The ventral primary somatosensory cortex of the primate brain: Innate neural interface for dexterous orofacial motor control

Studies using nonhuman primates have made marked contributions to our understanding of the anatomy and function of the primary somatosensory cortex (SI). Its ventral or inferolateral part (vSI) represents orofacial structures, such as the lips, periodontium, tongue, palate, chewing musculature, etc. This brain region is neurally interconnected with the ventral part of the primary motor cortex that executes voluntary orofacial movements. Also within the vSI, regions representing different orofacial structures are interconnected with each other. Therefore, in self-generated actions, the vSI plays a crucial role in coordinating motor control of a set of structures that are functionally related: the vSI serves as an interface not only between orofacial structures and the external environment but also between the orofacial structures themselves. In this article, we will chiefly review the neuroanatomical and neurophysiological studies on the monkey vSI from the viewpoint of motor control or stereognostic ability. Future physiological studies that analyze the spatiotemporal spiking pattern of vSI neurons during various behaviors in monkeys should reveal the principles of information coding and might significantly benefit future applications of brain-machine-brain interface (BMBI) technology.