Supplementary motor area and premotor area of monkey cerebral cortex: functional organization and activities of single neurons during performance of a learned movement.

In the conscious, behaving monkey trained to perform a motor task either self-paced or involving light cues, a restricted area responsive during performance of the task can be found in cytoarchitectonic area 6 at the level of the concavity of the arcuate sulcus. Within this area, different groups of neurons can be identified in relation to experimental variables. First a group related in its activity to specific aspects of movement performance. Second, a group associated with movements and visual events, and third, a group modulated in its activity throughout the execution of the task. A few neurons are related to visual cues only. In the first group, a subpopulation exists of neurons active with movements of either extremity; this group resembles similar neurons in SMA. Such neurons can be associated with proximal or distal movements suggesting PM is not an area involved mainly in the maintenance of body posture. The PM may function as a visuomotor integration center as evidenced by the large number of neurons influenced by visual aspects of the tasks. This is also suggested by findings in lesion studies in monkeys and man. Studies in conscious monkeys and man point to a role for PM in motor learning, when a new motor program is established or a previously learned one modified.