Voluntary muscle release is not accompanied by H-reflex inhibition in patients with upper moto neuron lesions

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Abstract

Changes in excitability of the soleus (Sol) monosynaptic reflex are were investigated in spastic subjects, affected by amyotrophic lateral sclerosis (ALS), upon voluntary relaxation of tonic contraction of triceps surae muscle. Force and electromyograms (EMG) were recorded during triceps release, performed in response to an acoustic signal, in a reaction-time (RT) situation. Sol H-reflex was evoked at random during the task, and its amplitude was referred in time to the end of Sol EMG. At variance with the results for the same task in normal subjects, it was found that in ALS patients the RTs of the termination of EMG were longer than those of the beginning of the EMG, the decrease in force was prolonged and perturbed owing to intercurrent clonus-like EMG activity, and the H-reflex did not undergo the expected profound inhibition. It is suggested that the absence of the activation of presynaptic inhibitory mechanisms by the descending command to release brings about major disorders in voluntary muscle relaxation.

Original languageEnglish
Pages (from-to)177-181
Number of pages5
JournalNeuroscience Letters
Volume61
Issue number1-2
DOIs
Publication statusPublished - Oct 24 1985

Keywords

  • H-reflex
  • man
  • motor termination
  • presynaptic inhibition
  • spasticity

ASJC Scopus subject areas

  • Neuroscience(all)

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