Relation of motor cortex neurons to precisely controlled and ballistic movements.

A visual pursuit-tracking paradigm was used for training monkeys to position a handle within a small zone and rotate it by pronation-supination movements. Motor cortex unit discharge was examined in relation to movements carried out in this situation, with particular attention to large ballistic movements as compared to small precisely controlled movements. Intense unit discharge was found to occur with even the smallest movements made to achieve accurate positioning of the handle. Within the group of motor cortex pyramidal tract neurons (PTNs), slowly conducting tonically discharging PTNs showed the most selective relations to these small precisely controlled movements.