Anatomic correlates of the face and oral cavity representations in the somatosensory cortical area 3b of monkeys

We determined the somatotopy of the face and the oral cavity representation in cortical area 3b of New World owl monkeys and squirrel monkeys. Area 3b is apparent as a densely myelinated strip in brain sections cut parallel t o the surface of flattened cortex. A narrow myelin-light septum that we hav e termed the "hand-face septum" separates the hand representation from the more lateral face and mouth representation. The face and oral cavity repres entation is further divided into a series of myelin-dense ovals. We show th at three ovals adjacent to the hand representation correspond to the upper face, upper lip, and chin plus lower lip, whereas three or four more rostra l ovals successively represent the contralateral teeth, tongue, and the ips ilateral teeth and tongue. Strips of cortex lateral and medial to the area 3b ovals, possibly corresponding to area 1 and area 3a, respectively, have similar somatotopic sequences. Although previous results suggest the existe nce of great variability within and across primate species, we conclude tha t the representations of the face and mouth are highly similar across indiv iduals of the same species, and there are extensive overall similarities ac ross these two species of New World monkeys. J. Comp. Neurol. 429:455-468, 2001. (C) 2001 Wiley-Liss, Inc.