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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular medicine 65 (1987), S. 542-545 
    ISSN: 1432-1440
    Keywords: Transcranial Doppler ; Intracranial pressure ; Cerebral diseases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the course of a pilot study, changes in intracranial pressure were compared with the transcranial Doppler findings of the middle cerebral artery. The cases of five patients were discussed who developed dissociated brain death in spite of intensive therapeutic measures. The studies showed that changes of the intracranial pressure influenced the flow patterns considerably: at increasing intracranial pressure (decreasing cerebral perfusion pressure) a progressive reduction of the systolic and above all diastolic flow velocities and finally a pendular flow occurred. These changes could be recorded quantitatively by means of the “Pourcelot index” and the mean flow velocity. Acute changes of the intracranial pressure can be detected at an early stage by noninvasive transcranial Doppler studies and can be followed by adequate intensive therapy.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1459
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1106
    Keywords: Key words Somatotopy ; Input-Output ; Inhibition ; Excitation ; Transcranial magnetic stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Integration of tactile afferent signals with motor commands is crucial for the performance of purposeful movements such as during manipulation of an object in the hand. To study the somatotopic organization of sensorimotor integration we applied electrical peripheral conditioning stimuli to a digit located near (homotopic stimulation) or distant from (heterotopic stimulation) relaxed or isometrically contracted intrinsic hand muscles at variable time intervals prior to transcranial magnetic stimulation (TMS). Cutaneous stimulation has previously been shown to modulate the amplitude of the motor evoked potential (MEP) and to shorten the duration of the silent period (SP) evoked by TMS. In relaxed target muscles the time-dependent modulation of TMS-evoked motor responses by homotopic conditioning stimulation differed from modulation by heterotopic stimulation. Similar differences in the modulation pattern evoked by homotopic and heterotopic conditioning stimulation were observed for two distinct target muscles of the hand (abductor digiti minimi, abductor pollicis brevis muscle). Differences in modulation were maximal when the conditioning stimulation was applied 25–30 ms and 150–200 ms prior to TMS. Comparison of the modulation of the amplitudes of MEPs evoked by transcranial electrical stimulation (TES) and the modulation of those evoked by TMS suggests that differences between homotopic and heterotopic stimulation originate subcortically at 25- to 30-ms and, at least partially, cortically at 150- to 200-ms interstimulus intervals. In isometrically contracted intrinsic hand muscles the degree to which the SP was shortened reflected the location and the timing of the conditioning stimulus. Shortening was maximal when the conditioning stimulus was applied nearest to the contracted target muscle and 20 ms prior to the test stimulus. In contrast to the SP duration, the MEP size in voluntarily contracted target muscles was unaffected by the location of the conditioning stimulus. The somatotopic gradient of SP shortening was abolished when the two target muscles were simultaneously activated isometrically. Together, our findings suggest that somatotopy of input-output relationships is implemented at both a spinal and a cortical level in the human central nervous system and may also depend on the motor task involved.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 21 (1974), S. 113-124 
    ISSN: 1432-1106
    Keywords: Decerebrate rigidity ; Renshaw cell activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of pre- and/or intercollicular decerebration on the activity and responsiveness of individual Renshaw cells were studied in 15 adult cats under continuous light anesthesia. It was found that decerebration either had no effect on the spontaneous activity of Renshaw cells and their response to antidromic stimulation, or it enhanced activity, provided that the blood pressure was prevented from falling below critical values. Spontaneous activity showed the more pronounced increase, particularly after intercollicular decerebration. Severing of the ipsilateral dorsal roots had no noticeable effect on the Renshaw cell behaviour. Concomitant with the release of extensor a-motoneurones following decerebration — as indicated by an augmentation in the amplitude of monosynaptic reflexes — the Renshaw cell response to orthodromic stimulation was enhanced. The phasic response of Renshaw cells, elicited by muscular ramp stretch, was also more pronounced after decerebration. Thus judging by the experimental results obtained in anesthetized animals, any decrease in Renshaw cell activity would not seem to be a primary cause of decerebrate rigidity.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 55 (1984), S. 127-133 
    ISSN: 1432-1106
    Keywords: Ballistic movement ; Three-burst pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In isotonic and isometric goal-directed index finger movements made as fast as possible, the “braking hypothesis” ascribed to the antagonist burst was tested. Under isotonic conditions, the extensor burst often failed to occur in small angle movements with low inertial load. It regularly occurred, however, in small angle movements with high inertial load and in wide angle movements with both low and high inertial loads. Such features suggest, indeed, the antagonist burst as being part of braking strategies. Under isometric conditions, the antagonist burst — if it occurred — exhibited characteristics which suggested a rapidly alternating movement rather than a braking strategy.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 124 (1999), S. 321-330 
    ISSN: 1432-1106
    Keywords: Key words Motor-evoked potentials ; Cortex ; Sensorimotor interaction ; Motor control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In 11 healthy subjects motor-evoked potentials (MEPs) and silent periods (SPs) were measured in the right first dorsal interosseus (FDI) and abductor pollicis brevis muscles (APB): (1) when transcranial magnetic cortex stimulation (TMS) was applied at tonic isometric contraction of 20% of maximum force, (2) when TMS was applied during tactile exploration of a small object in the hand, (3) when TMS was applied during visually guided goal-directed isometric ramp and hold finger flexion movements, and (4) when at tonic isometric contraction peripheral electrical stimulation (PES) of the median nerve was delivered at various intervals between PES and TMS. Of the natural motor tasks, duration of SPs of small hand muscles was longest during tactile exploration (APB 205±42 ms; FDI 213±47 ms). SP duration at tonic isometric contraction amounted to 172±35 ms in APB and 178±31 ms in FDI, respectively. SP duration in FDI was shortest when elicited during visually guided isometric finger movements (159±15 ms). At tonic isometric contraction, SP was shortened when PES was applied at latencies –30 to +70 ms in conjunction with TMS. The latter effect was most pronounced when PES was applied 20 ms before TMS. PES-induced effects increased with increasing stimulation strength up to a saturation level which appeared at the transition to painful stimulation strengths. Both isolated stimulation of muscle afferents and of low-threshold cutaneous afferents shortened SP duration. However, PES of the contralateral median nerve had no effect on SPs. Amplitudes of MEPs did not change significantly in any condition. Inhibitory control of motor output circuitries seems to be distinctly modulated by peripheral somatosensory and visual afferent information. We conclude that somatosensory information has privileged access to inhibitory interneuronal circuits within the primary motor cortex.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 59 (1985), S. 470-477 
    ISSN: 1432-1106
    Keywords: Three-burst pattern ; Rapid goal-directed movements ; Speed control ; Braking process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In rapid goal-directed elbow flexion movements the influence of both movement amplitude and inertial load on the three-burst pattern and the consequences on movement time were studied. Subjects performed visually guided, self-paced movements as rapidly and as accurately as possible. An increase of both the movement amplitude and the inertial load were found to be interacting factors for the modulation of the three-burst-pattern and movement time. The first biceps burst progressively increased in duration and amplitude for larger movements, resulting in prolonged movement times. Surplus inertial loads further prolonged the agonist burst for large, but not for small movement amplitudes. The activity of the antagonist burst, in contrast, was largest in small movements and successively decreased at increasing movement amplitudes. Its duration, however, remained fairly constant. As was similarly observed for the agonist burst, surplus inertial loads lead to a prolongation of antagonist burst duration and an increase of the activity integral for large, but not for small movement amplitudes. It is suggested that in elbow flexion movements the programming of fastest goal-directed movements must take into account neural constraints and biomechanical characteristics of the agonist muscle and the antagonist muscle. Due to neural constraints of the biceps muscle, in contrast to finger movements, the concept of movement time invariance does not hold for elbow movements. Furthermore, neural constraints of the antagonist muscle lead to a limited force production of the agonist muscle at small movement amplitudes in order to avoid an overload of the braking process. The complexity of the relationship between neural and mechanical factors indicate that the size and timing of the three-burst-pattern has to be subtly adjusted to the precise nature of the task and its biomechanical characteristics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 63 (1986), S. 585-595 
    ISSN: 1432-1106
    Keywords: Movement ; Sequence ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The present study analyses the strategies adopted by normal subjects when they are asked to make two separate movements as rapidly as possible one after the other. Five subjects performed the following sequential movements in their own time. 1) Squeeze an isometric force transducer between fingers and thumb to a force of 30 N and then flex the elbow of the same arm through 15°. 2) Squeeze the transducer with one hand and then flex the elbow of the other arm. 3) Perform an isotonic opposition of finger and thumb and then flex the elbow of the same arm. 4) First flex the elbow through 15, 30 or 45° and then squeeze the transducer. 5) Flex and then extend the elbow as rapidly as possible. In tasks 1–4 there was no correlation between the times taken to complete the two separate components of the sequence. Because of this we suggest that the two movements remained under the control of two separate motor programmes. In contrast, in task 5, the times taken for the two components were correlated and hence we suggest that in this case a single programme was used to perform the sequence. In tasks 1–3, in which the mean duration of the first movement was some 135–162 ms, there was a mean pause of about 85 ms before the start of the second movement. Subjects tended to chose a minimum inter-onset latency between the start of the first and the start of the second movement of a sequence of some 230 ms. The reason for this appeared to be that if subjects were encouraged to decrease their interonset latencies to less than 200 ms, the speed of the second movement decreased sharply. However, if the duration of the first movement was prolonged as in task 4, the second movement could be delayed, although there now was little or no pause between the two movements. We conclude that when a single motor programme is run, it is followed by a “relative refractory period”. If a second programme is run within this period, it cannot be executed without loss of speed. Switching from one motor programme to another is achieved with an optimal minimum delay of 200 ms. Sequential movements which are controlled by a single programme do not share this limitation.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 21 (1974), S. 353-360 
    ISSN: 1432-1106
    Keywords: Renshaw cells ; Muscle stretch ; Phasic tonic motoneurones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary a) Renshaw cells (RC) were recorded during ramp stretch of the GS muscle. In 90% of the analysed cells, the frequency and duration of the phasic response were enhanced by increases in both the length and rate of stretch. b) The tonic response, which was observed in about 30% of the analysed cells, increased at higher stretch lengths. c) After application of the cholinergic blocking agent mecamylamine or after severance of the GS nerve, the Renshaw stretch response was abolished. d) The results lend some support to the hypothesis that RCs are triggered predominantly by large phasic motoneurones. The smaller tonic motoneurones seem to provide some supporting background input to the RCs.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-1106
    Keywords: Ramp-and-hold stretches ; Ia inhibitory interneurones ; Renshaw cells ; Reciprocal inhibition ; Recurrent facilitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of ramp stretches applied to triceps surae muscle on the discharge patterns of single Ia inhibitory interneurones, monosynaptically invaded from various nerves, were studied in either decerebrate or anesthetized cats. Interneurones which received direct excitatory Ia input from the stretched muscle exhibited augmented activity both during the dynamic and static phase of stretch, which was, however, interrupted by a transient inhibitory influence during the dynamic phase of stretch. The influences on Ia inhibitory interneurones, monosynaptically invaded from hamstring or tibial nerve, were exclusively inhibitory. These stretch-induced inhibitions were better demonstrable in decerebrate than in anesthetized preparations. The timing of the discharge patterns of additionally recorded Renshaw cells during stretch, and the disappearance or reduction of the above described inhibitory effects after administration of DHE, strongly support the idea that these inhibitory actions are caused by Renshaw inhibition. In Ia inhibitory interneurones, monosynaptically activated from the antagonistic peroneal nerve, stretch induced also pronounced inhibitory effects, which were most probably caused by mutual inhibition between Ia inhibitory interneurones. The suppression of agonistic Ia inhibitory interneurone activity below the tonic resting activity corresponded to an enhancement of the monosynaptic reflex amplitude of the antagonistic motoneurone pool. The findings suggest that normal orthodromic activation of Renshaw cells, and consequently the recurrent inhibition of the Ia inhibitory interneurones, is predominantly linked with rapid phasic, rather than slow tonic, motoneuronal firing. The functional role of this mechanism for the performance of rapidly alternating movements and the damping of ballistic agonist contractions is discussed.
    Type of Medium: Electronic Resource
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