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Organization of the hand area in the primary somatic sensory cortex (SmI) of the prosimian primate, Nycticebus coucang
Author(s) -
Carlson Mary,
Fitzpatrick Kathleen A.
Publication year - 1982
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902040307
Subject(s) - receptive field , biology , anatomy , cortex (anatomy) , neuroscience , prosimian , sensory system , primate , numerical digit , dorsum , extrastriate cortex , stimulation , visual cortex , lemur , arithmetic , mathematics
The topography of low‐threshold (LT) cutaneous input from the hand to SmI cortex of the prosimian primate Nycticebus coucang was mapped in detail by means of threshold receptive field techniques. The area of cortex responding to LT stimulation of the hand can be divided into three distinct subdivisions on the basis of physiological as well as cytoarchitectonic criteria. The rostral subdivision in the hand area (G1) responds to stimulation of the glabrous surface of the digits and hand. Within this field cells located rostrally have receptive fields located on the glabrous digit tips, while caudally located cells respond to stimulation of the proximal glabrous palm. Receptive fields in G1 are small in size and have low thresholds. G1 is coextensive with an area of cortex having the cytoarchitectonic features of koniocortex. The caudal region of the LT hand area consists of two subdivisions. Laterally, cells in this caudal region (H) respond to stimulation of the dorsal hairy digits and hand. Receptive fields on the dorsal hairy digits are found rostrally in this subdivision, while receptive fields on the dorsal hand and wrist are encountered caudally. Thus, the hand is projected serially across G1 and H. Within H, thresholds are similar to those in G1, but receptive fields are much larger in H than in G1. A second glabrous hand area (G2), is found in the medial part of the caudal region of the LT hand area. In G2 receptive fields on the glabrous ulnar digits are encountered rostrally, while more caudally cells respond to stimulation of the radial digits. Few glabrous palm fields were found in G2. Receptive field sizes and thresholds in G2 are quite similar to those in G1. Subdivisions H and G2 have the cytoarchitectonic characteristics of parakoniocortex. Although H and G2 are not distinguishable from one another, they can be easily separated from the more rostral koniocortex which contains the first glabrous hand area (G1). Thus, the SmI hand area of Nycticebus is unique among those of the other prosimian, Galago , thus far mapped in that two separate somatotopic projection patterns of the glabrous hand are present within the LT area. In this respect, Nycticebus more closely resembles simian species in which multiple LT hand areas are present in SmI in all forms which have been mapped. This is not to suggest that G2 in Nycticebus is either homologous to, or a precursor of, those multiple cutaneous areas reported for Old and New World simian species. Rather we suggest that the second glabrous projection in Nycticebus , and that of simian species, may have been achieved by the displacement of the dorsal hand projection occupying the architectonically distinct caudal SmI field in earlier prosimian species.