The idea that the body representation in the SI cortex is a composite of multiple, somatotopically organized regions is widely accepted by workers in the forelimb regions of cat area 3b and monkey area 1 are mosaics comprised of discrete columnar units, called """"""""segregates"""""""". Three attributes characterize these mosiacs: (1) every site within a segregate receives its strongest peripheral input from the same skin locus; (2) neighboring segregates are separated from each other by sharp boundaries; and (3) adjacent segregates receive their strongest inputs from discrete, non-overlapping skin loci.
The aim of the present study is to determine if segregates exist in the orofacial region of SI of the squirrel monkey. The """"""""minimal"""""""" receptive field (minRF), defined as the skin area from which a near-threshold punctate stimulus evokes the strongest response for a neuron cluster in the anesthetized animal, will be used to estimate the skin area providing the strongest input to each recorded neuron cluster. Two complimentary experimental approaches are proposed. In the first, minRFs will be sampled every 100 um during near-radial penetrations with the purpose of determining if SI orofacial region contains numerous discontinuities (abrupt shifts of minRFs). The second approach will use arrays of closely spaced penetrations to detect the existence of small nonoverlapping cortical columns characterized by 1) absence of minRF shift within such column, and 2) abrupt shifts of minRF at a boundary between adjacent columns. the demonstration of a segregate organization in the orofacial region of SI would have significant impact on current views of the topographic organization and the thalamic and cortical connectivity of this field. It would also impact on current views of the information processing mechanisms which occur within it. If segregates exist in the orofacial cortex, a more comprehensive study of the relationships between segregate organization and other dimensions of somatosensory cortical functional architecture will be initiated.
