Distribution of potentials preceding visually initiated and self-paced hand movements in various cortical areas of the monkey.

A monkey was trained to lift a lever by its hand in response to a light stimulus or at self-pace; field potentials preceding, respectively, visually initiated and self-paced movements were recorded in various areas on the dorso-lateral and mesial surface of the cerebral hemisphere, with electrodes implanted chronically on the surface and at 2.5-3.0 mm depth of respective cortical areas. Slowly rising, surface-negative, depth-positive (s-N, d-P) potentials were obtained prior to the self-paced movement in the bilateral premotor cortex, and in the contralateral forelimb motor, somatosensory and mesial premotor areas, resembling 'readiness potentials'. Potentials preceding the visually initiated movement occurred in more cortical areas than the self-paced movement, with characteristic potential features to respective areas. In bilateral prefrontal and prestriate cortices, early s-P, d-N and following s-N, d-P potentials were obtained. Only early s-P, d-N potentials occurred bilaterally in the premotor cortex. In the contralateral forelimb motor area, early s-P, d-N and late s-N, d-P premovement potentials were observed. In the mesial premotor area, s-P, d-N and following s-N, d-P potentials were recorded at a little longer latency and with smaller amplitude than in the motor cortex.