A REDEFINITION OF SOMATOSENSORY AREAS IN THE LATERAL SULCUS OF MACAQUE MONKEYS

The present investigation was designed to determine the organization o f somatosensory fields in the lateral sulcus of macaque monkeys using standard microelectrode recording techniques. Our results provide evid ence for two complete representations of the body surface. We term the se fields the second somatosensory area (SII) and the parietal ventral area (PV) because of their similarities in position, internal organiz ation, and relationship to anterior parietal fields, as described for SII and PV in other mammals, Areas SII and PV are mirror-symmetrical r epresentations of the body surface, sharing a common boundary at the r epresentations of the digits of the hand and foot, lips, and mouth. Th ese fields are located adjacent to the face representations of anterio r parietal fields (areas 3b, 1, and 2), and are bounded ventrally and caudally by other regions of cortex in which neurons are responsive to somatic or multimodal stimulation. The finding of a double representa tion of the body surface in the region of cortex traditionally designa ted as SII may explain conflicting descriptions of SII organization in macaque monkeys. In addition, the present study raises some questions regarding the designation of serial processing pathways in Old World monkeys, by suggesting that fields may have been confused in studies d emonstrating such pathways. We propose that SII and PV are components of a common plan of organization, and are present in many eutherian ma mmals.