Two cortical systems for directing movement.

It is argued that the cortical premotor areas are concerned with the conditions for action. Actions are based both on facts about the outside world and about the actions of the animal itself. Observations on monkeys (Macaca fascicularis, Macaca mulatta) suggest that the arcuate premotor area directs actions on the basis of visual cues about the outside environment and that the supplementary motor area directs actions on the basis of proprioceptive cues concerning the animal's own actions.