SENSORIMOTOR CORTEX IN PROSIMIAN PRIMATE

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The long-term objective of these multidisciplinary studies of the structure and function of the somatic sensory system in the prosimian primate, Galago, is to understand how the primary (SI) and secondary (SII) projection areas in the cerebral cortex contribute to the capacity to discriminate tactile stimuli with the hand. Recent behavioral, physiological and anatomical studies of infant and adult Galago, and Macaca, have led to a variety of questions about parallel vs. serial sensory processing in the somatic sensory system in primates. Our recent physiological studies on Galago have provided a detailed map of the hand and body in SII and a complete body map in SI. Our on-going neuroquantatative studies, using the new texture stimulator we developed, are examining the differences in response properties between and SII neurons. In behavioral studies we have established the level of normative tactile capacity of adult Galago, as compared to Macaca and New World monkeys, and measured the behavioral deficits associated with SI and SII removals in adult Galago. Preliminary studies of Sl and SII lesions in infant Galago (in agreement with our studies of infant Macaca) show recovery or sparing after tactile damage after SI or SII damage. Our anatomical studies of adult Galago have shown a pattern independent thalamic projections to SI and SII in adults but our recent studies find pattern of overlapping axon collaterals to SI and SII in infant Galago. Based on these recent findings the proposed research is designed to demonstrate recovery (or sparing) of tactile function after Sl and SII lesions in infants, to examine the patterns of thalamocortical connections in the infant and adult, and to investigate how maintenance of normally-transient collaterals may provide the neural basis for normal tactile function following lesions in infant primates. The Galago provides an ideal preparation for these studies given our knowledge of the simple cortical organization and thalamocortical connections in the adult and the rapid development infants in this primate species. We expect that studies of Galago at different ages may show: 1) a greater recovery of tactile function in the infant than in the adult animal; 2) abundant collaterals of thalamic projections to BI and SII in normal infants but not adults; 3) maintenance of transient thalamocortical axons in the SI- or SII-lesioned, but not the normal, infant that may provide the mechanism for recovery or sparing of function following brain damage in the infant primate.