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  • 1
    Electronic Resource
    Electronic Resource
    The importance of somatosensory information in triggering and scaling automatic postural responses in humans (1994)
    Springer
    Experimental brain research 101 (1994), S. 159-164 
    Details
    ISSN: 1432-1106
    Keywords: Posture ; Somatosensory ; Neuropathy EMG ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To clarify the role of somatosensory information from the lower limbs of humans in triggering and scaling the magnitude of automatic postural responses, patients with diabetic peripheral neuropathy and agematched normal controls were exposed to posterior horizontal translations of their support surface. Translation velocity and amplitude were varied to test the patients' ability to scale their postural responses to the magnitude of the translation. Postural response timing was quantified by measuring the onset latencies of three shank, thigh, and trunk muscles and response magnitude was quantified by measuring torque at the support surface. Neuropathy patients showed the same distalto-proximal muscle activation pattern as normal subjects, but the electromyogram (EMG) onsets in patients were delayed by 20–30 ms at all segments, suggesting an important role for somatosensory information from the lower limb in triggering centrally organized postural synergies. Patients showed an impaired ability to scale torque magnitude to both the velocity and amplitude of surface translations, suggesting that somatosensory information from the legs may be utilized for both direct sensory feedback and use of prior experience in scaling the magnitude of automatic postural responses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00243226
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Morphology of action potentials recorded from human nerves using microneurography (1996)
    Springer
    Experimental brain research 110 (1996), S. 308-314 
    Details
    ISSN: 1432-1106
    Keywords: Action potential morphology ; Human ; Muscle afferents ; Microneurography ; Conduction block
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study investigated the morphology of action potentials and the frequency of occurrence of the various waveforms encountered when using microneurography to record single-unit muscle afferent activity in humans. With 75% of the afferents recorded in this study (55 of 73 afferents), action potentials had a doublepeaked morphology. For action potentials with an initial, positive double peaked morphology, the relevant afferent conducts impulses past the microelectrode, with the second peak representing current fluctuations at the node of Ranvier proximal to the electrode. Accordingly, in the majority of recordings, the afferent is capable of conducting impulses to the spinal cord. The mean interpeak interval for these double-peaked units was 168 μs (range 90–310 μs). This represents marked prolongation of conduction time across the impaled internode. When the interpeak interval was relatively short (90–120 μs), the double peaked morphology could be recognized only if the low pass filter was high (≥10 kHz). The probability of recording a double peaked unit was the same whether the recording was acquired early or late in a 3-h experiment. Conduction block developed in 6 of 73 single units during the recordings. These findings indicate that the majority of isolated single afferents and, indeed, the majority of afferents within the relevant fascicle are capable of transmitting impulses across the recording site, even though conduction across the impaled internode is slow. Conduction block due to direct injury or pressure is relatively uncommon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228561
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Weak short-latency spinal projections to the long flexor of the human thumb (1997)
    Springer
    Experimental brain research 115 (1997), S. 165-168 
    Details
    ISSN: 1432-1106
    Keywords: Key words Monosynaptic reflex ; Muscle afferents ; Motor unit ; Thumb ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The human thumb is controlled by a muscle, flexor pollicis longus (FPL), that is unique among mammals and contributes to manual dexterity. The present study sought to define whether the spinal reflex circuitry for this muscle differed from that for an adjacent muscle (flexor carpi radialis, FCR). In peri-stimulus time histograms, short-latency, largely monosynaptic excitation produced by median nerve stimulation was significantly less frequent and significantly smaller for FPL motor units than FCR motor units. Thus the motoneurone pools of adjacent muscles differ in their spinal reflex accessibility. The reflex control of FPL may thus be achieved by supraspinal pathways rather than the traditional monosynaptic arc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00005677
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of muscle vibration on human position sense during movements controlled by lengthening muscle contraction (1991)
    Springer
    Experimental brain research 84 (1991), S. 631-634 
    Details
    ISSN: 1432-1106
    Keywords: Muscle vibration ; Kinesthesis ; Lengthening contraction ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Muscle vibration studies suggest that during voluntary movement limb position is coded by muscle spindle information derived from the lengthening, antagonist muscle. However, these investigations have been limited to movements controlled by shortening contractions. This study further examined this property of kinesthesia during movements controlled by lengthening contraction. Subjects performed a horizontal flexion of the right forearm to a mechanical stop randomly positioned at 30, 50 and 70° from the starting position. The movement was performed against a flexor load (1 kg) requiring contraction of the triceps muscle. Vision was occluded and movements were performed under three conditions: no vibration, vibration of the right biceps and vibration of the right triceps. The perceived position of the right forearm was assessed by instructing subjects to simultaneously match the right limb position with the left limb. Vibration of the shortening biceps muscle had no effect on limb matching accuracy. However, triceps vibration resulted in significant overestimation of the vibrated limb position (10–13°). The variability in movement distance was uninfluenced by muscle vibration. During movements controlled by lengthening contraction, there is a concurrent gamma dynamic fusimotor input that would enhance primary afferent discharge. Despite this additional regulating input to the muscle spindle, it appears that muscle spindle information from the lengthening muscle is important for the accurate perception of limb movement and/or position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230975
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of agonist/antagonist muscle vibration on human position sense (1990)
    Springer
    Experimental brain research 81 (1990), S. 573-580 
    Details
    ISSN: 1432-1106
    Keywords: Muscle spindles ; Agonist/antagonist muscle ; Forearm ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary During voluntary movement, muscle spindles of both the agonist and antagonist muscles potentially can supply information about position of the limb. Muscle vibration is known to increase muscle spindle discharge and cause systematic distortions of limb position sense in humans. The following two experiments attempted to examine these contributions by separately vibrating over the triceps and biceps muscles during forearm positioning. In the first experiment, subjects performed a horizontal flexion or extension of the right arm to a mechanical stop randomly positioned at 20, 40 or 60°. Vision was occluded and vibration was applied to the right arm. The perceived position of the right limb was assessed by instructing subjects to simultaneously match the right arm position with the left limb. Vibration of the shortening, agonist muscle had no effect on limb matching accuracy. However, antagonist muscle vibration resulted in a significant overestimation of the vibrated limb position by 6–13°. The procedures for the second experiment were similar to the first, except that movements of the right limb were self-terminated and only flexion movements were performed. A screen was mounted over the arms and subjects were instructed to move the right arm until it was positioned beneath a marker on the screen. Vibration of the shortening agonist muscle had no effect on either the positioning accuracy of the right limb or matching accuracy of the left limb. However, antagonist muscle vibration resulted in significantly shorter movements (6–10°) by the right limb and an overestimation of right limb position by the left, matching limb. These findings support the hypothesis that muscle spindle afferent information from the lengthening antagonist muscle contributes to limb position sense during voluntary movement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02423506
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  • 6
    Electronic Resource
    Electronic Resource
    The effects of stochastic galvanic vestibular stimulation on human postural sway (1999)
    Springer
    Experimental brain research 124 (1999), S. 273-280 
    Details
    ISSN: 1432-1106
    Keywords: Key words Vestibular system ; Posture control ; Balance ; Cross-spectral analysis ; Coherency ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Galvanic vestibular stimulation serves to modulate the continuous firing level of the peripheral vestibular afferents. It has been shown that the application of sinusoidally varying, bipolar galvanic currents to the vestibular system can lead to sinusoidally varying postural sway. Our objective was to test the hypothesis that stochastic galvanic vestibular stimulation can lead to coherent stochastic postural sway. Bipolar binaural stochastic galvanic vestibular stimulation was applied to nine healthy young subjects. Three different stochastic vestibular stimulation signals, each with a different frequency content (0–1 Hz, 1–2 Hz, and 0–2 Hz), were used. The stimulation level (range 0.4–1.5 mA, peak to peak) was determined on an individual basis. Twenty 60-s trials were conducted on each subject – 15 stimulation trials (5 trials with each stimulation signal) and 5 control (no stimulation) trials. During the trials, subjects stood in a relaxed, upright position with their head facing forward. Postural sway was evaluated by using a force platform to measure the displacements of the center of pressure (COP) under each subject’s feet. Cross-spectral measures were used to quantify the relationship between the applied stimulus and the resulting COP time series. We found significant coherency between the stochastic vestibular stimulation signal and the resulting mediolateral COP time series in the majority of trials in 8 of the 9 subjects tested. The coherency results for each stimulation signal were reproducible from trial to trial, and the highest degree of coherency was found for the 1- to 2-Hz stochastic vestibular stimulation signal. In general, for the nine subjects tested, we did not find consistent significant coherency between the stochastic vestibular stimulation signals and the anteroposterior COP time series. This work demonstrates that, in subjects who are facing forward, bipolar binaural stochastic galvanic stimulation of the vestibular system leads to coherent stochastic mediolateral postural sway, but it does not lead to coherent stochastic anteroposterior postural sway. Our finding that the coherency was highest for the 1- to 2-Hz stochastic vestibular stimulation signal may be due to the intrinsic dynamics of the quasi-static postural control system. In particular, it may result from the effects of the vestibular stimulus simply being superimposed upon the quiet-standing COP displacements. By utilizing stochastic stimulation signals, we ensured that the subjects could not predict a change in the vestibular stimulus. Thus, our findings indicate that subjects can act as ”responders” to galvanic vestibular stimulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050623
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