Effects of hand movement path on motor cortical activity in awake, behaving rhesus monkeys

Neuronal activity was studied in the primary (M1), supplementary (M2), dorsal premotor (PMd), and ventral premotor (PMv) cortex of awake, behaving rhesus monkeys. The animals performed forelimb movements to three targets, each approached by three different types of trajectories. With one trajectory type, the monkey moved its hand straight to the target, with another, the path curved in a clockwise direction, and with a third, the path curved in a counter-clockwise direction. We examined whether neuronal activity in these areas exclusively reflects a hand movement's net distance and direction or, alternatively, whether other factors also influence cortical activity. It was found that neuronal activity during all phases of a trial reflects aspects of movement in addition to target location. Among these aspects may be selection of an integrated motor act from memory, perhaps specifying the entirety of a path by which the hand moves to a target.