task dependent it should be related to object size. The experiment found that in the Altered grip condition reorganization did occur, as indicated by a slight closing and reopening of the aperture without influencing the transport of the wrist. The amplitude of and the time to the observed inflection point in the aperture time course were related to object size. The velocity of grip closing for the large object showed double peaks, with the first substantially smaller than the second. Moreover, for the small object, the velocity of grip aperture closing also was double peaked, but the difference between peaks was less pronounced. These changes in grip velocity suggest that the grip reorganization is related to object size. No effect of Altered aperture was observed on the transport component. For both object sizes in the Altered condition, the final peak velocity of grip aperture was statistically significantly correlated with transport time and time to peak deceleration. In contrast, such correlations were not observed for the initial peak velocity of the grip aperture. Furthermore, time to maximum grip aperture was correlated with both time to peak wrist velocity and time peak to wrist deceleration. Thus, as the reach progressed toward the object, the grip and transport components became more interdependent. The results are consistent with the notion that, when a well-practiced, coordinated act such as prehension is confronted with an Altered grip posture at the onset of the reach, the grip can be reorganized during the transport to preserve the relative timing between them. Thus these data add to the growing awareness that not only is there temporal coupling between the reach and grasp components but that these components may be integrated by higher-order control mechanism.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 95
    ISSN: 1432-1106
    Keywords: Cognitive performance ; Positron emission tomography ; Supplementary motor area ; Parietal cortex ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Differences between two states of cerebral activation were studied in eight subjects by positron emission tomography (PET) of regional cerebral blood flow (rCBF) and subsequent statistical parameter mapping. Subjects had to respond to a row of numbers presented on tape. In one condition they had to repeat each number. In the other condition the last heard number had to be added to the number presented before. Cerebral activity specifically related to the serial addition task was distributed over supplementary motor area (SMA), left premotor cortex and superior dorsal parietal cortex bilaterally, without significant involvement of prefrontal cortex. This indicated circuitry related to mental performance characterised by a fixed strategy of executing serial manipulation of numbers within “internal space”. The main aim of this communication is to discuss the similarity between circuitry underlying higher order motor control and pure cognitive performance.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 96
    ISSN: 1432-1106
    Keywords: Magnetic stimulation ; Cortical stimulation ; Central sense of movement ; Kinaesthesia ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Previous reports suggest that magnetic cortical stimulation (MCS) of the motor cortex can elicit a sensation of movement (kinaesthesia) in paralysed limbs. To assess this sensory effect of MCS, we examined the accuracy of kinaesthetic perception of stimulus-induced right elbow flexion in six blindfolded, healthy subjects. Matching of movements elicited by MCS was compared with matching of passive elbow movements. Small flexion movements between 1.5 and 5° of angle were regularly overestimated by 50–100% when induced by MCS over the parietal cortex, whereas movements elicited by MCS over the frontal cortex or by passive elbow flexion were accurately estimated. Our results provide data compatible with the hypothesis of the existence of a “central sense of movement”. Activation of collateral branches projecting from the motor cortex to the sensory could be the underlying mechanism to this phenomenon.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 97
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 108 (1996), S. 463-472 
    ISSN: 1432-1106
    Keywords: Vestibulo-ocular reflex ; Velocity storage ; Head reorientation ; Semicircular canals ; Otolith organs ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The otolith-semicircular canal interaction during postrotatory nystagmus was studied in ten normal human subjects by applying fast, short-lasting, passive head and body tilts (15, 30, 45, or 90° in the roll or pitch plane) 2 s after sudden stop from a constant-velocity rotation (100°/s) about the earth-vertical axis in yaw. Eye movements were measured with three-dimensional magnetic search coils. Following the head tilt, activity in the semicircular canal primary afferents continues to reflect the postrotatory angular velocity vector in head-centered coordinates, whereas otolith primary afferents signal a different orientation of the head relative to gravity. Despite the change in head orientation relative to gravity, postrotatory eye velocity decayed closely along the axis of semicircular canal stimulation (horizontal in head coordinates) for large head tilts (90°) and also for small head tilts (15–45°) for reorientations in the pitch plane. Only for small head tilts (15–45°) in the roll plane was there a reorientation of the eye rotation axis toward the gravitational vector. This reorientation was approximately compensatory for 15° head tilts. For 30° and 45° head tilts the eye rotation axis tilted toward the gravitational vector by about the same amount as for 15° head tilts. These results suggest that, with the exception of small head tilts in the roll plane, there was no compelling data showing a relationship between the eye rotation axis and head tilt and that postrotatory nystagmus is largely organized in head-centered rather than gravity-centered coordinates in humans. This indicates a rudimentary, nonlinear, and direction-specific interaction of semicircular canal and otolith signals in the central vestibular system in humans.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 98
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 108 (1996), S. 473-485 
    ISSN: 1432-1106
    Keywords: Gaze direction ; Interaural intensity difference ; Sound localization ; Spatial coordinates ; Perception ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present study examines whether the direction of gaze can influence sound lateralization. For this purpose, dichotic stimuli with variable interaural level difference (ILD) were presented under different conditions of visual fixation. In experiment 1, subjects with their head fixed directed their gaze to a given target, simultaneously adjusting the ILD of continuous pure tone or noise stimuli so that their location was perceived in the median plane of the head. The auditory adjustments were significantly correlated with gaze direction. During eccentric fixation, the psychophysical adjustments to the median plane shifted slightly toward the direction of gaze. The magnitude of the shift was about 1–3 dB, over a range of fixation angles of 45° to either side. The eye position effect, measured as a function of pure-tone frequency, was most pronounced at 2 kHz and showed a tendency to decrease at lower and higher frequencies. The effect still occurred, although weaker, even when the eyes were directed to eccentric positions in darkness and without a fixation target. In experiment 2, the adjustment method was replaced by a two-alternative forced-choice method. Subjects judged whether sound bursts, presented with variable ILDs, were perceived on the left or right of the median plane during fixation of targets in various directions. Corresponding to experiment 1, the psychometric functions shifted significantly with gaze direction. However, the shift was only about half as large as that found in experiment 1. The shift of the subjective auditory median plane in the direction of eccentric gaze, observed in both experiments, indicates that dichotic sound is localized slightly to the opposite side, i.e., to the left when the gaze is directed to the right and vice versa. The effect may be related to auditory neurons which exhibit spatially selective receptive fields that shift with eye position.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 99
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 109 (1996), S. 92-100 
    ISSN: 1432-1106
    Keywords: Somatosensory cortices ; Deafferentation ; Spatial oriented movements ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Three patients with a severe somatosensory deficit consequent on damage of the right somatosensory cortices were required, while blindfolded, to point with their insensate thumb to select positions on the other left fingers. Given the absence of feedback, the motor performance of the insensate thumb appeared grossly impaired in all patients. However, all patients attained end-points with an accuracy greater than chance. This result suggests that spatial accuracy may not rely entirely on sensory feedback. A good accuracy of pointing was evinced also in potentially facilitating conditions where somatosensory and motor cues coming from the intact side during simultaneous movement of both thumbs, vision of stimulated point and final thumb position, and visuomotor imagery were available. Furthermore, in one patient, the accuracy of the insensate thumb in cued conditions was higher than in a reference baseline condition, thus indicating that motor and cognitive cues can help the motor performance of patients with cortical somatosensory lesions.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 100
    ISSN: 1432-1106
    Keywords: Motor cortex ; Exercise ; Transcranial magnetic stimulation ; Inhibition ; Paired stimuli ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Transcranial magnetic stimulation (TMS) causes the corticospinal system to become refractory to subsequent stimuli for up to 200 ms. We examined the phenomenon of paired pulse inhibition with TMS under conditions of rest, ongoing voluntary activation (isometric force generation), and at variable delays following activation (postactivation) of the wrist extensors of seven normal subjects. Paired stimuli were delivered to the motor cortex with a circular coil at 1.1 times motor evoked potential (MEP) threshold, with various interstimulus intervals. Voluntary activation caused a marked decrease in the variability of the ratio of the amplitude of the MEP evoked by the test pulse to that of the MEP evoked by the conditioning pulse. Marked inhibition of the MEP evoked by the test pulse was still present. Postactivation, however, caused a dramatic reversal of the inhibitory effect of the conditioning pulse in all subjects at interstimulus intervals ranging from 40 to 120 ms. This effect lasted for up to 10 s following the cessation of activation. MEPs to transcranial electrical stimulation were also inhibited by conditioning TMS, but postactivation did not reverse this inhibition, indicating that the reversal of paired pulse inhibition is intracortical. We conjecture that paired pulse inhibition reflects activity of inhibitory interneurons or inhibitory connections between cortical output cells that are inactivated in the postactivation state.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...