The Motor Cortex and the Coding of Force

Abstract

The relation of cellular activity in the motor cortex to the direction of two-dimensionalisometric force was investigated under dynamic conditions in monkeys. A task was designedso that three force variables were dissociated:the force exerted by the subject, thenet force, and the change in force. Recordings of neuronal activity in the motor cortexrevealed that the activity of single cells was directionally tuned and that this tuning wasinvariant across different directions of a bias force. Cell activity was not related to thedirection of force exerted by the subject, which changed drastically as the bias forcechanged. In contrast, the direction of net force, the direction of force change, and thevisually instructed direction all remained quite invariant and congruent and could be thedirectional variables, alone or in combination, to which cell activity might relate.