Recording of movement-related potentials from scalp and cortex in man

Movement-related cortical potentials (MRPs) were recorded from scalp electrodes in 8 normal volunteers and from chronically implanted subdural electrodes in 7 patients who were being evaluated for surgical treatment of epilepsy. From subdural electrodes, a clearly defined, extremely localized slow negative potential preceding the voluntary movement of the middle finger (Bereitschaftspotential, BP) was recorded in the contralateral and ipsilateral hand sensorimotor areas. The negative slope (NS') began approximately 250 to 400 ms before EMG onset and was recorded exclusively from the contralateral hand sensorimotor area. Both BP and NS' were maximum in the hand motor area. Although a negative slope was recorded also from the supplementary motor area, whether that particular slope corresponded to BP or NS', or both, could not be determined. Three kinds of progressively steeper negative potentials starting around the onset of the EMG were identified: (1) the 'hand motor potentials' which were seen in the contralateral hand motor area and started immediately before EMG onset and peaked 130 +/- 32 ms after EMG onset; (2) the 'hand somatosensory potentials' seen in the contralateral hand somatosensory area which started simultaneously or immediately after the EMG onset; and (3) the 'vicinity potentials' seen in the immediate surroundings of the contralateral hand area and which started after the EMG onset. The 'hand motor potentials' had the highest amplitude. From these findings, we concluded that bilateral hand sensorimotor areas and the supplementary motor area participate in the 'preparation' of movements, but that mainly the contralateral cortex generates the discharges necessary to produce the actual movement.