Analysis of slow cortical potentials preceding self-paced hand movements in the monkey.

Cortical potentials related to the self-paced “voluntary” hand movement were recorded in unanesthetized, freely moving monkeys with the electrodes implanted chronically on the surface and in the depth of the cortex, and analyzed with the method of electronic averaging. Prior to the movement, surface negative — deep positive slow potential changes appeared in the motor and premotor cortices contralateral to the moving hand. The potential changes started about 1 s before the hand movement and increased gradually to about 100 ms before the movement. The contours of the potential changes preceding the movement were remarkably constant in daily recording for several weeks. Based on the laminar field potential analyses of cortical evoked potentials made in previous acute experiments, the slow potential was interpreted to be due to the currents of slowly increasing EPSPs that were generated in superficial parts of the cortical pyramidal neurons via certain thalamocortical projections. The EPSPs would activate the neurons in the motor and premotor cortices and contribute to the initiation of voluntary movement.