Cortical field potentials associated with hand movements triggered by warning and imperative stimuli in the monkey.

Monkeys were trained to move the hand in response to imperative visual stimulus (IS) given 1 s after warning visual stimulus (WS). With implanted electrodes in the cortices, surface-negative (s-N), depth-positive (d-P) sustained potentials between WS and IS were recorded in the prefrontal, premotor and supplementary motor areas in both hemispheres, and gradually increasing s-N, d-P potentials were seen in the forelimb areas of motor and somatosensory cortices contralateral to the hand. It is suggested that the sustained and gradually increasing potentials are related respectively to cortical activities associated with expectation and anticipation of the IS, and to those with a preparatory process for the movement. The latter appeared to be similar to the case of self-paced movements. These potentials may correspond respectively to the early and late components of CNV in the human.