ACTIVITY OF PRECENTRAL NEURONS DURING TORQUE-TRIGGERED HAND MOVEMENTS IN AWAKE PRIMATES

In monkeys performing a handle-respositioning task involving primarily wrist flexion-extension (F-E) movements after a torque pertubation was delivered to the handle, single units were recorded extracellularly in the contralateral precentral cortex. Precentral neurons were identified by passive somatosensory stimulation, and were classified into five somatotopically organized populations. Based on electromyographic recordings, it was observed that flexors and extensors about the wrist were specifically involved in the repositioning of the handle while many other muscles which act at the wrist and other forelimb joints were involved in the task in a supportive role. In precentral cortex, all neuronal responses observed were temporally correlated to both the stimuli and the motor responses. Visual stimuli, presented simultaneously with torgue pertubations, did not affect the early portion of cortical responses to such torque perturbations. In each of the five somatotopically organized neuronal populations, task-related neurons as well as task-unrelated ones were observed. A significantly larger proportion of wrist (F-E) neurons was related to the task, as compared with the other, nonwrist (F-E) populations. The above findings were discussed in the context of a hypothesis for the function of precentral cortex during voluntary limb movement in awake primates. This hypothesis incorporates a relationship between activities of populations of precentral neurons, defined with respect to their responses to peripheral events at or about single joints, and movements about the same joint.