BILATERAL RECIPROCAL ORGANIZATION IN MAN - FOCUS ON IA INTERNEURON

The H reflex of flexor carpi radialis and radial-induced reciprocal in hibition were recorded in normal subjects during conditioning stimulat ion of the contralateral median or radial nerves. It was found that st imulation of the contralateral median nerve enhanced the degree of rec iprocal inhibition exerted by the radial nerve on the median nerve, wh ile contralateral radial nerve stimulation reduced the reciprocal inhi bition exerted by the extensor on the flexor. In two subjects in which a pure extensor H reflex was recorded specular features were observed following contralateral median and radial stimulation. These findings are considered to be the electrophysiological manifestation of contra lateral modulation of reciprocal inhibition, which is likely to act at the level of the IA interneurone.