FUNCTIONAL ORGANIZATION OF THE SOMATOSENSORY SYSTEM

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The proposed integrative, systems level somatosensory research addresses three major goals. 1) We will determine how the developing and mature somatosensory systems of primates reorganize after major losses of sensory afferents. In a preliminary study, we demonstrated that dorsal column lesions in monkeys result in a moderate to massive reorganization of somatosensory cortex. In a series of new experiments, branches of peripheral nerve afferents will be cut as they rise in the dorsal columns of the spinal cord, and reorganizations and mechanisms of reorganization will be studied at cortical and subcortical levels after complete or incomplete removals of hand afferents. Lesions in newborns are expected to lead to more extensive and possibly different recoveries. Partial sections are expected to lead to more rapid and more functional recoveries. Evaluation processing include state-of-the-art multisite recordings from chronically implanted microelectrodes. 2) Related experiments will investigate cortical organization after partial or complete lesions of hand cortex in area 3b. For both types of studies, the response properties of altered neurons, and behavioral impairments and recoveries will be evaluated. The roles of the growth of new connections and histochemical changes in recovery will also be studied. 3) We plan to advance our basic understanding of the functional organization of the somatosensory system of primates by determining the connections of two areas of somatosensory cortex, discovered in our laboratory, PV and VS, and compare these connections with those of other areas in the same animals. In addition, we will compare the chemorchitecture of somatosensory and motor cortex in monkeys, chimpanzees, and humans to help identify valid subdivisions of cortex in humans and reveal human specialization. These three types of studies will provide a) an understanding of the scope and mechanisms of plasticity in the developing and mature somatosensory system that can guide programs of therapy in humans, and b) a more detailed and comprehensive understanding of the organization of the somatosensory system in primates that is especially relevant to humans and as a guide for future research.