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Notes: Abstract Anal neosphincter formation with electrically stimulated gracilis muscle is used increasingly for the surgical treatment of fecal incontinence. An alternative to gracilis might be of interest if this muscle is not available. 30 semitendinosus muscles and 15 long heads of biceps femoris were investigated on human cadavers. In particular, the nerve and vascular supply of these muscles was studied, both representing basic factors for muscle transposition. The long head of biceps femoris m. was found to receive its dominant vascular supply from the first and second perforating artery and its nerve supply from one motor branch out of the sciatic nerve, both as described in literature. The examination of semitendinosus m., however, revealed new anatomical aspects in its vascular supply. In all cases semitendinosus m. was found to receive dominant vascular pedicles from the medial circumflex femoral artery close to the ischial tuberosity and the second perforating artery. The nerve supply consisted of two motor branches out of the sciatic nerve. Both muscles fulfilled several basic criterias for transposition to the anus. However, regarding these requirements, semitendinosus offered distinct advantages in comparison with the long head of biceps femoris. Due to its vascular and nerve topography, semitendinosus seems suitable to serve as an alternative to gracilis.

Notes: Abstract The one- or two-headed arrangement of the lateral pterygoid m. (LPM) was analysed by studying the motor nerve distribution within the muscular tissue. In all subjects, the main innervation of the lateral pterygoid m. came from the anterior trunk of the mandibular n. by one to three nerves. These nerves divided into five or six vertical branches which ramified into parallel horizontal tiny fibers. Consequently, the lateral pterygoid m. appeared to be divided into oblique sagittal planes and horizontal layers by the nerve branches, reflecting the multipennate organisation of the muscle. These layers can be selectively recruited during mandibular movements, ensuing a fine medial-lateral control. According to its nerve supply, the LPM has to be considered as a single unit made of independent functional musulo-aponeurotic layers even though its morphologic conformation is in one, two or three heads.

Notes: Summary The one- or two-headed arrangement of the lateral pterygoid m. (LPM) was analysed by studying the motor nerve distribution within the muscular tissue. In all subjects, the main innervation of the lateral pterygoid m. came from the anterior trunk of the mandibular n. by one to three nerves. These nerves divided into five or six vertical branches which ramified into parallel horizontal tiny fibers. Consequently, the lateral pterygoid m. appeared to be divided into oblique sagittal planes and horizontal layers by the nerve branches, reflecting the multipennate organisation of the muscle. These layers can be selectively recruited during mandibular movements, ensuing a fine medial-lateral control. According to its nerve supply, the LPM has to be considered as a single unit made of independent functional musulo-aponeurotic layers even though its morphologic conformation is in one, two or three heads.

Notes: Abstract  Dendritic cells (DC) are specialist antigen presenting cells which capture antigens in the periphery, migrate centrally, and present the processed antigens in the context of major histocompatibility complex and appropriate co-stimulatory molecules to T lymphocytes for the initiation of an immune response. DEC-205 has been identified as a putative antigen-uptake receptor, which is expressed abundantly on mouse DC. The recently cloned mouse DEC-205 cDNA predicts a molecular structure which has a marked similarity to the macrophage mannose receptor. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and cDNA library screening, we obtained the full coding region of human DEC-205 cDNA from the Hodgkin’s disease-derived L428 cell line. The predicted protein structure is a type I transmembrane protein of 1722 amino acids consisting of a signal peptide, cysteine-rich domain, fibronectin type II domain, ten carbohydrate recognition-like domains, transmembrane domain, and a cytoplasmic tail. Human DEC-205 is 77% identical to the mouse protein with completely conserved cysteines. The DEC-205 gene (LY75) was mapped to chromosome band 2q24 by somatic cell hybrid panel analysis and fluorescent in situ hybridization. Northern blot analysis detected 7.8 and 9.5 kilobase DEC-205 transcripts in myeloid, B lymphoid, and Hodgkin’s disease-derived cell lines. RT-PCR analysis indicated that immature blood DC contain a barely detectable amount of DEC-205 transcripts but these were markedly increased upon differentiation/activation.

Notes: Abstract  We describe a hitherto unknown functional IGKV gene, VkLa, belonging to the IGKV1 subgroup with exon 2 having only 94% similarity to the closest known IGKV gene, 1–13/1D-13 (L4/L18a). Genomic DNA sequences spanning from 5’ of the decanucleotide box to 3’ of the heptamer (649 bp) were cloned and sequenced from four individuals. The new gene encodes the conserved amino acids in the exons and contains no apparent defects in known regulatory intron sequences such as pd-box, dc-box, TATA-box, CCCT-elements, splice-sequences, initiation codon, and heptamer sequence. VkLa is therefore potentially functional and, correspondingly, we found transcripts of properly rearranged VkLa with somatical hypermutations. VkLa was found in 12 of 57 (21%) healthy Caucasians by a nested polymerase chain reaction and subsequent sequencing of exon 2. This finding shows that there is more inter-individual variation in the available IGKV gene repertoire than was hitherto assumed. Finally, we describe a minor correction in the IGKV1D-43 (L23) gene sequence.

Notes: Abstract  Some alleles of the major histocompatibility complex (MHC) genes have a reticulate pattern of evolution, probably resulting from the exchange of segments by gene conversion or recombination. Here we compare the extent and patterns of reticulate evolution among the classical class I and class II loci of the human MHC using the recently developed compatibility and partition matrix methods. A complex pattern is revealed with substantial differences among loci in the extent and pattern of reticulation. Extremely high levels of reticulation are observed at HLA-B and HLA-DPB1, high levels at HLA-A and HLA-DRB1, moderate levels at HLA-C and HLA-DQB1, and low levels at HLA-DQA1. The reticulate events are concentrated in the exons encoding the highly variable, peptide-binding domains, suggesting that the sequence combinations produced by these events are maintained by natural selection.

Notes: Abstract  The relative levels of guanine nucleotide-binding protein α-subunits Gi1α, Gi2α, Gi3α, Goα, Gsα, and Gx/zα were measured in neocortex removed at surgery from patients with intractable temporal lobe epilepsy. Immunoreactivity was quantified using specific polyclonal antisera against the Gα-subunits according to the Laurell “rocket” immunoelectrophoresis technique. We compared the G protein contents of spiking (active) and nonspiking (nonactive) cortical regions, based on intraoperative electrocorticography, within the same and different patients. There were no clear trends for lower or higher levels of G-protein subtypes to be found in the samples of protein extracts from nonspiking regions as compared to spiking regions. However, comparison of paired samples of spiking and nonspiking cortex within the same patient demonstrated that levels of certain G-protein subtypes were either increased or decreased in all patients. This indicates that cortical regions with enhanced neuronal activity may produce microzonal alterations in the levels of G proteins. Moreover, our results suggest that high levels of Gi1α and low levels of the other G-protein subtypes appear to be associated with a greater susceptibility to maintaining spiking activity.

Notes: Abstract  The relationship between phantom limb phenomena and cortical reorganization was examined in five subjects with congenital absence of an upper limb and nine traumatic amputees. Neuromagnetic source imaging revealed minimal reorganization of primary somatosensory cortex in the congenital amputees (M=0.69 cm, SD 0.24) and the traumatic amputees without phantom limb pain (M=0.27 cm, SD 0.25); the amputees with phantom limb pain showed massive cortical reorganization (M=2.22 cm, SD 0.78). Phantom limb pain and nonpainful phantom limb phenomena were absent in the congenital amputees. Whereas phantom limb pain was positively related to cortical reorganization (r=0.87), nonpainful phantom phenomena were not significantly correlated with cortical reorganization (r=0.34). Sensory discrimination was normal and mislocalization (referral of stimulation-induced sensation to a phantom limb) was absent in the congenital amputees. The role of peripheral and central factors in the understanding of phantom limb pain and phantom limb phenomena is discussed in view of these findings.

Notes: Abstract  In two experiments the involvement of relative and fixed coordinate systems in visuomotor transformations was examined. The experimental task required the successive performance of two movements in each trial, which had to “correspond” to different visual stimuli. One kind of visual display indicated target positions by way of different horizontal positions of a vertical line on a monitor (position mode), while the other indicated movement amplitudes by way of different lengths of a horizontal line (amplitude mode). Formal analysis of variances and covariances of successive individual movements led to the conclusion that in the position mode visuomotor transformations were based on a mixture of relative and fixed coordinate systems, while in the amplitude mode only a relative coordinate system was involved. Thus, visuomotor transformations can be characterized as mixtures of different coordinate systems, and their respective weights in the mixtures are task-dependent.

Notes: Abstract  It is currently controversial whether auditory events produce inhibition of return (IOR). Although some authors argue that this can arise, others propose that peripheral auditory cues do not produce the characteristic IOR pattern of delayed detection latencies for ipsilaterally presented auditory or visual targets, unless a saccade is made to the cued location. We suggest that these previous discrepancies may depend on whether attention is reoriented centrally following the peripheral sound. We presented spatially uninformative peripheral auditory cues prior to visual targets requiring speeded detection responses. IOR was found in the absence of eye movements, provided an auditory reorienting event was presented at central fixation between onset of the peripheral cue and the subsequent target, but not when the central reorienting event was visual. A subsequent experiment demonstrated that auditory IOR between successive targets is similarly significantly reduced in the absence of an appropriate central reorienting event. These results imply that auditory stimuli can induce IOR directly. Previous failures to demonstrate IOR following auditory cues may have been due to an opposing influence of long-lasting attentional facilitation at the cued location, rather than to the putative inability of auditory stimuli to engage oculomotor processes generating IOR.

Notes: Abstract  Normal human subjects were tested for their ability to discriminate the orientation of a square plaque tilted in depth, using two different tasks: a grasping task and a perceptual matching task. Both tasks were given under separate monocular and binocular conditions. Accuracy of performance was measured by use of an opto-electronic motion analysis system, which computed the hand orientation (specifically, a line joining the tips of the thumb and index finger) as the hand either approached the target during grasping or was used to match the target. In all cases there was a very strong statistical coupling between hand orientation and target orientation, irrespective of viewing conditions. However, the matching data differed from the grasping data in showing a consistent curvature in the hand-target relationship, whereby the rate of change of hand orientation as a function of object orientation was smaller for oblique orientations than for those near the horizontal or vertical. The results are interpreted as reflecting the operation of two different mechanisms for analysing orientation in depth: a visuomotor system (assumed to be located primarily in the dorsal cortical visual stream) and a perceptual system (assumed to be located in the ventral stream). It may be that the requirements of visuomotor control dictate a primary need for absolute orientation coding, whereas those of perception dictate a need for more categorical coding.

Notes: Abstract  The motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS) is inhibited when preceded by a subthreshold TMS stimulus at short intervals (1–6 ms; intracortical inhibition, ICI) and is facilitated when preceded by a subthreshold TMS at longer intervals (10–15 ms; intracortical facilitation, ICF). We studied changes in ICI and ICF associated with two motor tasks requiring a different selectivity in fine motor control of small hand muscles (abductor pollicis brevis muscle, APB, and fourth dorsal interosseous muscle, 4DIO). In experiment 1 (exp. 1), nine healthy subjects completed four sets (5 min duration each) of repetitive (1 Hz) thumb movements. In experiment 2 (exp. 2), the subjects produced the same number of thumb movements, but complete relaxation of 4DIO was demanded. Following free thumb movements (exp. 1), amplitudes of MEPs in response to both single and paired TMS showed a trend to increase with the number of exercise sets in both APB and 4DIO. By contrast, more focal, selective thumb movementsinvolving APB with relaxation of 4DIO (exp. 2) caused an increase in MEP amplitudes after single and paired pulses only in APB, while a marked decrease in MEPs after paired pulses, but not after single TMS, in the actively relaxed 4DIO. This effect was more prominent for the interstimulus interval (ISI) of 1–3 ms than for longer ISIs (8 ms, 10 ms, and 15 ms). F-wave amplitudes reflecting excitability of the alpha motoneuron pool were unaltered in APB and 4DIO, suggesting a supraspinal origin for the observed changes. We conclude that plastic changes of ICI and ICF within the hand representation vary according to the selective requirements of the motor program. Performance of more focal tasks may be associated with a decrease in ICI in muscles engaged in the training task, while at the same time ICI may be increased in an actively relaxed muscle, also required for a focal performance. Additionally, our data further supports the idea that ICI and ICF may be controlled independently.

Notes: Abstract  The effect of transcranial magnetic stimulation was investigated on presynaptic inhibition of Ia terminals in the human upper and lower limb. Presynaptic inhibition of Ia afferents was assessed by three different and independent methods: (1) heteronymous Ia facilitation of the H-reflex (assessing ongoing presynaptic inhibition of Ia afferents in the conditioning volley); (2) long-lasting inhibition of the H-reflex by a group I volley (D1 inhibition, assessing presynaptic inhibition on Ia afferents in the test volley); (3) measurement of the monosynaptic Ia peak evoked in single motor units by a homonymous or heteronymous volley (post stimulus time histogram method). The first two methods were used on the lower limb; the last two on the upper limb. Provided that the corticospinal volley and the explored Ia volley were directed to the same target motoneurones, cortical stimulation evoked significant and congruent changes: (1) In the lower limb, transcranial stimulation provided increased heteronymous Ia facilitation and decreased D1 inhibition, both of which suggest a decrease in presynaptic inhibition of Ia afferents; (2) in the upper limb, transcranial stimulation provided an increase in the radial-induced inhibition of the wrist flexor H-reflex and a decrease in the peak of monosynaptic Ia excitation in single units, both of which suggest an increase in presynaptic inhibition. Selectivity of corticospinal effects was explored by testing presynaptic inhibition of Ia afferents to soleus motoneurones and focusing the transcranial stimulation to excite preferentially different motor nuclei (soleus, quadriceps and tibialis anterior). A cortical-induced decrease in presynaptic inhibition of Ia afferents was seen when, and only when, cortical and peripheral Ia volleys were directed to the same motor nucleus.

Notes: Abstract  Kinematic abnormalities of fast multijoint movements in cerebellar ataxia include abnormally increased curvature of hand trajectories and an increased hand path and are thought to originate from an impairment in generating appropriate levels of muscle torques to support normal coordination between shoulder and elbow joints. Such a mechanism predicts that kinematic abnormalities are pronounced when fast movements are performed and large muscular torques are required. Experimental evidence that systematically explores the effects of increasing movement velocities on movement kinematics in cerebellar multijoint movements is limited and to some extent contradictory. We, therefore, investigated angular and hand kinematics of natural multijoint pointing movements in patients with cerebellar degenerative disorders and healthy controls. Subjects performed self-paced vertical pointing movements with their right arms at three different target velocities. Limb movements were recorded in three-dimensional space using a two-camera infrared tracking system. Differences between patients and healthy subjects were most prominent when the subjects performed fast movements. Peak hand acceleration and deceleration were similar to normals during slow and moderate velocity movements but were smaller for fast movements. While altering movement velocities had little or no effect on the length of the hand path and angular motion of elbow and shoulder joints in normal subjects, the patients exhibited overshooting motions (hypermetria) of the hand and at both joints as movement velocity increased. Hypermetria at one joint always accompanied hypermetria at the neighboring joint. Peak elbow angular deceleration was markedly delayed in patients compared with normals. Other temporal movement variables such as the relative timing of shoulder and elbow joint motion onsets were normal in patients. Kinematic abnormalities of multijoint arm movements in cerebellar ataxia include hypermetria at both the elbow and the shoulder joint and, as a consequence, irregular and enlarged paths of the hand, and they are marked with fast but not with slow movements. Our findings suggest that kinematic movement abnormalities that characterize cerebellar limb ataxia are related to an impairment in scaling movement variables such as joint acceleration and deceleration normally with movement speed. Most likely, increased hand paths and decomposition of movement during slow movements, as described earlier, result from compensatory mechanisms the patients may employ if maximum movement accuracy is required.

Notes: Abstract  The aim of this study was to demonstrate, if possible, vestibulospinal reflex responses in soleus using a stimulus known to be capable of exciting vestibular afferents, namely 100-dB (NHL) clicks. We were able to show short-latency electromyographic (EMG) responses after clicks in five of eight normal subjects, and then we compared these responses with those after transmastoid galvanic stimulation (12 normal subjects). Stimulation of the side towards which the head was rotated (i.e. the side facing backwards) with either clicks or the cathode (anode applied to the opposite side) gave an initial excitatory response in soleus, while click or cathodal stimulation of the opposite side (i.e. the side facing forwards) gave an initial inhibitory response. Onset latencies and modulation with changes in postural task were identical for both click- and galvanic-evoked responses. In addition, there was a significant correlation between the amplitudes of the responses in soleus after click and galvanic stimulation (R 2=0.72). These similarities suggest that the earliest reflex responses in soleus after clicks and galvanic stimulation may be mediated by a common central pathway. In contrast, there was no correlation between the amplitudes of responses evoked by 100-dB clicks in soleus and those evoked by the same stimulus in the sternocleidomastoid. We conclude that vestibular activation by clicks can evoke reflex responses in lower-limb muscles and these responses have similar characteristics to the earliest responses evoked by galvanic vestibular stimulation.

Notes: Abstract  This study analyses the anticipatory postural adjustments during the gait initiation process in children aged 2.5, 4, 6 and 8 years. In adults, anticipation during gait initiation includes a shift in the centre of foot pressure (CP) both backwards and towards the stepping foot. Backward displacement and the duration of the anticipation phase covary with the gait progression velocity reached by the subject at the end of the first step. In the present study, the children walked on a force plate that allowed us to calculate the acceleration of the centre of mass and the displacements of the CP. The results showed three main characteristics of the development of anticipatory behaviour: (1) The occurrence of anticipatory displacements of the CP increased progressively with age. Systematic backward anticipation was found for all children except one of the youngest, whereas the lateral displacement was systematically observed later, in the 6-year group; (2) the amplitude of the spatial parameters showed a significant increase with age; (3) contrary to the adult, the amplitude of the backward shift did not covary with the forthcoming velocity in the youngest groups. This covariation became significant at 6 years and remained significant at 8 years. The results showed that even if anticipatory behaviour was present in 2.5-year-old children it is only later that the child is able of more accurate tuning of feedforward control, probably due to better control of the overall postural adjustments.

Notes: Abstract  Anticipatory smooth pursuit before the expected appearance of a moving target can reduce the initial retinal blur caused by the 100-ms delay of visual feedback. Humans, though, can only voluntarily generate smooth velocities up to about 5°/s without a moving target. However, previous experiments have shown that repetitive brief presentations of a moving target every few seconds appear to charge an internal store, the contents of which can later be released to generate higher velocity anticipatory movements. This store’s longevity was assessed here by repetitively presenting a moving target for 500 ms at different known intervals up to 7.2 s. Target motion at 25°/s or 50°/s was tested, with presentations in alternate directions or the same direction. Anticipatory velocity, measured 100 ms after target onset, decreased with increasing interval for all target motion conditions. A decrease was still seen when accurate timing cues were given before each presentation, suggesting that the drive for anticipatory pursuit is held in a short-term store lasting a few seconds which can enhance the low velocities produced by volition alone. The results also demonstrate that high-velocity anticipatory pursuit helps to overcome the temporal delays in the system and allows target velocity to be matched at an earlier time.

Notes: Abstract  Somatosensory evoked potentials (SEPs) evoked by stimulation of the tibial nerve (TN) in the popliteal fossa, the sural nerve (Sur) at the lateral malleole, and an Achilles tendon (Achilles) tap were recorded before and during voluntary plantarflexion, dorsiflexion, and cocontraction of the ipsi- and contralateral foot in normal subjects. Suppression (gating) of the TN-SEP began around 60 ms before the onset of electromyographic activity (EMG), and became maximal 50–100 ms after the onset of EMG. Similar gating was observed for the SEP evoked by activation of muscle afferents (Achilles) and cutaneous afferents (Sur). The TN-SEP was similarly depressed at the onset of a plantarflexion as at the onset of dorsiflexion. A depression, although much smaller, was also observed at the onset of movement of the contralateral limb. The depression of the TN-SEP after the onset of EMG decreased when fast-conducting afferents were blocked by ischemia below the knee joint. The TN-SEP was equally depressed during tonic dorsiflexion, plantarflexion, and cocontraction of dorsi- and plantarflexors. The TN-SEP was depressed for up to 300 ms when preceded by stimulation of Sur or a biceps femoris tendon tap. Gating of lower limb SEPs thus appears to have both central and peripheral components of which neither seems to be specific for the muscle being contracted or the sensory afferents being stimulated. We encourage that caution is taken when drawing functional conclusions regarding movement-specific modulation of afferent inflow to the somatosensory cortex based on observations of gating of lower limb SEP.

Notes: Abstract  Orientation acuity was estimated for vertical and oblique bar stimuli. Discrimination thresholds were affected by changes in the length and width of the targets, falling as bar length was increased and, conversely, rising as the bars were made wider. These changes are complimentary, in that overall discrimination performance can be predicted by a single measure of the orientation “entropy” of the target, namely the height-to-width ratio. The data provide support for a model of orientation coding where discrimination performance is not simply a reflection of the signal-to-noise ratio in single cells in the striate cortex.

Notes: Abstract  Brain electrical source analysis (BESA) of the scalp electroencephalographic activity is well adapted to distinguish neighbouring cerebral generators precisely. Therefore, we performed dipolar source modelling in scalp medium nerve somatosensory evoked potentials (SEPs) recorded at 1.5-Hz stimulation rate, where all the early components should be identifiable. We built a four-dipole model, which was issued from the grand average, and applied it also to recordings from single individuals. Our model included a dipole at the base of the skull and three other perirolandic dipoles. The first of the latter dipoles was tangentially oriented and was active at the same latencies as the N20/P20 potential and, with opposite polarity, the P24/N24 response. The second perirolandic dipole showed an initial peak of activity slightly earlier than that of the N20/P20 dipolar source and, later, it was active at the same latency as the central P22 potential. Lastly, the third perirolandic dipole exaplaining the fronto-central N30 potential scalp distribution was constantly more posterior than the first one. In order to evaluate the effect of an increasing repetition frequency on the activity of SEP dipolar sources, we applied the model built from 1.5-Hz SEPs to traces recorded at 3-Hz and 10-Hz repetition rates. We found that the 10-Hz stimulus frequency reduced selectively the later of the two activity phases of the first perirolandic dipole. The decrement in strength of this dipolar source can be explained if we assume that: (a) the later activity of the first perirolandic dipole can represent the inhibitory phase of a “primary response”; (b) two different clusters of cells generate the opposite activities of the tangential perirolandic dipole. An additional finding in our model was that two different perirolandic dipoles contribute to the centro-parietal N20 potential generation.

Notes: Abstract  We assessed the suitability of using the Wing and Kristofferson model for timing repetitive motor responses to analyse timing variability during repetitive saccadic eye movements. The model decomposes total timing variability (TV) into a central timing component (CV) and a peripheral motor delay component (MV). Eight normal subjects made voluntary horizontal saccades, in darkness, in synchrony with a regular auditory metronome. After 20 saccades had been produced, the metronome was switched off and subjects continued responding at the same frequency until 31 further saccades had been made. Inter-saccade intervals (ISIs) from the unpaced phase were used to calculate TV, CV and MV. Three different target intervals, paced by auditory cues, were used – 496 ms, 752 ms and 1000 ms. In the paced phase, subjects’ ISIs closely matched the auditory cue intervals. In the unpaced phase, subjects were clearly able to respond at three different frequencies. As predicted by the Wing and Kristofferson model, the durations of successive ISIs tended to be negatively correlated. As expected, TV and CV increased with increasing ISI. Contrary to the expectation of the model that MV would remain constant, we found that it increased with increasing interval. Our results do not conclusively demonstrate the validity of applying the Wing and Kristofferson model to the analysis of timing variability during repetitive saccadic eye movements. However, comparison with previous studies shows that, at least in normal subjects, it is equally valid to apply the model to the analysis of repetitive saccadic eye movements as it is to apply it to the analysis of data from other effectors.

Notes: Abstract  Obstacle avoidance strategies are of two basic but interrelated types: moving around an obstacle to that body parts do not come too close, and slowing down. In reaching-to-grasp, avoidance may involve the transport component, the grasp formation component, or both. There has been little research that has directly examined obstacle avoidance strategies during reaches-to-grasp. Several recent reports describe experiments in which reaches-to-grasp were made when nontarget objects were present in the workspace. The effects of these nontargets were interpreted as being due to their distracting effects rather than their obstructing effects. The results of these studies are reinterpreted as being due to the non-target’s obstructing effects. The obstacle interpretation is more parsimonious and better predicts the pattern of results than the distractor interpretation. Predictions of the obstacle interpretation were examined in an experiment in which participants were required to reach to grasp a target in the presence of another object in various locations. The results were exactly in line with the interpretation of the object as an obstacle and the data show how grasp and transport movements are subtly adjusted so as to avoid potential obstacles. It is proposed that people move so as not to bring body parts within a minimum preferred distance from nontarget objects within the workspace. What constitutes the preferred distance in a particular context appears to depend upon the speed of movement and a variety of psychological factors related to the cost that a person attaches to a collision.

Notes: Abstract  Human arm movements towards visual targets are remarkably reproducible in several tasks and conditions. Various authors have reported that trajectories of unconstrained point-to-point movements are slightly curved, smooth and have bell-shaped velocity profiles. The hand paths of such movements show small - but significant – curvatures throughout the workspace. The cause of these curvatures is still obscure. Traditionally this curvature is explained as the result of an optimisation process or is ascribed to mechanical or dynamic properties of the effector system. Recently, however, it has been suggested that these curvatures are due at least partly, to the visual misperception of straight lines. To evaluate the latter hypothesis, we compared unconstrained, self-paced point-to-point movements that subjects made with their right and left hand. We assume that the visual misperception may depend on the position in the workspace, subject, etc. but not on the hand used to make the movement. Therefore we argue that if curvature is caused by a visual misperception of straight lines, curvatures should be the same for movements made with the left and right hand. Our experiments cast strong doubt on the hypothesis that curvatures are the result of a visual distortion, because curvatures of the left hand trajectories, mirrored in the mid-sagittal plane, are found to be accurately described by trajectories of the right hand. Estimates of the effect of visual distortion on movement curvature show that, if present, this effect is very small compared with other sources that contribute to movement curvature. We found that curvatures depend strongly on the subject and on the direction and distance of the movement. Curvatures do not seem to be caused purely by the dynamic properties of the arm, since curvatures do not change significantly with increasing movement velocity. Therefore, we conclude that curvatures reflect an inherent property of the control of multi-joint arm movements.

Notes: Abstract  The effect of horizontal head position on the lateralization of dichotic sound stimuli was investigated in four experiments. In experiment 1, subjects adjusted the interaural level difference (ILD) of a stimulus (band-pass noise) to the subjective auditory median plane (SAMP) while simultaneously directing the beam of a laser attached to the head to visual targets in various directions. The adjustments were significantly correlated with head position, shifting in a direction toward the side to which the head was turned. This result was replicated in experiment 2, which employed a two-alternative forced-choice method, in which stimuli of different ILD were presented and left/right judgments were made. In both experiments, the average magnitude of the shift of the SAMP was about 1 dB over the range of head positions from straight ahead to 60° to the side. The shift of the SAMP indicates that any shift in head position induces a change in sound lateralization in the opposite direction, i.e., the intracranial sound image is shifted slightly to the left when the head is directed to the right and to the right when the head is to the left. In experiments 3 and 4, the effect of head position was compared with that of eye position by using the same methods as in experiment 2. Both shifts in SAMP, induced by either head- or eye-position changes, are in the same direction and, on average, of about the same magnitude (experiment 3), and head- and eye-position effects compensate approximately for each other during variations of head position when the gaze remains fixed to a visual target in space (experiment 4).

Notes: Abstract  Muscle pain generally has an inhibitory effect on voluntary orofacial motor function. However, it is not known whether muscle pain causes direct or indirect changes in motoneuron excitability. In this study a monopolar needle stimulation technique was used to evoke the direct motor response (M-response) in the left masseter muscle and the heteronymous H-reflex in the left temporalis muscle as an indirect measure of motoneuron excitability. Series of 20 repeated electrical stimuli were delivered at 50% of maximal voluntary contraction (MVC) before, during, and after periods with experimental jaw-muscle pain in 11 healthy subjects. Pain was induced by standardized infusion of hypertonic (5%) saline into the mid-portion of the right masseter muscle. The mean pain intensity rating on a 100-mm visual analog scale was 42±5 mm. The short-latency responses (less than 6 ms) could be evoked in all subjects. Analysis of the latency and amplitude of the temporal H-reflex indicated no significant effect of jaw-muscle pain. The amplitude of the masseteric M-response was significantly smaller in the postpain condition than in the pain conditions (ANOVA, P=0.018), but no differences were found between the prepain and postpain conditions. In nine subjects, poststimulus periods (mean offset latency, 69.6±8.6 ms) with significantly (more than 50%) suppressed EMG activity were detected in the ipsilateral masseter muscle following the M-response (mean offset latency, 5.5±0.2 ms). These reflex responses did not show a systematic change during the pain conditions. In conclusion, acute contralateral jaw-muscle pain does not seem to modulate the motoneuron excitability as measured by the heteronymous H-reflex.

Notes: Abstract  We used anterograde and retrograde transsynaptic pathway tracing techniques to reveal the retinal origin and the cortical termination of the expanded retino-geniculo-middle suprasylvian (MS) cortex pathway in adult cats which sustained lesions of areas 17 and 18 on the day of birth (P1) or at 1 month of age (P28). Following anterograde transsynaptic transport of tritiated amino acids from the eye, four major results were obtained: (1) a strong and specific pathway from retina through dorsal lateral geniculate nucleus (dLGN) to the posterior half of MS cortex was identified; this pathway is a substantial expansion of an insignificant pathway present in intact cats; (2) the terminus of the pathway was lower layer III and layer IV; (3) contralateral projections were stronger than ipsilateral projections; (4) projections in P28 cats were stronger than those in P1 cats. Following retrograde transsynaptic transport of WGA-HRP from posterior MS cortex, four additional results were obtained: (1) the pathway was enlarged and visuotopically organized; (2) the pathway arose primarily from α- and γ-retinal ganglion cells; (3) a small number of β-cells in P1 cats and a modest number in P28 cats also contribute to the pathway; (4) the combined numbers of γ- and β-cells relative to α-cells was greater in temporal retina than in nasal retina. The combined demonstration of both origin and terminus of the pathway with transsynaptic tracers argued strongly for high levels of coupling between primary and secondary pathway limbs in both P1 and P28 cats. This level of coupling, as well as other features of the pathway, have much in common with the retino-geniculo-17/18 pathway of intact cats. However, the retino-geniculo-MS system in P1 cats transmits primarily Y and W signals, in P28 cats X, Y, and W signals; whereas the retino-geniculo-17/18 pathway transmits primarily X and Y signals. These results have implications for understanding the repercussions of early visual cortex lesions in monkeys and humans.

Notes: Abstract  The present study investigates the efficacy of visual stabilisation of posture for different spatial frequencies of a visual stimulus. Circular sine wave gratings were used to analyse the correlation between perception of motion in depth and stabilisation of fore-aft sway by the mechanism of detecting changes in target size. Body sway was recorded by a force-measuring platform (series A) and, in addition, by simultaneous tracking of infrared markers fixed to the subject’s body (series B). Mean velocity and amplitude (RMS) of body sway were calculated in both sagittal (a–p) and lateral (l–r) planes. Sagittal sway was of least magnitude when viewing contrast gratings with lowest thresholds, whereas higher thresholds resulted in increasing sway parameters. As intended by the design of the stimuli, sagittal sway was correlated closer with the stabilising effect exerted by the different stimuli than was lateral sway. Sway velocity was reduced more efficiently, however, with a lower correlation with the psychophysical transfer function, than was RMS sway. Since sway velocity measured by the platform is suggested to depend to a greter extent on dynamic muscle forces generated at each individual body site the results indicate that visual information can be used to reduce and thereby optimise dynamic muscle action (sway velocity) even though static body sway is either not or less reduced. A comparable economisation of sway velocity but not of RMS sway was also seen at the end of posture investigations, indicative of positive training effects.

Notes: Abstract  Interactions between proprioceptive and vestibular inputs contributing to the generation of balance corrections may vary across muscles depending on the availability of sensory information at centres initiating and modulating muscle synergies, and the efficacy with which the muscle action can prevent a fall. Information which is not available from one sensory system may be obtained by switching to another. Alternatively, interactions between sensory systems and the muscle to which this interaction is targeted may be fixed during neural development and not switchable. To investigate these different concepts, balance corrections with three different sets of proprioceptive trigger signals were examined under eyes-open and eyes-closed conditions in the muscles of normal subjects and compared with those of subjects with bilateral peripheral vestibular loss. The different sets of early proprioceptive inputs were obtained by employing three combinations of support surface rotation and translation, for which ankle inputs were nulled, normal or enhanced, the knees were either locked or in flexion, and the trunk was either in flexion or extension. Three types of proprioceptive and vestibulospinal interactions were identified in muscles responses. These interactions were typified by the responses of triceps surae, quadriceps, and paraspinal muscles. The amplitudes of stretch responses at 50 ms after the onset of ankle flexion in triceps surae muscles were related to the velocity of ankle stretch. The amplitude of balance-correcting responses at 100 ms corresponded more with stretch of the biarticular gastrocnemius when the knee was re-extended at 60 ms. Absent stretch reflexes at 50 ms in triceps surae with nulled ankle inputs caused a minor, 12-ms delay in the onset of balance-correcting responses in triceps surae muscles. Vestibular loss caused no change in the amplitude of balance-correcting responses, but a negligible decrease in onset latency in triceps surae even with nulled ankle inputs. Stretch responses in quadriceps at 80 ms increased with the velocity of knee flexion but were overall lower in amplitude in vestibular loss subjects. Balance-correcting responses in quadriceps had amplitudes which were related to the directions of initial trunk movements, were still present when knee inputs were negligible and were also altered after vestibular loss. Stretch and unloading responses in paraspinals at 80 ms were consistent with the direction of initial trunk flexion and extension. Subsequent balance-correcting responses in paraspinals were delayed 20 ms in onset and altered in amplitude by vestibular loss. The changes in the amplitudes of ankle (tibialis anterior), knee (quadriceps) and trunk (paraspinal) muscle responses with vestibular loss affected the amplitudes and timing of trunk angular velocities, requiring increased stabilizing tibialis anterior, paraspinal and trapezius responses post 240 ms as these subjects attempted to remain upright. The results suggest that trunk inputs provide an ideal candidate for triggering balance corrections as these would still be present when vestibular, ankle and knee inputs are absent. The disparity between the amplitudes of stretch reflex and automatic balance-correcting responses in triceps surae and the insignificant alteration in the timing of balance-correcting responses in these muscles with nulled ankle inputs indicates that ankle inputs do not trigger balance corrections. Furthermore, modulation of balance corrections normally performed by vestibular inputs in some but not all muscles is not achieved by switching to another sensory system on vestibular loss. We postulate that a confluence of trunk and upper-leg proprioceptive input establishes the basic timing of automatic, triggered balance corrections which is then preferentially weighted by vestibular modulation in muscles that prevent falling. The organisation of balance corrections around trunk inputs portrayed here would have considerable advantage for the infant learning balance control, but forces balance control centres to rely on limited sensory information related to this most unstable body segment, the trunk, when triggering balance corrections.

Notes: Abstract  The accuracy of our spatially oriented behaviors largely depends on the precision of monitoring the change in body position with respect to space during self-motion. We investigated observers’ capacity to determine, before and after head rotations about the yaw axis, the position of a memorized earth-fixed visual target positioned 21° laterally. The subjects (n=6) showed small errors (mean=–0.6°) and little variability (mean=0.9°) in determining the position of an extinguished visual-target position when the head (and gaze) remained in a straight-ahead position. This accuracy was preserved when subjects voluntary rotated the head by various magnitudes in the direction of the memorized visual target (head rotations ranged between 5° and 60°). However, when the chair on which the subjects were seated was unexpectedly rotated about the yaw axis in the direction of the target (chair rotations ranged between 6° and 36°) during the head-on-trunk rotations, the performance was markedly decreased, both in terms of spatial precision (mean error=5.6°) and variability (mean=5.7°). A control experiment showed that the prior knowledge of chair rotation occurrence had no effect on the perceived target position after head-trunk movements. Updating an earth-fixed target position during head-on-trunk rotations could be achieved through both cervical and vestibular signals processing, but, in the present experiment, the vestibular output was the only signal that had the potentiality to contribute to accurate coding of the target position after simultaneous head and trunk movements. Our results therefore suggest that the vestibular output is a noisy signal for the central nervous signal to update the visual space during head-in-space motion.

Notes: Abstract  Multivariate descriptors of sway were used to test whether altered sensory conditions result not only in changes in amount of sway but also in postural coordination. Eigenvalues and directions of eigenvectors of the covariance of shnk and hip angles were used as a set of multivariate descriptors. These quantities were measured in 14 healthy adult subjects performing the Sensory Organization test, which disrupts visual and somatosensory information used for spatial orientation. Multivariate analysis of variance and discriminant analysis showed that resulting sway changes were at least bivariate in character, with visual and somatosensory conditions producing distinct changes in postural coordination. The most significant changes were found when somatosensory information was disrupted by sway-referencing of the support surface (P=3.2·10−10). The resulting covariance measurements showed that subjects not only swayed more but also used increased hip motion analogous to the hip strategy. Disruption of vision, by either closing the eyes or sway-referencing the visual surround, also resulted in altered sway (P=1.7·10−10), with proportionately more motion of the center of mass than with platform sway-referencing. As shown by discriminant analysis, an optimal univariate measure could explain at most 90% of the behavior due to altered sensory conditions. The remaining 10%, while smaller, are highly significant changes in posture control that depend on sensory conditions. The results imply that normal postural coordination of the trunk and legs requires both somatosensory and visual information and that each sensory modality makes a unique contribution to posture control. Descending postural commands are multivariate in nature, and the motion at each joint is affected uniquely by input from multiple sensors.

Notes: Abstract  Damping characteristics of the musculoskeletal system were investigated during rapid voluntary wrist flexion movements. Oscillations about the final position were induced by introducing a load with the characteristics of negative damping, which artificially reduced the damping of the wrist. Subjects responded to increases in the negatively damped load by stronger cocontraction of wrist flexor and extensor muscles during the stabilization phase of the movement. However, their ability to counteract the effects of the negatively damped load diminished as the negative damping increased. Consequently, the number and frequency of oscillations increased. The oscillations were accompanied by phase-locked muscle activity superimposed on underlying tonic muscle activation. The wrist stiffness and damping coefficient increased with the increased cocontraction that accompanied more negatively damped loads, although changes in the damping coefficient were less systematic than the stiffness. Analysis of successive half-cycles of the oscillation revealed that the wrist stiffness and damping coefficient increased, despite decreasing muscle activation, as oscillation amplitude and velocity declined. This indicates that the inverse dependence of the damping coefficient on oscillation velocity contributes significantly to damping of joint motion. It is suggested that this property helps to offset a negative contribution to damping from the stretch reflex.

Notes: Abstract  Previous studies on how we hit moving targets have revealed that the direction in which we move our hand is continuously adjusted on the basis of the target’s perceived position, with a delay of about 110 ms. In the present study we show that the acceleration of the hand is also under such continuous control. Subjects were instructed to hit moving targets (running spiders) as quickly as possible with a rod. We found that changing the velocity of the target influenced the speed with which the rod was moved. The influence was noticeable about 200 ms after the target’s velocity changed. The extent of the influence was consistent with a direct dependence of the acceleration of the hand on the target’s velocity. We conclude that the acceleration of the hand is continuously adjusted on the basis of the speed of the target, with a delay of about 200 ms.

Notes: Abstract  We investigated force-sharing among three fingers which acted in parallel and produced ramp profiles of total force from zero to the maximal voluntary force. The feedback to the subject was provided by a visual signal on the monitor and could correspond to the sum of forces of all the fingers or to the sum of forces of two fingers, while the force of the third finger was added with a coefficient 2 or 0.5. If the subjects did not know about the distorted feedback, they showed a template-sharing pattern within the whole range of total force values. This pattern did not depend on which finger force was multiplied and by which coefficient. If the subjects knew in advance how the feedback signal would be calculated, they tried to perform the task using either only the finger whose force was multiplied by 2 or two fingers when the force of the third one was multiplied by 0.5. Further into the trial, however, they were unable to track the ramp pattern using only one or two fingers and demonstrated a search activity that could continue until the end of the trial or lead eventually to a three-finger sharing pattern similar to the template pattern used in cases of undistorted feedback. We conclude that the limited number of preferred sharing pattern within the studied task reflects an organization of the fingers into a structural unit (involving one, two, or all three fingers) by the central nervous system. The availability of structural units defines the presence of stable solutions available for the system.

Notes: Abstract  The role played by the attentional mechanisms that enable dominance of relevant objects over distractor objects was investigated by measuring changes in the kinematics of the reach-to-grasp movement. Subjects reached towards three-dimensional (3D) stimuli while attention was diverted towards distracting information consisting of either two-dimensional (2D) projected shapes or 3D objects. Movement kinematics were influenced to a greater degree when a secondary task was performed involving a 3D object rather than a 2D projected shape. When the distractor was 3D, both the reaching and the grasping components were altered but, when it was 2D only, the reaching component was modified. It is suggested that, when attention is directed towards a distractor, it is associated with interference in the kinematics of the action towards the target. Further, the nature and dimensions of the distractor selectively influence the reach or the grasp component of a prehension movement.

Notes: Abstract  To understand the internal representations used by the nervous system to coordinate multijoint movements, we examined the coordination among the body segments during reach-to-grasp movements which involve grasping by the hand and reaching by the arm and trunk. Subjects were asked to reach and grasp an object using the arm only, the trunk only, and some combinations of both arm and trunk. Results showed that kinematic parameters related to the transport component of the arm and the trunk, such as peak velocity and time to peak velocity, varied across conditions and that the coordination pattern between the arm and trunk was different across conditions. However, parameters related to the grasp component, such as peak aperture, time to peak aperture, and closing distance, were invariant, regardless of whether the hand was delivered to the target by the arm only, the trunk only, or both. We hypothesize that a hierarchy of motor control processes exists, in which the reach and grasp components are governed by independent neuromotor synergies, which in turn are coordinated temporally and spatially by a higher-level synergy.

Notes: Abstract  Electromyographic (EMG) patterns of leg muscles associated with rapid body sway were studied in relation to displacement of the center of foot pressure (CFP). Standing subjects were instructed to shift the CFP by swaying their bodies, pivoting at the ankle as rapidly and accurately as possible after an auditory signal. CFP position was designated as N when the subject maintained a relaxed bending posture and as F when a maximally forward-leaning posture was maintained. A serial, stereotyped triphasic EMG pattern was observed in the rapid shift of CFP from N to F: cessation of EMG activity in the gastrocnemius (GC) muscle was followed by a burst in the tibialis anterior (TA) muscle (acceleration phase), and then resumed discharge occurred in the GC muscle with cessation of activity in the TA muscle (deceleration and stop). When the subject shifted the CFP from N to F to different degrees, the duration and amount of EMG activity in the TA muscle during acceleration and the GC muscle in deceleration were proportionate to the amount of CFP displacement associated with forward body sway. To determine the functional roles of sensory inputs from the foot on the triphasic EMG pattern, body sway was studied under the condition of sensory block in the feet induced by ischemia from tourniquets placed bilaterally just above the ankle joints. The triphasic EMG pattern persisted during ischemia. The time of GC cessation and the onset of TA burst at acceleration remained unchanged, but the times of TA cessation and resumption of GC discharge at deceleration were altered during ischemia. Moreover, subjects were unable to stop at F and eventually fell. These results indicate that both amount and duration of EMG activity associated with rapid body sway are functions of the amount of CFP displacement. Somatic sensation from the feet is important for control of burst and cessation timing and duration in leg muscle activity.

Notes: Abstract  Three patients with cerebellar limb ataxia and three age-matched controls performed arm-pointing movements towards a visual stimulus during an experimental procedure using a double-step paradigm in a three-dimensional space. Four types of trajectories were defined: P1, single-step pointing movement towards the visual stimulus in the initial position S1; P2, double-step pointing movement towards S1; P3, double-step straight pointing movement towards the second position S2; and P4, double-step pointing movement towards S2 with an initial direction towards S1. We found that the cerebellar patients, as well as the controls, were able to modify their motor programs, but with impaired timing, severe anomalies in the direction and amplitude of the changed movement trajectories and alteration of the precision of the pointing movements.

Notes: Abstract  Young and elderly subjects performed aiming movements to a visual target with a manipulandum to determine whether the elderly reduce their reliance on visual feedback after extended practice. Reliance on visual feedback was assessed by performance on trials in which the cursor displaying arm movement was unpredictably extinguished. Movements were divided into two subcomponents: a primary, ballistic submovement and a secondary, corrective submovement. For both age groups, removal of visual feedback prior to practice resulted in a decrease in the distance covered in the primary submovement, an increase in the distance of the secondary submovement, and a decrease in endpoint accuracy. After extensive practice with the cursor present, the proportion of distance traveled with the primary submovement was again assessed under trial conditions in which the cursor randomly disappeared. Following practice, the young demonstrated that they were capable of extending the primary submovement distance closer to the target. In addition, primary submovement distance was unaffected by the removal of vision following practice. After practice the elderly did not show evidence of lengthening the primary submovement, and submovement distance and endpoint accuracy continued to be altered by the removal of vision. This suggests that, unlike the young, the elderly do not benefit from practice so that they can place a greater proportion of the movement under program control. Thus, on a relative basis, a greater proportion of their overall movement requires corrective adjustments.

Notes: Abstract  Botulinum toxin is sometimes injected into human eye muscles as an alternative to surgery in the correction of strabismus. Within minutes of botulinum injections into ungulate eye muscles, proprioceptive discharge from muscle spindles decreases dramatically. It is only over 7–48 h, however, that surgically treated strabismus patients usually show an altered proprioceptive signal about eye position, presumably from the palisade endings attached to the global multiply innervated fibers. How quickly will botulinum toxin alter proprioceptive registration of eye position in humans? First, to examine the short-term effects, we measured open-loop pointing responses (which requires knowledge of eye position) in six strabismus patients preinjection and then over a 45 min postinjection period, and in six normal controls over the same time period. Second, to examine the long-term effects, 13 strabismus patients were tested preinjection and then daily over the next 3 weeks, and three normal controls over the same time period. We compared their open-loop pointing responses with the injected eye fixating the target to the photographically determined position of the occluded other eye (a measure of where the patient would point if eye position were determined by efference, not proprioception). There were three groups of patients: esotropes with no previous injection, exotropes with no previous injection, and exotropes with previous injection. First, all patients showed significant correction of their tropias. Second, over the short-term, there was no difference in pointing responses found between the patients and the controls (t(18) = –1.427, P = 0.1706). Third, over the long-term, however, the difference between the pointing responses and eye position information was compared among the four groups across four posttests and a significant difference found (F 3,12 = 58.988, P 〈 0.00001). Only in patients with no previous injections was there altered proprioceptive feedback about eye position. Also, injections into the medial rectus induced a significantly greater proprioceptive response than those injected into the lateral rectus. In humans, botulinum toxin alters proprioception from eye muscles only over the long-term. We suggest that the toxin temporarily affects proprioceptive feedback from palisade endings.

Notes: Abstract  In cerebellar ataxia, kinematic aberrations of multijoint movements are thought to originate from deficiencies in generating muscular torques that are adequate to control the mechanical consequences of dynamic interaction forces. At this point the exact mechanisms that lead to an abnormal control of interaction torques are not known. In principle, the generation of inadequate muscular torques may result from an impairment in generating sufficient levels of torques or from an inaccurate assessment and prediction of the mechanical consequences of movements of one limb segment on adjacent joints. We sought to differentiate the relative contribution of these two mechanisms and, therefore, analyzed intersegmental dynamics of multijoint pointing movements in healthy subjects and in patients with cerebellar degeneration. Unrestrained vertical arm movements were performed at three different target movement velocities and recorded using an optoelectronic tracking system. An inverse dynamics approach was employed to compute net joint torques, muscular torques, dynamic interaction torques and gravitational torques acting at the elbow and shoulder joint. In both groups, peak dynamic interaction forces and peak muscular forces were largest during fast movements. In contrast to normal subjects, patients produced hypermetric movements when executing fast movements. Hypermetric movements were associated with smaller peak muscular torques and smaller rates of torque change at elbow and shoulder joints. The patients’ deficit in generating appropriate levels of muscular force were prominent during two different phases of the pointing movement. Peak muscular forces at the elbow were reduced during the initial phase of the movement when simultaneous shoulder joint flexion generated an extensor influence upon the elbow joint. When attempting to terminate the movement, gravitational and dynamic interaction forces caused overshooting extension at the elbow joint. In normal subjects, muscular torque patterns at shoulder and elbow joint were synchronized in that peak flexor and extensor muscular torques occurred simultaneously at both joints. This temporal pattern of muscular torque generation at shoulder and elbow joint was preserved in patients. Our data suggest that an impairment in generating sufficient levels of phasic muscular torques significantly contributes to the patients’ difficulties in controlling the mechanical consequences of dynamic interaction forces during multijoint movements.

Notes: Abstract  The objective of this study was to develop a quantitative method to assess muscle spindle function. Three groups of subjects were studied: ten young and healthy subjects, 15 older subjects with diabetic neuropathy, and 15 age-matched controls. All subjects performed an ankle-movement matching task with and without muscle vibration. Input from the plantar cutaneous mechanoreceptors was minimized by using a foot-clamping device. The younger subjects tracked the movement very well, but vibration had a significant effect on their performance (P 〈 0.001). Similar results were seen in the older control subjects, but they were less successful in tracking movement and slightly less affected by vibration. The neuropathic subjects had the most difficulty tracking, and vibration had only a small but still significant effect on their performance. The interaction between the group and the vibration effect was highly significant (P 〈 0.001), indicating that the performance of the control subjects changed to a greater degree in the presence of vibration than the performance of the subjects with diabetic neuropathy. Muscle spindles are the primary receptors that are involved in the change in tracking performance when vibration is added during an ankle-movement matching task, and we therefore conclude that the procedure described provides a quantitative evaluation of muscle spindle function.The results demonstrate that diabetic neuropathy degrades muscle sensory function, which may contribute to the impaired balance and unsteadiness of gait that has been observed in diabetic neuropathy.

Notes: Abstract  Five subjects made rapid, discrete elbow flexion movements over different distances, against different inertial loads, as well as under distance and load combinations that kept movement time constant. The results demonstrated that an increase in peak movement velocity was associated with an increase in the temporal symmetry ratio of the movement (acceleration time divided by deceleration time), as well as with an increase in both agonist electromyographic (EMG) burst duration and antagonist EMG latency. Since an increase in peak movement velocity is associated with faster agonist muscle shortening, as well as with faster stretching of the antagonist muscle, we hypothesize that the velocity-related changes in movement symmetry can be viewed as, at least partially, a consequence of muscle viscosity. Viscosity increasingly resists the shortening agonist and assists the lengthening antagonist when movement velocity increases. Therefore, the agonist muscles require more time to produce the required impulse, while the antagonist muscle can brake the movement in a shorter period of time. In order to test the hypothesis that viscosity is responsible for the velocity-associated changes in the symmetry ratio, we performed a second experiment with distance and load combinations identical to those of the first experiment, but with different external viscous loads, which resisted the slower and assisted the faster movements. The results demonstrated that the movements became more symmetrical in the presence of the viscous load. There were also changes in agonist duration and antagonist latency. We conclude that changes in the symmetry associated with changes in movement velocity may be due to the effects of either muscle viscosity or changes in how muscles are activated to account for differences in viscous force.

Notes: Abstract  Experiments on visual attention have employed both physical cues and verbal instructions to enable subjects to allocate attention at a location that becomes relevant within a perceptual or motor task some time later (cue lead time, CLT). In this study we have used valid visual peripheral cues (CLT between 100 and 700 ms) to indicate the direction and location of the next saccade. A cue is considered valid or invalid if its meaning with respect to the next saccade is correct or incorrect. A cue is called an anti- or pro-cue if the side of its presentation is opposite to or the same as the direction of the saccade required on a given trial. Correspondingly, a saccade is called an anti- or pro-saccade if it is directed to the side opposite to or the same as the stimulus presentation. A condition in which the cue and the stimulus are presented on opposite sides provides a simple way of dissociating voluntary attention allocation from automatic orienting. This paper considers the anti-cue pro-saccade task: the subjects were instructed to use the cue to direct attention to the opposite side, i.e. the location, where on valid trials the saccade target would occur. In the companion paper we have used the same physical condition, but we have reversed the instructions as to saccade direction and we have reversed the meaning of the cue, i.e. we designed a pro-cue anti-saccade task. In this first paper, the saccadic reaction times (SRTs) of pro-saccades of five adult subjects were measured in the gap paradigm (fixation point offset precedes target onset by 200 ms). With a CLT of 100 ms, valid anti-cues reduced the number of express saccades (i.e. saccades with SRTs in the range 80–120 ms) significantly compared with the control values (no cues). Valid anti-cues with increasingly long CLTs (100–700 ms) resulted in an increasing incidence of anticipatory saccades and saccades with longer SRTs (more than 120 ms), while the frequency of express saccades remained below the control value. When cue and saccade target were dissociated in location or in both location and direction, the effects of the cueing revealed a much lower spatial selectivity as compared to the effects that have been described for voluntary attention allocation by means of central cues. The results suggest that voluntary allocation of attention and cue-induced automatic orienting not only have different time courses but also have opposite effects on the generation of express saccades, and different spatial selectivities. A possible neuronal basis of these results is discussed considering related findings from electrophysiological studies in monkeys.

Notes: Abstract  Disparities in load stiffness were used to differentiate and characterize pinch-force, finger-span, and pinch-effort matching in two experiments. All subjects squeezed a spring-loaded manipulandum in each hand using three-finger pinch. Subjects in the first experiment were instructed explicitly to match one of the three continua. Subjects matching force or span were told to attend carefully to sensations from the hand or arm and to ignore differences in the effort required to make the sensations equal. They had to achieve and hold a particular target force with the reference hand and then match force or span with the opposite hand, usually against a spring with a different stiffness. These subjects were given as much time as necessary to make their matches and were told which hand was serving as the reference in each trial. Effort-matching subjects were told to ignore peripheral sensations and to match effort or motor commands. These subjects were not told which hand was the reference and were given only 1 s to make a match, so they made matches by rapidly squeezing both manipulanda simultaneously and, presumably, with the same voluntary motor command. The matching behaviors of the three groups were clearly distinguishable and were consistent with instructions. Results were similar whether different subjects were assigned different instructions or the same subjects performed all three match types. In a second experiment, naïve subjects were given purposely ambiguous instructions without reference to a specific continuum and had no time or accuracy constraints. Subjects produced the same three sensorimotor behaviors obtained with explicit instructions, showing that the different behaviors were not artifacts of strict protocols. Taken together, the results show that force, span, and effort are distinct sensorimotor continua that can be judged reliably.

Notes: Abstract  This paper describes the transport and grasp kinematic parameters associated with four initial hand postures (palm flat and thumb against the hand, palm flat and thumb extended laterally, index and thumb in opposition, and index and thumb in opposition and elbow flexed 90°). A group of healthy adult subjects reached for and picked up a wooden dowel placed midsagittally, at one of three distances (20 cm, 25 cm and 30 cm). The initial posture of the hand and arm altered transport (peak velocity and peak negative acceleration) as well as grasp (peak angle and time to peak angle) parameters, particularly when the elbow was flexed 90°. The pattern of results was reproduced in a pointing paradigm. The findings are discussed in the context of joint space models of reaching.

Notes: Abstract  CO2 laser pulses selectively excite A-δ and C mechano-thermal nociceptors in the superficial layers of the skin. To study the jaw-opening reflex elicited by a purely nociceptive input, we delivered laser pulses to the perioral region in 15 subjects. Sensory threshold was very low (9 mJ/mm2). High-intensity noxious laser pulses (more than 4 × sensory threshold) evoked a single phase of electromyogram suppression (laser silent period, LSP) at an onset latency of 70 ms in the contracted masseter and temporal muscles, bilaterally. Even maximum-intensity laser pulses failed to activate the suprahyoid muscles. The recovery curves to paired laser stimuli showed that at short interstimulus intervals the test LSP was strongly suppressed. At about 380 ms it recovered to 50%, i.e. its recovery curve resembled that of the masseter late silent period after electrical mental nerve stimulation (SP2). In experiments studying the interaction with heterotopic stimuli and non-nociceptive responses, chin-taps or electrical shocks delivered to the supraorbital, infraorbital or mental nerves before laser stimulation strongly suppressed the LSP. A preceding perioral laser pulse strongly suppressed the masseter SP evoked by supraorbital stimulation and the SP2 evoked by mental stimulation, but left SP1 unaffected. We conclude that the perioral A-δ fibre input elicits a jaw-opening reflex simply by inhibiting the jaw-closers. The LSP response is mediated by a multisynaptic chain of brainstem interneurons and shares with the masseter SP2 part of the central circuit in the ponto-medullary region. We also propose that a common centre processes the various inputs for jaw opening.

Notes: Abstract  Isometric force-related functional magnetic resonance imaging (fMRI) signals from primary sensorimotor cortex were investigated by imaging during a sustained finger flexion task at a number of force levels related to maximum voluntary contraction. With increasing levels of force, there was an increase in the extent along the central sulcus from which a fMRI signal could be detected and an increase in the summed signal across voxels, but these parameters were related in such a way that the signal from each voxel was similar for each level of force. The results suggest that increased neuronal firing and recruitment of corticomotor cells associated with increased voluntary isometric effort are reflected in an expansion of a relatively constant fMRI signal over a greater volume of cortex, rather than an increase in the magnitude of the response in a particular circumscribed region, possibly due to perfusion of an increase in oxygen-enriched blood over a wider region of the cortex.

Notes: Abstract  This purpose of this study was to examine the spatial coding of eye movements during static roll tilt (up to ±45°) relative to perceived earth and head orientations. Binocular videographic recordings obtained in darkness from eight subjects allowed us to quantify the mean deviations in gaze trajectories along both horizontal and vertical coordinates relative to the true earth and head orientations. We found that both variability and curvature of gaze trajectories increased with roll tilt. The trajectories of eye movements made along the perceived earth-horizontal (PEH) were more accurate than movements along the perceived head-horizontal (PHH). The trajectories of both PEH and PHH saccades tended to deviate in the same direction as the head tilt. The deviations in gaze trajectories along the perceived earth-vertical (PEV) and perceived head-vertical (PHV) were both similar to the PHH orientation, except that saccades along the PEV deviated in the opposite direction relative to the head tilt. The magnitude of deviations along the PEV, PHH, and PHV corresponded to perceptual overestimations of roll tilt obtained from verbal reports. Both PEV gaze trajectories and perceptual estimates of tilt orientation were different following clockwise rather than counterclockwise tilt rotation; however, the PEH gaze trajectories were less affected by the direction of tilt rotation. Our results suggest that errors in gaze trajectories along PEV and perceived head orientations increase during roll tilt in a similar way to perceptual errors of tilt orientation. Although PEH and PEV gaze trajectories became nonorthogonal during roll tilt, we conclude that the spatial coding of eye movements during roll tilt is overall more accurate for the perceived earth reference frame than for the perceived head reference frame.

Notes: Abstract  To examine the effects of smooth-pursuit eye movements on the initiation of saccades, their latency was measured when subjects initially fixated or pursued a target. In half of the block of trials, the fixation or pursuit target was extinguished 200 ms before the saccade target was illuminated (gap trials). Reduction of the mean saccade latency in the gap trials (the “gap effect”) was evident even when the subjects were pursuing a moving target, consistent with previous observations. The effect of pursuit direction on saccade latency was also examined. Saccades in the same direction as the preceding pursuit (forward saccades) had shorter latencies than those in the opposite direction (backward saccades). This asymmetry was observed in both the gap and nongap trials. Although the forward-backward asymmetry was much smaller than the “gap effect”, it was statistically significant in six of eight cases. These results suggest that the preparation of saccades is affected by smooth-pursuit eye movements.

Notes: Abstract  Two-limb coordination of homologous and non-homologous effectors was examined during isofrequency (1:1) and multifrequency (2:1) conditions. The coordination patterns involved flexion and extension movements in the sagittal plane and were performed under unloaded and single-limb (right arm) loaded conditions. Previous studies suggested that the lower degree of 1:1 synchronization observed during nonhomologous as compared to homologous coordination results from natural differences in biophysical (inertial) properties. Elaborating on this idea, adding weight to the right arm was hypothesized to modulate its inertial characteristics, rendering homologous limbs more dissimilar and nonhomologous limbs more similar by enhancing and decreasing their inertial differences, respectively. Therefore, the observations made during unloaded conditions were predicted to be completely reversed during loaded conditions. Findings revealed that during 1:1 coordination (experiment 1) single-limb loading resulted in a decreased relative phase stability, whereas relative phase accuracy depended upon the limb combination. In particular, phase-locking was more accurately maintained for loaded homologous than for nonhomologous limbs, whereas loading the nonhomologous limbs resulted in a deterioration of the quality of synchronization. These findings suggest that there is an additional explanation of differential coordination capabilities among limb combinations. It is hypothesized that the neural networks subserving the control centers of the homologous limbs are more tightly connected than those of the nonhomologous effectors, allowing 1:1 synchronization to be more successfully preserved in the face of (load) perturbations. During 2:1 coordination (experiment 2), the loading procedure disturbed the coordination dynamics across all limb combinations. That no differential effect of loading on effector combination was observed is possibly a result of the fact that only an initial level of practice was studied in which optimal relative phase dynamics are still being explored for both homologous and nonhomologous limbs.

Notes: Abstract  The purpose of this study was to identify the brain regions activated in relation to oculomotor sequence learning. Nine healthy subjects participated in the study, which consisted of three positron emission tomography scans. In the initial learning task, subjects were instructed to track a sequence of seven successive positions of visual targets and to memorize the order of the targets as well as their spatial locations. In the saccade task, subjects were instructed to track visual targets presented at random locations. In the control task, subjects were instructed to gaze at a fixation point. Fields showing significant regional cerebral blood flow change were determined from task-minus-control subtraction images. We determined that fields in the pre-supplementary motor area (pre-SMA), the intraparietal cortex, and the prefrontal cortex were activated not only in the learning-minus-control images but also in the learning-minus-saccade images. Although prefrontal and parietal activations were bilateral, pre-SMA activation was confined to the left hemisphere. The results indicate that these fields function as a part of the neural network involved in the learning of sequential saccadic eye movements.

Notes: Abstract  Subjects made a fast elbow extension movement to designated target in response to a go signal. In 45% of trials a stop signal was presented after the go signal, to which subjects were asked to stop the movement as rapidly as possible. The interstimulus interval (ISI), or time interval between the go and stop signals, was randomly varied between 0 and 200 ms. Electromyographic (EMG) activity was recorded from biceps brachii and triceps brachii. Subjects could sometimes completely inhibit initiation of the movements when the ISI was 0 ms, but could rarely do so when the ISI exceeded 100 ms. For responses that were initiated but stopped on the way, the amplitude of the movement decreased linearly as the time interval (=modification time) from the stop signal to EMG onset increased. The peak velocity increased linearly as the movement amplitude increased. This tendency was similar to those previously reported in step-tracking movements with various amplitudes. In spite of the similarity in the kinematics of the movement, the EMG pattern was different from that of step-tracking movement. While the initial agonist burst (AG1) decreased linearly after the modification time exceeded 100 ms, the antagonist burst (ANT) increased compared with the go trial for the modification time from 0 to 200 ms and decreased after the modification time exceeded 300 ms. This change of activation is analogous to functional modification of middle-latency reflex EMG response to load, or cutaneous perturbation. In conclusion, it is suggested that adaptive mechanisms, which would functionally modify the reflex responses, are also continuously working during voluntary movements in response to sudden changes in environmental information.

Notes: Abstract  Information from the auditory and visual systems converges in the nervous system with physiological and behavioral consequences. Most of our knowledge about the rules governing such convergence has been obtained in experiments where the strength or the timing of the individual auditory and visual stimuli has been varied. Relatively little attention has been paid to the spatial relationship between different modalities of stimuli in multisensory experiments. We studied saccadic reaction times of human subjects to bimodal auditory and visual stimulus presentations under two conditions: first, with the targets spatially coincident and, second, with various degrees of spatial separation or disparity. In the first experiment, we found that the saccadic reaction times were consistently shorter than would be predicted by independent processing of information about the visual and auditory targets. These results suggest convergence of multimodal information at one or more loci within the nervous system. In the second experiment, we found that saccadic latency gradually increased as spatial distance between the auditory and visual targets increased. Evidence for neural summation was found over a wide range of spatial disparities. These results suggest that multisensory information can be integrated and have significant influences on behavior over a surprisingly large range of spatial disparity.

Notes: Abstract  Dynamic posturography by measurement of center of pressure (COP) is a widely employed technique for evaluating the vestibular system. However, the relationship of COP motion to vestibulo-ocular reflex (VOR) function and image stability on the retina has not been determined previously. To assess these relationships, we report gaze, head, and trunk stability during dynamic posturography in 11 normal volunteers, 7 subjects with unilateral vestibular lesions, and 3 subjects with bilateral vestibular lesions. Posturographic tasks consisted of standing still and standing on a platform that was sliding (0.2 Hz), tilting (0.1 Hz), or covered with a foam cushion 6 cm thick while tilting (0.1 Hz). Each perturbation was imposed in the anterior-posterior and repeated in the medial-lateral direction, in both light and darkness. Subjects viewed (or in darkness remembered) a target located 50, 100, or 500 cm distant. COP, angular eye position, and angular and linear orbit and trunk positions were measured using magnetic search coils and flux gate magnetometer sensors. With the target visible, the velocity of image motion on the retina was on average always less than 1°/s, well within the range consistent with high visual acuity. In darkness, gaze velocity increased for normal and vestibulopathic subjects. During tilt, vestibulopathic subjects had a significantly greater gaze velocity than controls. Gain of the angular VOR (eye velocity/head velocity) was significantly lower in darkness than in light and in vestibulopathic as compared to control subjects. Gain of the VOR was significantly correlated with gaze instability, but variation in VOR gain accounted for only 20–40% of the variance. In darkness, the velocity of the COP was significantly greater in vestibulopathic than control subjects for every condition tested. In light, this difference was small and often not significant. Although spectral analysis of the COP indicated frequencies above 1 Hz that were not observed in motion of the trunk and orbit, root mean square (RMS) velocities of the trunk and orbit in the horizontal plane were higher in darkness and in vestibulopathic subjects, mirroring COP findings. Only in vestibulopathic subjects tested in darkness was there a correlation between COP velocity and gaze velocity; COP velocity was otherwise uncorrelated with gaze. Gaze velocity was greater with near than with distant targets. Vertical VOR gain was higher with near targets. No other significant effects of target distance were found. Head movement strategy, VOR gain, and COP were all unaffected by target proximity. These data show that gaze velocity measurements during dynamic posturography in darkness are sensitive to vestibular loss. With a visible target, both COP and gaze stability of vestibulopathic subjects are difficult to distinguish from normal. During visual feedback, it is likely that image stabilization over the range of frequencies tested is achieved through better head stability and through visual tracking, allowing vestibulopathic subjects to maintain adequate visual acuity.

Notes: Abstract  Eye-head coordination during saccadic gaze shifts normally relies on vestibular information. A vestibulo-saccadic reflex (VSR) is thought to reduce the eye-in-head saccade to account for current head movement, and the vestibulo-ocular reflex (VOR) stabilizes postsaccadic gaze while the head movement is still going on. Acute bilateral loss of vestibular function is known to cause overshoot of gaze saccades and postsaccadic instability. We asked how patients suffering from chronic vestibular loss adapt to this situation. Eye and head movements were recorded from six patients and six normal control subjects. Subjects tracked a random sequence of horizontal target steps, with their heads (1) fixed in primary position, (2) free to move, or (3) preadjusted to different head-to-target offsets (to provoke head movements of different amplitudes). Patients made later and smaller head movements than normals and accepted correspondingly larger eye eccentricities. Targeting accuracy, in terms of the mean of the signed gaze error, was better in patients than in normals. However, unlike in normals, the errors of patients exhibited a large scatter and included many overshoots. These overshoots cannot be attributed to the loss of VSR because they also occurred when the head was not moving and were diminished when large head movements were provoked. Patients’ postsaccadic stability was, on average, almost as good as that of normals, but the individual responses again showed a large scatter. Also, there were many cases of inappropriate postsaccadic slow eye movements, e.g., in the absence of concurrent head movements, and correction saccades, e.g., although gaze was already on target. Performance in patients was affected only marginally when large head movements were provoked. Except for the larger lag of the head upon the eye, the temporal coupling of eye and head movements in patients was similar to that in normals. Our findings show that patients with chronic vestibular loss regain the ability to make functionally appropriate gaze saccades. We assume, in line with previous work, three main compensatory mechanisms: a head movement efference copy, an active cervico-ocular reflex (COR), and a preprogrammed backsliding of the eyes. However, the large trial-to-trial variability of targeting accuracy and postsaccadic stability indicates that the saccadic gaze system of patients does not regain the high precision that is observed in normals and which appears to require a vestibular head-in-space signal. Moreover, this variability also permeates their gaze performance in the absence of head movements.

Notes: Abstract  Movements have been described as being governed by a speed-sensitive (SS) or speed-insensitive (SI) strategy. The SS strategy is used when the subject controls, either explicitly or implicitly, movement speed or time. In contrast, the SI strategy is utilized when there is no intention or requirement to control movement speed. The different strategies demonstrate a specific relationship between torque trajectories and muscle activity. The purpose of this study was to determine the effect of accuracy and force level on strategy selection. Ten healthy adults were instructed to generate isometric pulse contractions of the right soleus at 20%, 40%, and 60% of maximum voluntary contraction (MVC) to reach five target sizes of percentage MVC (4%, 8%, 12%, 16%, 20%). The following results were observed: (1) there was no difference in time to peak force, peak dF/dt, slope of force, and electromyographic (EMG) measures between the 12%, 16%, and 20% target sizes; (2) differences were noted, however, between the 12%, 16%, and 20% targets and the smaller targets; (3) for the dependent measures there were significant differences between each force level. No difference between the larger targets implies that subjects do not need to implement a strategy and suggests an upper limit to the dual-strategy hypothesis. The difference between the smaller and larger targets and the difference between the force levels is indicative of an SS strategy. When asked to use different force levels, subjects controlled the rate of rise of force and regulated time to peak force. Between target sizes, force and time were modulated equally.

Notes: Abstract  Latencies of eye movements to peripheral targets are reduced when there is a short delay (typically 200 ms) between the offset of a central visual fixation point and the target onset. This has been termed the gap effect. In addition, some subjects, usually with practice, exhibit a separate population of very short latency saccades, called express saccades. Both these phenomena have been attributed to disengagement of visual attention when the fixation point is extinguished. A competing theory of the gap effect attributes it to disengagement of oculomotor fixation during the temporal gap. It is known that auditory targets are effective in eliciting saccadic eye movements, and also that covert attention operates in the auditory modality. If the gap effect and express saccades are due to disengagement of spatial attention, both should persist in the auditory modality. However, fixation of gaze is largely under visual control. If the gap effect results from disengagement of fixation, then at least a reduced effect should be seen in the auditory modality. Human subjects performed the gap task and a control task in the dark, using auditory fixation points and saccadic targets, on five successive days. Despite this practice, express saccades were not observed. There was a reliable gap effect, but the reduction in saccadic latency was only 17 ms, compared with 32 ms for the same subjects in the visual modality. This suggests that about half the gap effect is due to disengagement of visual fixation. The remainder was not due to non-specific warning effects and could be attributed to offset of the auditory fixation stimulus.

Notes: Abstract  The motor performance of seven patients with Parkinson’s disease and seven control subjects was tested in a choice reaction aiming task. The subjects were instructed to aim as fast and as accurately as possible to a light stimulus, which defined one of eight possible target positions. In order to reach the targets, elbow flexions had to be combined with forearm supinations or with forearm pronations. For single-joint movements, forearm supinations or pronations were executed faster than the long elbow flexions in both groups. In the double-joint movements of the control group, the flexion movement times (flex.MTs) and the supination movement times (sup.MTs) or pronation movement times (pron.MTs) were similar to the MTs of the corresponding single-joint movements. MTs of parkinsonian patients were significantly longer than those of control subjects. MTs were most increased in the forearm supination and forearm pronation of double-joint movements. In contrast to the controls, sup.MT and pron.MT were significantly increased in double-joint movements as compared to single-joint movements. The variations in the flex.MT and sup.MT of the double-joint movements neither correlated for a control subject nor for a parkinsonian patient. For controls, the independent MTs in double-joint movements cannot be explained by minimal principles (minimum energy, minimal torque change), but suggest that two separate motor programs are superimposed. In Parkinson’s disease, there seems to be a deficit in superimposing two separate motor programs.

Notes: Abstract  The transport and grip components are two controlled components of a prehensile movement. These components are coordinated so that objects of varying size and shape resting in diverse locations can be grasped easily. It has been suggested that the timing between these two components is a specified parameter, although the origin of such timing is unknown. The present study examines the interdependency of the reach and grasp components when the transport component is modified by placing an obstacle of varying height (9 cm and 11 cm) in the hand path between the starting position and the target object location. Subjects were asked to reach over a Plexiglas barrier and grasp a 2-cm dowel. To reach the object, the subject had to elevate the hand. At issue in this experiment is whether changes in hand path trajectory caused by obstacle avoidance produce corresponding changes in the kinematics of grip aperture. The findings showed that reaching in the presence of an obstacle resulted in the prolongation of most transport component time parameters except peak acceleration and a few amplitude parameters. Changes in the transport component also produced systematic prolongation in all time parameters of grip kinematics, including grip closure time. Temporal prolongation was also reflected in a significant decrease in grip opening and closing velocity; only relative time-to-peak closing velocity was maintained. Closure distance and maximum grip aperture were smaller for the obstacle conditions. Together with the observed smaller variability for the distance to peak aperture, these findings suggest that spatial localization of the hand aperture is an important prehensile movement control feature. Parameterization processes for the grip component are closely linked to those of the transport component, and their organization appears to be interdependent.

Notes: Abstract  We have investigated the coordination of hand aperture with the spatial path of hand transport in prehensile movement by comparing straight prehensile movements with curved movements, in which subjects had to pass over a “via point” marked on the worksurface before picking up an object in the target location. Spatial plots of hand aperture against hand transport showed that the preshaping of the hand to prepare an appropriate grasp was delayed in the curved movements relative to the straight movements, with most of the preshaping of the hand occurring after passing the via point, even when the via point occurred late in the course of the movement. The postponement of hand preshaping was apparently not due to subjects’ segmenting the movement into two completely separate portions preceding and following the via point, since some degree of hand opening often occurred before the via point. We suggest that the delay in hand opening in curved movements involves a scheduling process, which uses information about hand transport to set an appropriate hand aperture.

Notes: Abstract  Transient visual field defects (VFDs) and phosphenes were induced in normal volunteers by means of transcranial magnetic stimulation (TMS) using a circular magnetic coil of 12.5 cm diameter placed with its lower rim 2–4 cm above the inion in the midline. Subjects had to detect small, bright dots presented randomly for 14 ms in one of 60 locations on a computer screen resulting in a plot of the central 9° of the visual field. In 8 of 17 subjects, transient VFDs were inducible at peak magnetic field strenghts of 1.1–1.4 T. In the central 1–3°, detection of targets was impaired in both the upper and lower visual field, whereas at 4–9° large parts of only the lower visual field were affected with a sharp cut-off along the horizontal meridian. Targets at 1° in the lower field were affected with lower TMS intensities than corresponding locations in the upper or peripheral locations in the lower field. Detection of central targets was affected at more caudal stimulation sites than detection of peripheral targets. Phosphenes were elicitable in 14 of 17 subjects at clearly lower field strengths of 0.6–1.0 T. Many subjects perceived chromatophosphenes. From a discussion of the literature on patients with VFDs and the known topography of the human visual system, it is concluded that the transient VFDs at 1–3° are probably due to stimulation of both striate cortex (V1) and extrastriate areas (V2/V3), while VFDs in the lower visual field at eccentricities 4–9° are due to stimulation of V2/V3 but not V1.

Notes: Abstract  Studies of rapid, single degree-of-freedom movements have shown different changes in electromyographic patterns for movement tasks that appear very similar (e.g., movements over different ranges of distance). However, it is not clear whether these differences are a result of joint-specific control schemes or whether they are instead due to the limited range of task parameters studied relative to the mechanical constraints of each joint (e.g., short compared with long movements relative to the range of motion of a particular joint). In this study, we measured and compared the kinematic trajectories and electromyograms recorded during various movement tasks at the wrist, elbow, and ankle. Subjects performed movements over a wide range of distances “as fast as possible,”“at a comfortable speed,” and against two inertial loads (at the elbow only), and they performed movements over a fixed distance at three different speeds at the wrist and ankle. For fast movements we show that, in spite of some joint-specific differences, the basic pattern of electromyographic (EMG) modulation is similar at all three joints; for example, the agonist EMG burst transitions from a fixed duration to an increasing duration with increasing movement distance at all three joints. Moreover, the distance at which this transition occurs in one joint relative to the distance at which this transition occurs in the other two joints is consistent across subjects. The transition occurs at the shortest distance at the ankle and the longest distance at the wrist. In general we suggest that the data are consistent with a single set of control rules applied at all three joints, with the biomechanical constraints at each joint accounting for the differences in the EMG and kinematic patterns observed across joints.

Notes: Abstract  Investigations of pain using functional imaging techniques have revealed an extensive central network associated with nociception. This network includes the thalamus, insula, prefrontal cortex and anterior cingulate cortex (ACC) as well as the somatosensory cortices. Positron emission tomography (PET) of regional cerebral blood flow (rCBF) has demonstrated activation of the ACC during cognitively challenging tasks such as the Stroop interference task and divided attention. One interpretation of this research is that ACC is involved in the general features of attention and that it does not play a specific role in pain processing per se. Three-dimensional PET imaging provides a method for assessments of rCBF in a single individual during multiple tasks. In addition, coregistration of PET and magnetic resonance (MR) images allows for better localisation of the PET signals so that differences in cortical activation sites can be more accurately determined. This approach was used to assess rCBF during the experience of pain by subtracting images collected during heat from those during noxious heat stimulation. Two regions of the ACC had elevated rCBF, one in the perigenual region and one in the mid-rostrocaudal region (i.e. midcingulate cortex). During the execution of the Stroop task, the group result showed the midcingulate region overlapping with the site seen during the experience of pain. This group result, however, was not confirmed in the individual subject analysis, which revealed widespread and independent areas of ACC response to pain and Stroop. It is concluded that the ACC contributes to multiple cognitive procedures. It is inadequate to describe the primary contribution of ACC to pain processing as “attention” because it is unlikely that the multiple small and independent activation sites produced by pain and Stroop subserve attentive processing throughout the brain.

Notes: Abstract  Rhythmic interlimb coordination is characterized by attraction to stable phase and frequency relations. Sudden, unintended transitions between such coordination patterns have been observed in iso- and multifrequency tasks when movement frequency was gradually increased. These transitions have been accounted for by modeling the two limbs as nonlinearly coupled oscillators. The prevailing form of the coupling function is based on time derivatives, but an alternative formulation can be derived by incorporating time delays. These time delays may be related to the neurophysiological delays associated with the use of kinesthetic afferences. The two ways of deriving coupling functions for interlimb coordination allow for different predictions with respect to the effects of movement frequency and amplitude on the strength of interaction between the limbs. In the current experiment, the effects of amplitude and frequency were dissociated experimentally, so as to arrive at an empirically motivated choice between the two ways of formalizing interlimb coupling. Subjects tapped the polyrhythm 2:3 at five different frequencies under three amplitude conditions. Whereas no effects of amplitude were observed, the strength of interaction between the hands decreased with increasing movement frequency. These results support the time-delay version of the model, in which differential (loss of) stability of coordination modes results from differential dependence on movement amplitude, but overall coupling strength is related reciprocally to movement frequency squared. This version of the model was related tentatively to three proposed aspects of interlimb coordination: (1) neurophysiological delays associated with the use of kinesthetic afferences; (2) rate-dependent decrease in pattern stability; and (3) differential entrainment influences of kinesthetic signals.

Notes: Abstract  The reflex responses to brisk, ramp stretch perturbations of the human flexor pollicis longus muscle (FPL) were recorded during isometric and slow concentric or eccentric contractions at similar levels of muscle excitation. The subjects flexed their thumb to push down against a thumb-rest, whose position was controlled by a servo-controlled motor. In different runs, the stretch perturbations were imposed when the thumb-rest was stationary (isometric) or was flexing or extending the interphalangeal joint of the thumb at a constant velocity, i.e. during concentric or eccentric contractions of FPL. The latency of the most prominent component of the electromyographic reflex in the isometrically contracting muscle was about 60 ms, measured from the command signal. The amplitude of this response was sharply reduced during the non-isometric contractions. While not dependent on the direction, this modulation of the reflex response increased with the speed of active movement of the interphalangeal joint (flexion or extension). The response was greatly reduced during concentric or eccentric movements as slow as 1.6 mm·s–1 (approximately 5°·s–1 at the joint). When the force rather than the position of the thumb-rest was servo-controlled, the stretch response to perturbation again diminished with speed in a self-paced flexion task, compared with an isometric “hold” condition.

Notes: Abstract  We investigated intermanual transfer and long-term retention of practice-related perceptual learning in the domain of tactile hyperacuity. Subjects discriminated a row of three dots in which the central dot was offset laterally from a row without such offset. Performance at the right index fingerpad improved with practice. Practice effects transferred essentially completely to the left index fingerpad. When tested some months later at the right index fingerpad, long-term retention of learning was limited and further practice was required to stabilize discrimination thresholds. Intermanual transfer of tactile learning appears to be a general phenomenon, while long-term retention appears to be limited in hyperacuity tasks.

Notes: Abstract  Prior studies have shown that procedural learning is severely impaired in patients with diffuse cerebellar damage (cortical degeneration) as measured by the serial reaction time task (SRTT). We hypothesize that focal cerebellar lesions can also have lateralized effects on procedural learning. Our objective was to assess the effects of focal cerebellar lesions in procedural learning as measured by the SRTT. We studied 14 patients with single, unilateral vascular lesions in the territory of the posterior-inferior or superior cerebellar artery, who were compared with ten age- and sex-matched controls in a one-handed version of the SRTT. Patients with lesions at any other level of the brain or posterior fossa were excluded by cranial magnetic resonance imaging. Our results show that patients do not acquire procedural knowledge when performing the task with the hand ipsilateral to the lesion, but show normal learning with the contralateral hand. No correlation was found with the side, size, or vascular territory of the lesion. We conclude that procedural learning is impaired in hemispheric cerebellar lesions and involves only the hand ipsilateral to the lesion, which suggests a critical role for the cerebellum and/or crossed cerebellar-prefrontal connections in this type of learning.

Notes: Abstract  This study assessed the reach to grasp movement and its adaptive response to a simultaneous perturbation of object location and size. The aim was to clarify the means by which integration between the neural pathways modulating transport and manipulation is achieved. Participants (n = 11) were required to reach 30 cm to grasp a central illuminated cylinder of either small (0.7 cm) or large (8 cm) diameter. For a small percentage of trials (20/100) a visual perturbation was introduced unexpectedly at the onset of the reaching action. This consisted of a shift of illumination from the central cylinder to a cylinder of differing diameter (large in session A; small in session B) that was positioned 20° to the left (n = 10 trials) or to the right (n = 10) of the central cylinder. The subject was required to grasp the newly illuminated cylinder. Movement duration for these “double” (position and size) perturbed trials was much longer than those of control trials to the central cylinder (session A: by an average of 250 ms; session B: 180 ms), and the increased values were much greater than those reported previously in “single” perturbation studies where either size or location of the object was perturbed. Initial signs of a response to the “double” perturbation were seen almost simultaneously in the transport parameter of peak arm deceleration and in the manipulation parameter of maximum grip aperture, but these changes were not evident until more than 400 ms after movement onset, a response onset much later than that found in “single” perturbation studies. It is proposed that the visual change resultant from the double perturbation activates integration centres that at first gate the flow of information to the parallel channels of transport and manipulation. Following processing of this information, these centres act to instigate a synchronised and coordinated response in both components. These results add support to the existence of neural centres dedicated to the integration of parallel neural pathways, and which exercise flexibility in the degree to which these components are “coupled” functionally.

Notes: Abstract  The phase of the angular vestibulo-ocular reflex (VOR) is subject to adaptive control. We had previously found that adapting the phase of the VOR also produced changes in drift on eccentric gaze-holding, implying a change in the time constant of the velocity-to-position neural integrator. Here we attempted to dissociate changes in gaze-holding drift from changes in the phase of the VOR. In normal human subjects, for 2 h, we alternated 5 min of VOR phase adaptation (sinusoids, 0.2 Hz) with 5 min of making saccades in the light with the head stationary. Afterwards, changes in VOR phase were the same (32% of requested) as those obtained with 1 h of phase adaptation alone, but changes in drift following saccades were much smaller than those found after phase adaptation alone (0.8°/s compared with 5°/s). When measuring drift after VOR steps, however, the changes were closer to those found after phase adaptation alone (3.8°/s). To test the relationship between gaze-holding drift after VOR steps and adaptive changes in VOR phase, we alternated sinusoidal VOR phase adaptation with normal VOR steps in the light. In this paradigm, the adaptive change in VOR phase was about the same as with phase-adaptation alone (35%), but there was now little drift after saccades (1.9°/s) or after VOR steps (0.7°/s). We conclude that the state of the velocity-to-position neural integrator can be altered selectively and rapidly depending upon the task required. Such context-specific adaptation is advantageous, because it allows adjustment of the phase of the VOR without degrading the ability to hold eccentric fixation.

Notes: Abstract  We examined the lower-limb electromyographic (EMG) activity from a patient with clinically complete spinal cord injury during orthotic gait. A newly developed gait orthosis was used to obtain bipedal locomotion. The surface EMG data during the gait together with the biomechanical variables were collected by way of a radio EMG system. A cyclic EMG activation pattern corresponding to the gait cycles were observed in each of the paralyzed lower-limb muscles during the orthotic gait. Although the EMG activation did not seem to contribute toward generating the gait, it showed some similarities to that of the infant stepping or immature gait. These results might be regarded as one of the indirect pieces of evidence that suggest the existence of a spinally originating motor mechanism underlying human locomotion.

Notes: Abstract  Cerebral blood flow studies in humans suggest that the anterior cingulate cortex (ACC) could be involved in eye movement control. In two patients with a small infarction affecting the posterior part of this area (on the right side) and in ten control subjects, we studied several paradigms of saccadic eye movements: gap task, overlap task, antisaccades (using either a 5° or 25° lateral target), memory-guided saccades with a short (1 s) or long (7 s) delay, and sequences of memory-guided saccades. Compared with controls, patients had normal latency in the gap task but increased latency in the other tasks. The gain of memory-guided saccades was markedly decreased, bilaterally, whatever the duration of the delay. Patients made more errors than controls in the antisaccade task when the 5° lateral target was used, and a higher percentage of chronological errors in the sequences of saccades. These results show that the posterior part of the right ACC plays an important role in eye movement control and suggest that this area could correspond to a “cingulate eye field” (CEF). The role of this hypothetical CEF could be an early activation exerted on the frontal ocular motor areas involved in intentional saccades and also a direct action on brainstem ocular premotor structures.

Notes: Abstract  We investigated the cerebral cortical route by which visual information reaches motor cortex when visual signals are used for manual responses. Subjects responded unimanually to photic stimuli delivered to the hemifield ipsilateral or contralateral to the moving hand. On some trials, trans-cranial magnetic stimulation (TMS) was applied unilaterally over the occiput, with the aim of stimulating extrastriate visual areas and thereby modifying transmission of visual input. In association with the side of a visual stimulus and a motor response, TMS could change inter- or intra-hemispheric transmission needed to convey visual information to motor areas. Reaction time differences following TMS suggested that TMS exerted an inhibitory effect only when visuo-motor information had to be transferred interhemispherically. This result reinforces evidence for an extrastriate pathway of interhemispheric transfer of visuomotor information.

Notes: Abstract  We studied horizontal eye movements evoked by lateral whole body translation in nine patients who underwent vestibular nerve section. Preoperatively, all had preserved caloric function on both sides. Testing was performed before, 1 week and 6–10 weeks after surgery. Patients were seated upright in an electrically powered car running on a linear track. The car executed acceleration steps of 0.24 g, randomly to the left and right in the dark. The normal response consisted of a bidirectionally symmetrical nystagmus with compensatory slow phases. Response asymmetry of the slow-phase velocity of the desaccaded and averaged eye position signal was less than 13% in normals (n = 21). Before surgery, patients’ responses were mostly symmetrical. Postoperatively, responses were diminished or absent with head acceleration towards the operated ear in all patients, causing a marked asymmetry which averaged 56% after correction for spontaneous nystagmus. On follow-up, responses regained symmetry. Thus, early after vestibular nerve section, a single utricle produces a normal LVOR only with ipsilateral head translation. Therefore, afferents for the LVOR seem to originate from the mid-lateral area of the macula, where hair cells are stimulated in their on-direction during ipsilateral head translation. Compensation may depend on recovery of the off-directional responses from lateral hair cells of the remaining utricle.

Notes: Abstract  This study assessed whether stationary auditory information could affect body and head sway (as does visual and haptic information) in sighted and congenitally blind people. Two speakers, one placed adjacent to each ear, significantly stabilized center-of-foot-pressure sway in a tandem Romberg stance, while neither a single speaker in front of subjects nor a head-mounted sonar device reduced center-of-pressure sway. Center-of-pressure sway was reduced to the same level in the two-speaker condition for sighted and blind subjects. Both groups also evidenced reduced head sway in the two-speaker condition, although blind subjects’ head sway was significantly larger than that of sighted subjects. The advantage of the two-speaker condition was probably attributable to the nature of distance compared with directional auditory information. The results rule out a deficit model of spatial hearing in blind people and are consistent with one version of a compensation model. Analysis of maximum cross-correlations between center-of-pressure and head sway, and associated time lags suggest that blind and sighted people may use different sensorimotor strategies to achieve stability.

Notes: Abstract  A single keystroke during touch-typing is a rapid, goal-directed motion of the fingertip which consists of two single-direction movements. The neural control and the role of the finger extrinsic musculature during typing have not yet been explained. The fingertip motion and force, and the intramuscular electromyographic (EMG) activity (fine-wire) of the index finger extrinsic musculature were measured during touch-typing by ten experienced typists. The motions and forces were repeatable qualitatively across keystrokes. A three-burst EMG pattern was observed during a single keystroke. The three bursts were: (1) a burst of extensor activity lifted the finger before the keystroke; (2) a burst of flexor activity followed while the fingertip was moving downward; and (3) a second burst of extensor activity occurred as the fingertip reached the end of key travel. The timing of the third burst suggests the role of the extensors is to remove the fingertip from the keyswitch rather than stop the downward motion of the finger. The collision with the end of key travel stops the downward finger motion. The timing of the finger flexor EMG activity, burst 2, suggests that the flexor contraction principally overcomes the activation force of the keyswitch rather than accelerates the finger downward as expected.

Notes: Abstract  Neural projections from the pronator teres (PT) muscle to biceps brachii (BB) motoneurones were studied in three healthy human subjects using a post-stimulus time histogram method. In 25 BB motor units, electrical stimulation to the PT nerve with intramuscular needle electrodes induced inhibition in nine units (36%), whereas facilitation was produced in 18 units (72%) by stimulation to the median nerve trunk with surface electrodes at the distal end of the intermuscular septum of the arm or in the cubital fossa. Six motor units (24%) received both inhibition (PT nerve stimulation) and facilitation (median nerve trunk stimulation). In the six, the latency of the inhibition was, on average, 1.2 ms longer than that of the facilitation. The stimulation site for the inhibition was, on average, 4.8 cm distal to that for the facilitation. The inhibition was evoked with an intensity well below the motor threshold. These findings suggest that BB motoneurones receive oligosynaptic inhibition of group I afferents from PT in human.

Notes: Abstract  We studied the changes in the anticipatory postural adjustments (APAs), associated with dropping a load from extended arms and during fast bilateral shoulder flexion movements, when movements were performed in a self-paced manner and under a simple reaction-time instruction. The latter instruction applied time pressure and did not allow the regular pattern of APAs to be used. In particular, the following questions were asked: (1) are there changes in the relative timing of APAs under the reaction time condition; (2) are changes in the relative timing of APAs associated with changes in APAs themselves; (3) can different postural strategies be used to maintain stability under self-paced and reaction time conditions; and (4) are changes in APAs related to actual reaction time or to a change in the instruction? In particular, under reaction-time conditions, APAs occurred later in time, typically simultaneously with the initiation of the focal movement. Additional changes in electromyographic (EMG) patterns in postural muscles included an increase in the amplitude of EMG bursts and “speeding-up” some of the tri-phasic patterns in postural dorsal-ventral muscle pairs. This was accompanied by a smaller early shift of the center of pressure followed by its more rapid delayed displacement. There was considerable variability in the changes of EMG and dynamic characteristics across subjects. Some of the changes in the EMG patterns in postural muscles depended on actual reaction time, while others were related to a change in the instruction and occurred even if actual reaction times were long enough to allow for the typical self-paced APA patterns to occur. These findings can be interpreted as supporting the parallel control hypothesis for the focal movement and postural adjustments. Alternatively, they can be interpreted within a framework that implies the generation of a single control function, which is transformed into two components, one directed at the focal muscles/joints and the other directed at postural muscles/joints.

Notes: Abstract  Current models of spatial neglect focus on deficits in the patients’ horizontal or midsagittal plane. However, other evidence suggests that patients with temporoparietal lesions centered on the parieto-insular-vestibular cortex show disturbed spatial perception of the subjective visual vertical and oblique orientation discrimination in another spatial plane, the frontal plane. As the relationship between neglect and spatial orientation deficits is unclear, we examined how patients with and without visual neglect perform visuospatial tasks in the roll plane and how their performance is related to neglect. Thirteen patients with predominantly right parietal lesions and left-sided neglect, 14 control patients without neglect after right-hemispheric cerebral lesions (RBD-controls), 11 patients without neglect after left-hemispheric lesions (LBD-controls), 3 patients with right-sided neglect after left parietal lesions, and 12 normal subjects were investigated. Constant errors and difference thresholds were measured with a PC-based system when the subjects had to adjust a luminous line to their subjective visual vertical, subjective visual horizontal, and in relation to an obliquely oriented reference line. Subjects were oriented with their head and body earth-vertical while sitting in a chair in total darkness. Patients with left-sided as well as those with right-sided neglect showed a significant, in most cases contraversive, tilt of the three spatial orientations (about 5° counterclockwise in the left neglect group and 5.5°–8.5° clockwise in the right neglect group). In contrast, the two patient groups without neglect as well as the normal subjects showed nearly perfect visuospatial judgements with constant errors of less than 0.8°. Difference thresholds were significantly elevated in patients with left neglect and in two of three patients with right-sided neglect, whereas normal control subjects and both control patient groups without neglect performed indistinguishably, having thresholds of one-tenth of those of the neglect patients. Tilt of all three spatial axes was significantly related to the severity of neglect (mean r for unsigned errors, 0.74; for difference thresholds, 0.40), indicating a significant contribution to the symptomatology of left and right spatial neglect. These results indicate a close although not necessarily causal link between spatial orientation deficits in the frontal plane and hemispatial neglect in patients with left or right parietal lesions, surpassing the well-documented impairments of these patients in the horizontal plane.

Notes: Abstract  Based on previous studies, we formulated a principle of error compensation as a major principle of synergy organization during motor tasks performed by a redundant set of effectors. Within the present study, we tested the principle by an investigation of the performance of individual fingers during isometric force production when another task was performed simultaneously. Subjects were asked to press at about 30% of the maximal contraction force with three fingers (index, middle, and ring) acting in parallel. Then, they were required to perform a series of taps at 2 Hz with one of the fingers. In all the tasks, nontapping fingers changed their force production without a time delay with the changes in the force by the tapping finger. During tapping with the index and with the middle finger, both nontapping fingers showed changes in their force negatively correlated with changes in force of the tapping finger. During tapping with the ring finger, two types of behavior could be seen in different subjects with the force of the middle finger going out of phase (group 1) or in phase (group 2) with the force of the ring finger. In both cases, the force of the index finger was out of phase with the force of the ring finger. These changes, on average, induced a compensation for the expected drop in finger force during tapping, ranging in different conditions from 94% to 102%. The ratio of forces produced by the nontapping fingers did not change during the tapping in all the cases except group 2 during ring-finger tapping, when the index finger started to generate significantly higher force as compared to the middle finger. We interpret the data as results of the action of a feed-forward central mechanism leading to parallel changes in forces produced by fingers united into a structural unit.

Notes: Abstract  The purpose of this study was to determine the precision of proprioceptive localization of the hand in humans. We derived spatial probability distributions which describe the precision of localization on the basis of three different sources of information: proprioceptive information about the left hand, proprioceptive information about the right hand, and visual information. In the experiment subjects were seated at a table and had to perform three different position-matching tasks. In each task, the position of a target and the position of an indicator were available in a different combination of two of these three sources of information. From the spatial distributions of indicated positions in these three conditions, we derived spatial probability distributions for proprioceptive localization of the two hands and for visual localization. For proprioception we found that localization in the radial direction with respect to the shoulder is more precise than localization in the azimuthal direction. The distributions for proprioceptive localization also suggest that hand positions closer to the shoulder are localized more precisely than positions further away. These patterns can be understood from the geometry of the arm. In addition, the variability in the indicated positions suggests that the shoulder and elbow angles are known to the central nervous system with a precision of 0.6–1.1°. This is a considerably better precision than the values reported in studies on perception of these angles. This implies that joint angles, or quantities equivalent to them, are represented in the central nervous system more precisely than they are consciously perceived. For visual localization we found that localization in the azimuthal direction with respect to the cyclopean eye is more precise than localization in the radial direction. The precision of the perception of visual direction is of the order of 0.2–0.6°.

Notes: Abstract  Patients with bilateral vestibular loss have difficulty maintaining balance without stepping when standing in tandem, on compliant surfaces, across narrow beams, or on one foot, especially with eyes closed. Normal individuals (with no sensory impairment) maintain balance in these tasks by employing quick, active hip rotation (a “hip strategy”). The absence of a hip strategy in vestibular patients responding to translations of a short support surface has previously been taken as evidence that the use of hip strategy requires an intact vestibular system. However, many tasks requiring hip strategy alter one or a combination of important system characteristics, such as initial state of the body (tandem stance), dynamics (compliant surfaces), or biomechanical limits of stability (narrow beams). Therefore, the balance deficit in these tasks may result from a failure to account for these support surface alterations when planning and executing sensorimotor responses. In this study, we tested the hypothesis that vestibular information is critical to trigger a hip strategy even on an unaltered support surface, which imposes no changes on the system characteristics. We recorded the postural responses of vestibular patients and control subjects with eyes closed to rearward support surface translations of varying velocity, in erect stance on a firm, flat surface. Subjects were instructed to maintain balance without stepping, if possible. Faster translation velocities (25 cm/s or more) produced a consistent pattern of early hip torque (first 400 ms) in control subjects (i.e., a hip strategy). Most of the patients with bilateral vestibular loss responded to the same translation velocities with similar torques. Contrary to our hypothesis, we conclude that vestibular function is not necessary to trigger a hip strategy. We postulate, therefore, that the balance deficit previously observed in vestibular patients during postural tasks that elicit a hip strategy may have been due to the sensorimotor consequences of the system alterations imposed by the postural tasks used in those studies. Preliminary results from two younger patients who lost vestibular function as infants indicate that age, duration of vestibular loss, and/or the timing of the loss may also be factors that can influence the use of hip strategy as a rapid postural response.

Notes: Abstract  Colour matching and colour constancy were studied in seven patients and 46 control subjects. Subjects were required to match Munsell Colour Chips presented under either identical or different illumination. Three of the patients had deficits in colour constancy, i.e. failure to compensate for the change in the wavelength composition of the illumination. Two of the patients with defective constancy had suffered bilateral cortical damage to the poterior lingual and fusiform gyri, and one patient had a lesion restricted to the same regions of the right hemisphere. Our observations indicate that these cortical areas, which include part of putative human area V4, play an important role in colour constancy.

Notes: Abstract  Saccadic eye movements are controlled by a cortical network composed of several oculomotor areas that are now accurately localized. Clinical and experimental studies have enabled us to understand their specific roles better. These areas are: (1) the parietal eye field (PEF) located in the intraparietal sulcus involved in visuospatial integration and in reflexive saccade triggering; (2) the frontal eye field (FEF), located in the precentral gyrus, involved in the preparation and the triggering of purposive saccades; and (3) the supplementary eye field (SEF) on the medial wall of the frontal lobe, probably involved in the temporal control of sequences of visually guided saccades and in eye-hand coordination. A putative cingulate eye field (CEF), located in the anterior cingulate cortex, would be involved in motivational modulation of voluntary saccades. Besides these motor areas, the dorsolateral prefrontal cortex (dlPFC) in the midfrontal gyrus is involved in reflexive saccade inhibition and visual shortterm memory.

Notes: Abstract  It is still not clear whether the transition from pursuit eye movements to fixation is mediated by the same system that initiates pursuit, or whether another system, a specialized fixation system, is responsible. To investigate this question we measured smooth-pursuit eye movements and smooth-pursuit termination in five normal subjects using both predictable and unpredictable step-ramp stimuli (velocities 10° and 20°/s) in front of a homogeneous and a structured visual background in order to compare the profile of eye velocity under these different conditions. With the predictable and/or structured visual background there was a gradual transition of eye velocity toward zero. In contrast, with the unpredictable stimulus in front of a homogeneous background, eye velocity during the offset was characterized by an overshoot (on the average, 2.2±1.0°/s for 10°/s ramps) before eye velocity settled at zero. Under this condition, steady-state velocity gain and the deceleration of the offset were significantly higher than during the other paradigm with the same target velocity. The latency of the pursuit offset was significantly shorter when a predictable stimulus was used. The duration of the offset did not depend on the experimental condition used. These findings imply that the pursuit onset and offset have some similarities and may be mediated by the same oculomotor system.

Notes: Abstract  Recent research suggests that the balance requirements of a task dictate the reflexive response. However, these observations were inferred indirectly from either different tasks or different phases of the same task. This study directly tested the hypothesis of balance-dependent control during recovery from an unexpected trip. The subjects were tripped in two different support conditions: unilimb support (provided by the stance limb) or trilimb support (provided by the stance limb and both arms placed on adjacent parallel bars). The subjects exhibited anticipatory changes: they biased the body center of mass toward the support limb in the mediolateral direction and elevated the swing limb higher when there was a possibility of being tripped. The electromyographic (EMG) latencies were not influenced by the threat to equilibrium. The magnitudes of the EMG reflexive response to the trip were clearly modulated as a function of the threat to stability, not in a simple manner, but rather in a complex manner, which optimized the recovery strategy. It is evident that the overriding concern, equilibrium control during locomotion, has a dominant influence on reflex modulation.

Notes: Abstract  A magnetic transcranial conditioning stimulus given over the motor cortex at intensities below threshold for obtaining electromyographical (EMG) responses in active hand muscles can suppress responses evoked in the same muscles at rest by a suprathreshold magnetic test stimulus given 1–5 ms later. In order to define the mechanism of this inhibitory effect, we recorded descending volleys produced by single and paired magnetic transcranial stimulation of motor cortex through high cervical, epidural electrodes implanted for pain relief in two conscious subjects with no abnormality of the central nervous system. The conditioning stimulus evoked no recognisable descending activity in the spinal cord, whilst the test stimulus evoked 3–4 waves of activity (I-waves). Conditioning stimulation suppressed the size of both the descending spinal cord volleys and the EMG responses evoked by the test stimulus. Inhibition of the descending spinal volleys was most pronounced at ISI 1 ms and had disappeared by ISI 5 ms. It was evident for all components following the I1-wave, while the I1-wave itself was not inhibited at all. We conclude that a small conditioning magnetic stimulus can suppress the excitability of human motor cortex, probably by activating local cortico-cortical inhibitory circuits.

Notes: Abstract  The aim of this study was to test Bernstein’s idea that motor synergies provide solutions to the motor redundancy problem. Forces produced by individual fingers of one hand were recorded in one-, two-, three-, and four-finger tasks. The subjects (n=10) were asked to produce maximal total force (maximal voluntary contraction, MVC) and to match a ramp total force profile using different combinations of fingers. We found that individual finger forces were smaller in multifinger MVC tasks than in single-finger tasks. The deficit increased with the number of fingers involved. A saturation effect was observed: when several effectors were involved, adding a new effector did not significantly change the total force output. The data confirmed the idea that the central neural drive arriving at the level of synergies has a certain limit, a ceiling, that cannot be exceeded. The central nervous system cannot maximally activate the muscles serving all the fingers at the same time. Secondly, during the course of ramp trials, forces produced by individual fingers were linearly related to each other. Hence, a force sharing pattern was established at the beginning of the trial and did not change during the ramp period. A hypothesis is suggested that force distribution among fingers may be organized so as to minimize unnecessary rotational moment with respect to the functional longitudinal axis of the hand. Finally, in the four-finger trials, variance of the total maximal force output in ten consecutive attempts was smaller than the sum of variances of the maximal individual finger forces. The finding suggests that the control system of the motor tasks studied involves at least two levels, a central neural drive level and a synergy level. At the synergy level, an intercompensation in individual finger force production is observed.

Notes: Abstract  Head tilt is a rotation of the head relative to gravity, as exemplified by head roll or pitch from the natural upright orientation. Tilt stimulates both the otolith organs, owing to shifts in gravitational orientation, and the semicircular canals in response to head rotation, which in turn drive a variety of behavioral and perceptual responses. Studies of tilt perception typically have not adequately isolated otolith and canal inputs or their dynamic contributions. True tilt cannot readily dissociate otolith from canal influences. Alternatively, centrifugation generates centripetal accelerations that simulate tilt, but still entails a rotatory (canal) stimulus during important periods of the stimulus profiles. We reevaluated the perception of head tilt in humans, but limited the stimulus to linear forces alone, thus isolating the influence of otolith inputs. This was accomplished by employing a centrifugation technique with a variable-radius spinning sled. This allowed us to accelerate the sled to a constant angular velocity (128°/s), with the subject centered, and then apply dynamic centripetal accelerations after all rotatory perceptions were extinguished. These stimuli were presented in the subjects’ naso-occipital axis by translating the subjects 50 cm eccentrically either forward or backward. Centripetal accelerations were thus induced (0.25 g), which combined with gravity to yield a dynamically shifting gravitoinertial force simulating pitch-tilt, but without actually rotating the head. A magnitude-estimation task was employed to characterize the dynamic perception of pitch-tilt. Tilt perception responded sluggishly to linear acceleration, typically reaching a peak after 10–30 s. Tilt perception also displayed an adaptation phenomenon. Adaptation was manifested as a per-stimulus decline in perceived tilt during prolonged stimulation and a reversal aftereffect upon return to zero acceleration (i.e., recentering the subject). We conclude that otolith inputs can produce tilt perception in the absence of canal stimulation, and that this perception is subject to an adaptation phenomenon and low-pass filtering of its otolith input.

Notes: Abstract  We sought to determine whether an increase in judged egocentric distance created by increasing vergence-specified distance would be negated when participants pointed at their own finger. It was found that ocular position dominates limb proprioception in the judgement of finger distance in the sagittal plane when vision is available. In contrast, an increase in perceived egocentric distance was largely attenuated by the presence of limb proprioception in reduced visual cue conditions. We conclude that the relative contribution of vergence to perceived distance depends upon the strength of the vergence effort signal when there are other cues present. Furthermore, if the distance percept includes a major contribution from retinal cues, then the visual component will dominate the limb proprioception component. If the visual component is largely determined by vergence information, limb proprioception will make a significant contribution and actually dominate when the vergence effort signal is weak. The results extend previous studies that have found a similar relationship between ocular position and limb proprioception in the perception of a finger′s location in the coronal plane.

Notes: Abstract  In 12 subjects, each sitting on an armchair with the right forearm prone, the H-reflex elicited in the resting flexor carpi radialis muscle underwent cyclic excitability changes correlated with rhythmic flexion-extension movements of the ipsilateral foot (frequency of oscillations between 1.5 and 2.5 Hz). During foot plantar flexion, the H-reflex underwent a clear-cut increase, the maximum facilitation falling, in most subjects, within the second half of that phase; then, a gradual reduction in size led the reflex amplitude back to the initial value at the end of foot dorsal extension. If present also when the wrist and the ankle are moved together, this facilitation should favour the in-phase (isodirectional) association between movements and, conversely, hinder the anti-phase coupling.

Notes: Abstract  We have studied the effects of pursuit eye movements on the functional magnetic resonance imaging (fMRI) responses in extrastriate visual areas during visual motion perception. Echoplanar imaging of 10–12 image planes through visual cortex was acquired in nine subjects while they viewed sequences of random-dot motion. Images obtained during stimulation periods were compared with baseline images, where subjects viewed a blank field. In a subsidiary experiment, responses to moving dots, viewed under conditions of fixation or pursuit, were compared with those evoked by static dots. Eye movements were recorded with MR-compatible electro-oculographic (EOG) electrodes. Our findings show an enhanced level of activation (as indexed by blood-oxygen level-dependent contrast) during pursuit compared with fixation in two extrastriate areas. The results support earlier findings on a motion-specific area in lateral occipitotemporal cortex (human V5). They also point to a further site of activation in a region approximately 12 mm dorsal of V5. The fMRI response in V5 during pursuit is significantly enhanced. This increased response may represent additional processing demands required for the control of eye movements.

Notes: Abstract  The purpose of the present experiment was to study the way in which the central nervous system (CNS) represents gravitational force (GF) during vertical drawing movements of the arm. Movements in four different directions: (a) upward vertical (0°), (b) upward oblique (45°), (c) downward vertical (180°) and (d) downward oblique (135°), and at two different speeds, normal and fast, were executed by nine subjects. Data analysis focused upon arm movement kinematics in the frontal plane and gravitational torques (GTs) exerted around the shoulder joint. Regardless of movement direction, subjects showed straight-line paths for both speed conditions. In addition, movement time and peak velocity were not affected by movement direction and consequently changes in GT, for both speeds tested. Movement timing (evaluated through the ratio of acceleration time to total time) changed significantly, however, as a function of movement direction and speed. Upward movements showed shorter acceleration times when compared with downward movements. Concerning the four directions, movements made at 0° and 45° differed significantly from those made at 135° and 180°. Drawing movements executed at rapid speed presented similar acceleration and deceleration times compared with movements executed at normal speed, which showed greater acceleration than deceleration times. In addition, the form of velocity profiles (assessed through the ratio of maximum to mean velocities), was significantly modified only with movement speed. Results from the present study suggest that GF is efficiently incorporated into internal dynamic models that the brain builds up for the execution of arm movements. Furthermore, it seems that GF not only is a mechanical parameter to be overcome by the motor system but also constitutes a reference (vertical direction), both of which are represented by the CNS during inverse kinematic and dynamic processes.

Notes: Abstract  In two previous studies, the readiness potential (RP) has been reported to be influenced by the mode of movement selection. Freely selected movements were found to have a higher RP amplitude than fixed repetitive movements. This was attributed to the higher demands on planning for the performance of freely selected movements. However, movements in the free mode are distinct from movements in the fixed mode in more than one respect. For example, they are also associated with a higher degree of alteration of the side and/or the finger of movement execution and hence serial “novelty” across blocks of trials. The aim of our study was to establish whether the greater novelty of movements in the free mode could also contribute to the enhanced RP amplitude of movements in the free mode of movement selection by comparing free versus fixed movements performed in long and short sequences that differ in terms of serial novelty. The RP was recorded in 31 healthy young subjects with electrodes placed over Fz, C3, Cz, C4 and Pz. Two types of movement were studied: randomly chosen button presses with right or left index or middle finger (free mode), and repetitive pressing of a predetermined button (fixed mode). We found that: (1) in confirmation of previous studies, the amplitude of the RP was higher for freely selected than free movements; (2) the effect of the mode of movement selection was present over central electrodes but was most pronounced for parietal electrode Pz, with movements in the free mode showing the earliest and greatest increase in negativity at this site; (3) this parietally enhanced negativity in free compared with the fixed mode was absent after the subjects had performed a block of long movement sequences, suggesting that serial novelty of movements also contributed to the effect of mode on the RP amplitude; (4) both the latency and the magnitude of the lateralized readiness potential (LRP) were altered by the mode of movement selection. Movements in the free mode showed an earlier onset of the LRP, which had a higher peak than the LRP prior to movements in the fixed mode. This effect was mainly due to an increased amplitude of the RP over the electrode contralateral to the side of movement prior to freely selected movements. These findings are discussed in relation to previous RP and positron emission tomography studies.

Notes: Abstract  A reduced gain of smooth pursuit eye velocity has frequently been reported in schizophrenic patients. With respect to predictable stimuli, this could be due to a deficit in predicting the target path. To determine this contribution to smooth pursuit eye movement performance, we analyzed the ocular smooth pursuit response to a sinusoidally moving target that was suddenly stopped after some cycles of regular movement. Horizontal eye movements were recorded with infrared reflection oculography in a group of 17 schizophrenic in-patients and 16 age-matched healthy subjects for controls. The patients exhibited a reduced gain of smooth pursuit velocity, but phase lag was not different from the control group. After the unpredictable stop of target movement, predictive sinusoidal smooth pursuit was maintained for 150 to 200 ms in both groups. The resulting maximal position and velocity error was larger in the patient group. In conclusion, schizophrenic patients were able to generate a normal anticipatory component of smooth pursuit and to switch it off in response to external demands. They showed, however, an increased velocity of anticipatory pursuit, which might be used to compensate for the primary deficit of smooth pursuit velocity frequently found in schizophrenics.

Notes: Abstract  The present study characterizes a previously reported adaptive phenomenon in a somatosensory-motor system involved in directional control of locomotor trajectory through foot contact with the floor. We call this the “podokinetic” (PK) system. Podokinetic adaptation was induced in six subjects by stepping in-place over the axis of a horizontally rotating disc over a range of disc angular velocities (11.25–90°/s) and durations (7.5–60 min). After adaptation, subjects were blindfolded and attempted to step in-place on the floor without turning. Instead they all rotated relative to space. The rate of the “podokinetic afterrotation” (PKAR) was linearly related to stimulus amplitude up to 45°/s, and the ratio of initial PKAR velocity to that of the adaptive stimulus was approximately 1:3. PKAR exhibited exponential decay, which was composed of “short-” and “long-term” components with “discharging” time constants on the order of 6–12 min and 1–2 h, respectively. The effect of stimulus duration on PKAR revealed a “charging” time constant that approximated that of the short-term component. A significant suppression of PKAR occurred during the 1st min of the postadaptive response, suggesting functional interaction between the PK and vestibular systems during the period of vestibular stimulation. During PKAR subjects perceived no self-rotation, indicating that perception as well as locomotor control of spatial orientation were remodeled by adaptation of the PK system.

Notes: Abstract  We used positron emission tomography (PET) to measure movement set-related changes in regional cerebral blood flow (rCBF) when human subjects were asked to copy hand movements. Movement set-related activity in the brain is thought to reflect the processes of movement selection, preparation and inhibition. Four conditions were used. In the first condition, prepare and execute (PE), the hand stimulus to be copied was shown to subjects 3 s before an auditory “go”-cue instructed subjects to execute the movement; a large part of the scanning time was therefore spent in preparing to move. In the immediate execution condition (E), the hand stimulus and the go cue were presented simultaneously. The prepare-only condition (P) was similar to PE, except subjects only prepared to make the movement and did not actually execute any movement when they heard the auditory go-cue. The same stimuli were presented in a baseline condition (B), but the subjects were instructed to neither prepare nor execute movements. There were 5 principle findings: (1) In contrast to a previous study of human set-related activity in which movements were instructed by an arbitrary pattern of LEDs, preparing to make a copied movement causes rCBF changes in area 44 in posterior Broca’s area; (2) set-related activity can be recorded in the cerebellar hemispheres and midline; (3) we confirmed that the supramarginal gyrus has a general role in preparing movements – there was more rCBF in the P than the E condition; (4) the cerebellar nuclei and the basal ganglia may be particularly involved in the initiation and execution of a planned movement; these regions were more active in the PE condition than the P condition; (5) the ventrolateral prefrontal cortex and a left anterior cingulate area are part of a distributed system involved in the suppression of a motor response; these areas were significantly more active in the P than the PE condition.

Notes: Abstract  The reaction times of saccades (SRT) to a suddenly presented visual stimulus (pro-saccade) can be decreased and a separate mode of express saccades can occur when a gap paradigm is used (i.e. fixation-point offset precedes target onset by 200 ms). A valid peripheral cue, presented briefly (100 ms) before target onset, has been found to facilitate the generation of saccades to the target, thereby increasing the frequency of express saccades and decreasing the mean latency. This facilitation occurs only for cues that correctly indicate the direction of the subsequent target presentation (valid cues). The present study investigates the effects of valid cues on SRTs and error rate in the anti-saccade task (saccades in the direction opposite to the stimulus) by systematically varying the cue lead time (CLT) and using the gap and overlap conditions, i.e. fixation point remains on throughout the trial. For a CLT of 100 ms, both reaction times and error rates were significantly increased. With increasing CLT (200–500 ms), both the reaction times of the anti-saccades and the error rates returned to approximately control level, with CLT more than 200 ms in both the gap and the overlap condition. Additional experiments using non-informative cues in the overlap task showed that the reaction times of correct anti-saccades and the error rate were decreased when cue and stimulus appeared at the same side. Analysis of the erratic pro-saccades revealed that almost all of them were corrected, i.e. they were followed by a second saccade towards the required location. It is found that the correction times were usually very short, with intersaccadic intervals between 0 and 150 ms. We suggest that the orienting mechanism, elicited by a transient peripheral cue, relates to the command and the decision to make a pro- rather than an anti-saccade. The cue elicits pro-orienting towards its position when a pro-saccade is required, and anti-orienting when an anti-saccade is required. The orienting effect is transient and decays with CLTs of more than 200 ms; this result holds for both anti-saccades and pro-saccades. Since subjects reported that they could not prevent the erratic pro-saccades or were often not aware of them, we conclude that this orienting mechanism occurs automatically, beyond voluntary control.

Notes: Abstract  Proprioceptive input arising from torsional body movements elicits small reflexive eye movements. The functional relevance of these eye movements is still unknown so far. We evaluated their slow components as a function of stimulus frequency and velocity. The horizontal eye movements of seven adult subjects were recorded using an infrared device, while horizontal rotations were applied at three segmental levels of the body [i.e., between head and shoulders (neck stimulus), shoulders and pelvis (trunk stimulus), and pelvis and feet (leg stimulus)]. The following results were obtained: (1) Sinusoidal leg stimulation evoked an eye response with the slow component in the direction of the movement of the feet, while the response to trunk and neck stimulation was oriented in the opposite direction (i.e., in that of the head). (2) In contrast, the gain behavior of all three responses was similar, with very low gain at mid- to high frequencies (tested up to 0.4 Hz) but increasing gain at low frequencies (down to 0.0125 Hz). We show that this gain behavior is mainly due to a gain nonlinearity for low angular velocities. (3) The responses were compatible with linear summation when an interaction series was tested in which the leg stimulus was combined with a vestibular stimulus. (4) There was good correspondence of the median gain curves when eye responses were compared with psychophysical responses (perceived body rotation in space; additionally recorded in the interaction series). However, correlation of gain values on a single-trial basis was poor. (5) During transient neck stimulation (smoothed position ramp), the neck response noticeably consisted of two components – an initial head-directed eye shift (phasic component) followed by a shift in the opposite direction (compensatory tonic component). Both leg and neck responses can be described by one simple, dynamic model. In the model the proprioceptive input is fed into the gaze network via two pathways which differ in their dynamics and directional sign. The model simulates either leg or neck responses by selecting an appropriate weight for the gain of one of the pathways (phasic component). The interaction results can also be simulated when a vestibular path is added. This model has similarities to one we recently proposed for human self-motion perception and postural control. A major difference, though, is that the proprioceptive input to the gaze-stabilizing network is weak (restricted to low velocities), unlike that used for perception and postural control. We hold that the former undergoes involution during ontogenesis, as subjects depend on the functionally more appropriate vestibulo-ocular reflex. Yet, the weak proprioceptive eye responses that remain may have some functional relevance. Their tonic component tends to stabilize the eyes by slowly shifting them toward the primary head position relative to the body support. This applies solely to the earth-horizontal plane in which the vestibular signal has no static sensitivity.

Notes: Abstract  It has been hypothesized previously that because a strong correlation was found between the difference in electromyographic activity (EMG) of rectus femoris (RF) and hamstrings (HA; EMGRF–EMGHA) and the difference in the resultant moments at the knee and hip (Mk–Mh) during exertion of external forces on the ground by the leg, input from skin receptors of the foot may play an important role in the control of the distribution of the resultant moments between the knee and hip by modulating activation of the two-joint RF and HA. In the present study, we examined the coordination of RF and HA during the swing phase of walking and running at different speeds, where activity of foot mechanoreceptors is not modulated by an external force. Four subjects walked at speeds of 1.8 m/s and 2.7 m/s and ran at speeds of 2.7 m/s and 3.6 m/s on a motor-driven treadmill. Surface EMG of RF, semimembranosus (SM), and long head of biceps femoris (BF) and coordinates of the four leg joints were recorded. An inverse dynamics analysis was used to calculate the resultant moments at the ankle, knee, and hip during the swing phase. EMG signals were rectified and low-pass filtered to obtain linear envelopes and then shifted in time to account for electromechanical delay between EMG and joint moments. During walking and running at all studied speeds, mean EMG envelope values of RF were statistically (P〈0.05) higher in the first half of the swing (or at hip flexion/knee extension combinations of joint moments) than in the second half (or at hip extension/knee flexion combinations of joint moments). Mean EMG values of BF and SM were higher (P〈0.05) in the second half of the swing than in the first half. EMG and joint moment peaks were substantially higher (P〈0.05) in the swing phase of walking at 2.7 m/s than during the swing phase of running at the same speed. Correlation coefficients calculated between the differences (EMGRF–EMGHA) and (Mk–Mh), taken every 1% of the swing phase, were higher than 0.90 for all speeds of walking and running. Since the close relationship between EMG and joint moments was obtained in the absence of an external force applied to the foot, it was suggested that the observed coordination of RF and HA can be regulated without a stance-specific modulation of cutaneous afferent input from the foot. The functional role of the observed coordination of RF and HA was suggested to reduce muscle fatigue.

Notes: Abstract  The purpose of the present experiment was to study the way in which the central nervous system (CNS), represents gravitational force during vertical arm pointing movements. Movements in upward (against gravity) and downward (with gravity) directions, with two different mass loads (hand empty and with a hand-held 0.5-kg weight) were executed by eight subjects in a normal gravitational environment. Movements by two cosmonauts, in the two directions, were also tested in a state of weightlessness. Analyses focused upon finger trajectories in the saggital plane. Subjects in a normal gravitational environment showed curved paths for both directions and weight conditions. In addition, downward movements showed significantly smaller curvatures than upward movements. Movement times were approximately the same for all the experimental conditions. Curvature differences between upward and downward movements persisted during space flight and immediately postflight. Movement times from both cosmonauts increased slightly during flight, but returned to normal immediately on reentry in a one-G environment. Results from the present study provide evidence that gravity is centrally represented in an anticipatory fashion as a driving force during vertical arm movement planning.