PRESYNAPTIC INHIBITION COMPARED WITH HOMOSYNAPTIC DEPRESSION AS AN EXPLANATION FOR SOLEUS H-REFLEX DEPRESSION IN HUMANS

The H-reflex is depressed for seconds if elicited following a single H -reflex or train of H-reflexes. Presynaptic inhibition from flexor aff erents (tibialis anterior) onto soleus Ia afferents elicited by either single or trains of stimuli had no effect on the soleus H-reflex on a time scale of seconds. Postsynaptic inhibition was also excluded by m agnetic stimulation tests that showed that the excitability of the mot oneuron pool was not changed at latencies within a range of seconds. H omosynaptic depression localized at the presynaptic terminal seems to be the mechanism behind the H-reflex depression in humans.