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

Abstract

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 to the surface of flattened cortex. A narrow myelin-light septum that we have termed the "hand-face septum" separates the hand representation from the more lateral face and mouth representation. The face and oral cavity representation is further divided into a series of myelin-dense ovals. We show that three ovals adjacent to the hand representation correspond to the upper face, upper lip, and chin plus lower lip, whereas three or four more rostral ovals successively represent the contralateral teeth, tongue, and the ipsilateral 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 existence of great variability within and across primate species, we conclude that the representations of the face and mouth are highly similar across individuals of the same species, and there are extensive overall similarities across these two species of New World monkeys.

Cortical network for representing the teeth and tongue in primates

“…The recordings in squirrel and owl monkeys (Jain et al, 2001), as well as those more recently in galagos (data not shown), revealed additional representations of the tongue and teeth in cortex adjoining area 3b (Fig. 1).…”

“…However, later it became apparent that the histological boundaries of area 3b were quite visible in appropriately stained sections cut parallel to the cortical surface after cortex had been artificially flattened so that dorsomedial and ventrolateral portions of area 3b were forced into the same plane (Tootell et al, 1985). Such brain sections in owl and squirrel monkeys revealed that area 3b extends much further rostrally than ever suspected, and that the myelin-dense architecture of area 3b contains a number of interruptions that relate to somatotopy (Jain et al, 2001). First, there is a long mediolateral band of dense myelination that extends from near the medial wall to near the lateral fissure.…”

“…C: Part of a brain section from unfolded and flattened cortex cut parallel to the surface and stained for myelin to show the F and O ovals of area 3b in an owl monkey. Holes in the hand representation and the F2, F3, O1, and O2 ovals are microlesions placed to identify recording sites (see Jain et al, 2001). The hand is represented in cortex just above the F1-F3 ovals.…”

Intraoperative optical imaging of human face cortical topography: a case study

“…Cortical magnification: Although somatosensory cortical magnification factors (CMF, mm cortex/mm skin) in non-human primates have been studied extensively [19,20,[22][23], few data exist on somatosensory CMFs in the human, especially at the sub-millimeter scale. We estimated a CMF of 0.36 mm/cm of facial skin.…”

The Ventral Primary Somatosensory Cortex of the Primate Brain: Innate Neural Interface for Dexterous Orofacial Motor Control

“…This "hand-face border" can be detected as a myelin-light septum in brain sections cut parallel to the cortical surface. Further laterally, myelin-dense ovals were shown to indicate anatomical modules that correspond to representations of different orofacial structures in both New [16,17] and Old World monkeys [13,15]. In New World monkeys, the myelin-dense ovals are arranged in a rostrocaudal direction and extend to the ventral frontal lobe.…”