Comparative study of cerebral cortical potentials associated with voluntary movements in monkey and man.

Eight monkeys (Macaca mulatta) were taught to squeeze and release a handgrip. The movement simulated the brisk squeeze of a hand dynamometer performed by 7 human subjects. Monkey. During the performance of the voluntary movements, slow cortical potentials (motor potentials or MPs) were studied with monopolar, surface bipolar, transcortical and intracortical recordings. A survey of the dorsal expanse of cerebral cortex showed that the contralateral motor hand area, somatosensory hand area and area 6 adjacent to the supplementary motor area became active with movement. MPs also were seen in the motor and somatosensory cortex medial to the hand area, but we concluded that those potentials were probably related to adventitious movements in the arm and leg. That area 6 became active with movement was further verified with extracellular unit recording; the behavior of area 6 units was compared with that recorded from units in the motor hand area. Using simultaneous transcortical recordings a sequence of cortical activation was observed in those areas generating an MP. The motor hand area became active first, followed in turn by area 6 and the somatosensory hand area. The monosynaptic cortico-cortical connections of the motor hand area were studied with autoradiographic and horseradish peroxidase techniques and compared to the distribution of the MP. The hand area demonstrated reciprocal connectivity with portions of the somatosensory hand area, the supplementary motor area in area 6 and the cortex adjacent to the intraparietal sulcus. The distribution of the MPs correlated with the connectivity to the supplementary motor and somatosensory areas. Our physiologic studies did not adequately investigate the area adjacent to the intraparietal sulcus. Man. Motor potentials were studied using surface bipolar recordings with closely spaced electrodes (inter-electrode distances 1 cm or 2 cm). Recordings were made directly from the cortex in one subject studied under local anesthesia during an operation for epilepsy, and epidurally in 6 subjects in whom epidural electrode arrays had been inserted for the purpose of localizing an epileptogenic focus. Similar to the findings in the animals, MPs were recorded from the contralateral motor and somatosensory hand area with activity in motor cortex appearing first; area 6 just anterior to the motor hand area probably also generated a response. In addition, a locally generated potential not seen in monkey was recorded anterior to area 6. This difference in response distribution is viewed as possibly relating to the different significance which the seemingly comparable hand movements have for the animal and human subjects. No response was seen in motor and somatosensory hand area with ipsilateral movements. We have no information for the anteriorly recorded response with ipsilateral movement.