Evidence of a contralateral motor influence on reciprocal inhibition in man.

The role of contralateral movement on both H reflex and reciprocal inhibition was studied. In normal men H reflex was induced by median nerve stimulation. Reciprocal inhibition was achieved through stimulation of the antagonist radial nerve. On this basis the effects of contralateral arm movement were analyzed. Furthermore the putative influence of exteroceptive origin was also verified by means of digit stimulation. Results showed that contralateral arm movement did not affect H reflex amplitude; on the contrary, it was able to enhance reciprocal inhibition induced by extensors on flexors. Study of cutaneous afferents demonstrated that contralateral digit stimulation failed to elicit modifications on both H reflex and reciprocal inhibition. On the other hand, ipsilateral digit stimulation lowered H reflex amplitude and increased the degree of reciprocal inhibition. Experimental findings underline the possibility that an informational array reaches the contralateral IA interneuron: therefore a mutual (bilateral) interaction among IA interneurones may accordingly be hypothesised.