Double representation of the body surface within cytoarchitectonic area 3b and 1 in “SI” in the owl monkey (aotus trivirgatus)

Abstract

Microelectrode multiunit mapping studies of parietal cortex in owl monkeys indicate that the classical "primary" somatosensory region (or "SI") including the separate architectonic fields 3a, 3b, 1, and 2 contains as many as four separate representations of the body rather than one, An analysis of receptive field locations for extensive arrays of closely placed recording sites in parietal cortex which were later related to cortical architecture led t o the following conclusions: (1) There are two large systematic representations of the body surface within "SI." Each is activated by low threshold cutaneous stimuli; one representation is coextensive with Area 3b and the other with Area 1. (2) While each of these representations contains regions of cortex with topological or "somatotopic" transformations of skin surface, the representations have many discontinuities where adjoining skin surfaces are not adjoining in the representations. Thus, the representations can be considered as composites of somatotopically organized regions, but cannot be accurately depicted by simple continuous homunculi. Lines of discontinuity often cut across dermatomes and seldom follow dermatomal boundaries, i.e., neither cutaneous representation constitutes a systematic representation of dermatomal skin fields. (3) While the two cutaneous fields are basically similar in organization and are approximate mirror images of each other, they differ in important details, i.e., lines of discontinuity in the representations and the sites of representations of different specific skin surfaces differ significantly in the two representations. ( 4 ) The two cutaneous representations also differ in size and in the relative proportions of cortex devoted to representation of various body parts. Because the proportions in each representation differ, they cannot both be simple reflections of overall peripheral innervation density. ( 5 ) All or part of Area 2 contains a systematic representation of deep body structures.These conclusions are consistent with a view of the anterior parietal region as containing functionally distinct fields a t least partially related to different subsets of receptor populations and coding or representing different aspects of somatic sensation. We suggest that the "SI" region of primates be redefined as a parietal somatosensory strip, the Area 1 representation as the posterior cutaneous field, and, for reasons of probable homology with "SI" of other mammals, the Area 3b representation as SI proper.

Cortical network for representing the teeth and tongue in primates

“…First, the puzzle has been resolved of why primary somatosensory cortex of monkeys includes four distinct architectonic fields, area 3a, 3b, 1, and 2 of Brodmann (1909). Rather than these fields being a part of a single primary area, S1, as originally claimed, each of these fields contains a separate representation of body receptors (Merzenich et al, 1978), and each is a functionally distinct area (for review, see Kaas, 2004). Only area 3b corresponds to S1 as described in most nonprimate mammals (Kaas, 1983), and area 3b receives activating inputs from tactile mechanoreceptors via the ventroposterior (VP) nucleus of the somatosensory thalamus.…”

“…Early microelectrode mapping studies of the somatotopy of area 3b in New World owl monkeys (Merzenich et al, 1978) and squirrel monkeys (Sur et al, 1982) and Old World macaque monkeys (Nelson et al, 1980) did not disclose the full extent of the field because the ventrolateral portion of area 3b, where the tongue and teeth are represented, is less accessible, and because there was less interest in the representation of the oral structures. In addition, it was never very certain how far area 3b extended ventrolaterally and rostrally, as histological distinctions are best made in the most favorable plane of section, and the sagittal or near sagittal planes that best revealed the boundaries of dorsomedial area 3b were not suitable for ventrolateral 3b.…”

“…First, there is a long mediolateral band of dense myelination that extends from near the medial wall to near the lateral fissure. This band constitutes the portion of 3b that represents the body from tail to hand in a mediolateral sequence that has been described in great detail (Merzenich et al, 1978;Sur et al, 1982). A narrow myelin-poor septum cuts across the lateral margin of this band to separate the representation of the body from that of the face and oral skin (Fig.…”

Analysis of Retinotopic Maps in Extrastriate Cortex

“…However, in a number of instances, nearby cortical locations clearly represent disparate points on the sensory surface, in contrast to what we claimed was universally the case in visual cortex. For example, there are often sharp discontinuities in somatosensory cortex at the borders between different body parts; as one crosses from one digit representation into the adjoining digit representation, receptive fields suddenly jump to the next digit without any overlap (Merzenich et al, 1978). Similar discontinuities appear at the boundary between the representation of the arm and the face.…”

Transcranial Magnetic Stimulation to Investigate Motor Cortical Circuitry and Plasticity in Spinal Cord Injury

“…However, there is substantial evidence to indicate that so matosensory cortices are promising targets for inducing plasticity in these circuits. Decades of primate research have demonstrated the propensity for plasticity in somatosensory cortex that follows experience or practiced behaviour [107,108] cognitive factors of learning and attention [109][110][111][112], lesion of the peripheral or central nervous system [113,114] and direct micro-stimulation in the absence of peripheral stimulation [115]. It is notable that Belci et al [105] observed reductions in cSP and improvements in somatic percepts, effects that may be attributed to direct stimulation of the primary somatosensory cortex.…”