Somesthetic function of supplementary motor area during voluntary movements

To clarify the somesthetic functions of the supplementary motor area (SMA), we recorded the cortical potentials following the median nerve electric stimulation directly from the SMA and investigated the modulation caused by voluntary movements in two patients with intractable SMA seizures. The evoked potentials over the SMA consisted of positive (61.5ms) and negative (100.0 ms) peaks, which were enlarged by voluntary movements of the stimulated hand. The present finding is in strong contrast with the attenuation (gating) of the response at the primary sensorimotor area (SM1) and suggests that the voluntary movements differently modulate the somatosensory functions of SMA and SM1.