Sensory responses in motor cortex neurons during precise motor control.

Precentral neurons whose activity changed with precisely controlled small supination-pronation movements almost invariably showed sensory responses to small perturbations which pronated or supinated the forearm in conscious monkeys. Conversely, most units failing to show changes with small movements but being recruited with large ballistic movements were unaffected by these kinesthetic inputs. Moreover, perturbations which yielded intense short-latency unit responses when delivered during postural stability usually failed to modify unit activity when delivered during a ballistic movement. It is suggested that sensory feedback continuously modulates motor cortex neuron discharge during accurate positioning and precise fine movement, whereas during ballistic movements such modulation is greatly attenuated.