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  • 1
    Digitale Medien
    Digitale Medien
    Postural electromyographic responses in the arm and leg following galvanic vestibular stimulation in man (1993)
    Springer
    Experimental brain research 94 (1993), S. 143-151 
    Details
    ISSN: 1432-1106
    Schlagwort(e): Vestibular system ; Galvanic stimulation ; Posture ; Electromyogram ; Human
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Application of a small (around 1 mA), constant electric current between the mastoid processes (galvanic stimulation) of a standing subject produces enhanced body sway in the approximate direction of the ear behind which the anode is placed. We examined the electromyographic (EMG) responses evoked by such stimulation in the soleus and in the triceps brachii muscles. For soleus, subjects stood erect, with their eyes closed, leaning slightly forward. The head was turned approximately 90° to the right or left relative to the feet. In averaged records (n=40), current pulses of 25 ms or longer modulated the EMG in a biphasic manner: a small early component (latency 62±2.4 ms, mean ± SEM) was followed by a larger late component (latency 115±5.2ms) of opposite sign, which was appropriate to produce the observed body sway. The early component produced no measurable body movement. Lengthening the duration of the stimulus pulse from 25 to 400 ms prolonged the late component of the response but had little effect on the early component. Short- and long-latency EMG responses were also evoked in the triceps brachii muscle if subjects stood on a transversely pivoted platform and had to use the muscle to maintain their balance in the anteroposterior plane by holding a fixed handle placed by the side of their hip. The latency of the early component was 41±2.6 ms; the latency of the late component was 138±4.3 ms and was again of appropriate sign for producing the observed body sway. Galvanic stimulation evoked no comparable responses in either triceps brachii or soleus muscles if these muscles were not being used posturally. The responses were most prominent if vestibular input provided the dominant source of information about postural stability, and were much smaller if subjects lightly touched a fixed support or opened their eyes. The difference in latency between the onset of the early component of the response in arm and leg muscles suggests that this part of the response uses a descending pathway which conducts impulses down the spinal cord with a velocity comparable with that of the fast conducting component of the corticospinal tract. The late component of the EMG response occurs earlier in the leg than the arm. We suggest that it forms part of a patterned, functional response which is computed independently of the early component.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00230477
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  • 2
    Digitale Medien
    Digitale Medien
    Primary orthostatic tremor: further observations in six cases (1992)
    Springer
    Journal of neurology 239 (1992), S. 209-217 
    Details
    ISSN: 1432-1459
    Schlagwort(e): Orthostatic tremor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The clinical and physiological features of six new patients with primary orthostatic tremor are described. We suggest that use of the term primary orthostatic tremor be confined to the clinical syndrome in which unsteadiness when standing is the predominant complaint and accompanied by characteristic electrophysiological findings of a rapid (frequency around 16 Hz), regular leg tremor which is not influenced by peripheral feedback, is synchronous between homologous leg muscles, and in certain postures of the upper limbs, between muscles of the arm and leg. The fast frequency of muscle activity in primary orthostatic tremor of the legs causes unsteadiness when standing (presumably due to partially fused muscle contraction) but only a fine ripple of muscle activity is visible. In contrast, the slower frequency of other leg tremors, for example essential tremor, results in obvious leg movement which is evident in many leg postures, is variable over time and can be reset by a peripheral nerve stimulus. Essential tremor and orthostatic tremor do not respond to the same therapies, suggesting differences in the pharmacological profiles of the two conditions. Accordingly, there are clinical, physiological and pharmacological differences between primary orthostatic and essential tremor. Whether these factors are sufficient to regard these tremors as separate conditions is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00839142
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  • 3
    Digitale Medien
    Digitale Medien
    Motor responses evoked by magnetic brain stimulation in psychogenic limb weakness: diagnostic value and limitations (1992)
    Springer
    Journal of neurology 239 (1992), S. 251-255 
    Details
    ISSN: 1432-1459
    Schlagwort(e): Magnetic brain stimulation ; Psychogenic weakness ; Central weakness ; Corticospinal tract function
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The latencies and amplitudes of responses evoked by magnetic brain stimulation (magnetic evoked potentials, MEP) in the first dorsal interosseus and the anterior tibial (TA) muscles were investigated in 15 patients with psychogenic limb weakness and in 50 patients with limb weakness due to established organic central nervous system disease. Of the patients with psychogenic limb weakness, 3 presented with upper limb monopareses, 2 with lower limb monoparesis, 4 with hemipareses, 4 with parapareses and 2 with paraparesis. All patients with psychogenic weakness had MEP in arm and leg muscles with latencies within the normal range. MEP amplitudes were also normal except for 1 patient in whom the response amplitude in the TA of the plegic limb was reduced. In patients with limb weakness due to established organic disease, MEP were frequently but not invariably abnormal. In patients with plegic (i.e. completely paretic, MRC grade 0) muscles due to organic disease, MEP always were clearly abnormal. Normal MEP were sometimes elicited from paretic muscles, more commonly in association with cerebral hemisphere lesions than with spinal lesions. We conclude that psychogenic limb weakness is associated with normal MEP. However, normal MEP in mildly paretic muscles do not definitely exclude organic pathology.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00810346
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