Reexamination of the force relationship of cortical cell discharge patterns with conditioned wrist movements.

Single unit recordings were obtained from 103 precentral cortical cells whose activity was related to an alternate wrist flexion-extension task in monkeys. Although the task was carried out under different loads only a weak relationship between cortical cell firing rates and static force levels was observed for force in one direction. A large change in firing rate occurred, however, when direction of force shifted as a result of a change in the predominant activity between extensor and flexor muscles. The firing patterns of the observed cortical cells suggest that the motor cortex is involved in specifying the muscles to be activated for a given movement and not the level of force to be produced by these muscles. During the dynamic phase of the movement little change in cortical cell firing pattern was observed for large changes in the rate of change of force. Motor cortex cell firing patterns appear to be unrelated to the large values of rate of change of force seen in this experiment.