Patterns of early and late discharges in somatotopically identified precentral neurons in awake monkeys in response to somatic inputs.

Extracellular recordings were made of single neurons in precentral cortex of awake monkeys. These neurons were somatotopically identified with respect to their responses to inputs from single joints or their somatic surround. Many of these neurons exhibited early (less than 50 ms) and late (greater than 50 ms) discharges in response to flexion or extension torques delivered about the wrist. With the monkey in a mode requiring opposition to the injected torque, all responsive neurons showed a parallel excitatory or inhibitory modification in the early and late discharges. This was true both for cells identified as wrist (flexion-extension) neurons and those identified as nonwrist (flexion-extension) neurons. These findings indicate that the reflex and voluntary components of percentral discharge invariably show a congruent functional response to a torque disturbance, for this particular instruction set.