INPUT-OUTPUT ORGANIZATION IN THE HAND AREA OF THE HUMAN MOTOR CORTEX

The primate motor cortex consists of efferent zones which receive sens ory information from a portion of limb in close anatomical relation to the muscle to which they project. To investigate a similar input-outp ut relation in humans, we studied the effect of tactile stimuli on the size of motor evoked potentials (MEPs) elicited by transcranial magne tic and electrical stimulation. For tactile stimuli we applied air to the skin. The sizes of MEP of 3 finger muscles (flexor pollicis brevis , first dorsal interosseous, and abductor digiti minimi) with and with out air stimuli were compared. Air stimuli applied to the tip of one f inger facilitated mainly the magnetically evoked MEP of a muscle attac hed to that finger. A less obvious facilitatory effect was observed wh en giving stimuli on the dorsal aspect of the hand. Air stimuli had no facilitatory effect on electrically evoked MEPs. In one subject, ther e was no facilitatory effect even to magnetically evoked MEPs. In this subject, D-waves had the lowest threshold for magnetic and electrical stimulation. These results suggested that the effect was produced at the cortical level. This effect may correspond to the input-output rel ation found in the primate motor cortex.