Activity of precentral neurons during torque-triggered hand movements in awake primates

In monkeys performing a handle-repositioning task involving primarily wrist flexion-extension (F-E) movements after a torque perturbation 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 joint 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 sensory stimuli and the motor responses. Visual stimuli, presented simultaneously with torque perturbations, 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.