Participation of precentral neurons in somatically and visually triggered movements in primates.

Monkeys were trained to perform somatically and visually triggered wrist flexion-extension (F-E) movements. Extracellular unit recordings were made in the contralateral precentral forelimb area. These neurons were identified as being best related to particular single forelimb joints by their responses to passive somatosensory stimulation and to the determining effects of local intracortical microstimulation. It was found that almost 60% of single-joint related cells participated in both somatically and visually triggered movements. All wrist (F-E) neurons responded reciprocally while non-wrist (F-E) neurons had reciprocal as well as bidirectional responses to the oppositely directed visual and somatic perturbations. Somatically related responses and visually related responses were both uniformly distributed throughout the vertical layers of precentral cortex. With respect to horizontal spatial arrangements, multiple clusters of reciprocally and bidirectionally responsive neurons were intermingled. This latter finding supports the concept of a context-sensitive organization for motor control within precentral cortex.