Functional Organization of the Somatosensory System

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DESCRIPTION (provided by applicant): The broad objectives of this research program are to determine the normal organization of sensory and motor systems in primates, how these systems process sensory information, and how they respond to damage. Aim 1. We will use microelectrode recordings to identify representations of the teeth and tongue in area 31, 3b, and 1 of monkey somatosensory cortex, place injections of tracers in these representations, and reveal much of the cortical network for processing information from these structures. This network is only partly known, and yet proper food evaluation and processing are critically important to human health. Aim 2. Microstimulation experiments in posterior parietal cortex suggest that this cortex contains a number of distinct subregions where different ethologically relevant movement patterns can be evoked. We will use microstimulation to define these regions in monkeys, and inject tracers into these regions and presumptive targets to determine their connections with higher order sensory areas and to motor and premotor areas in monkeys. An understanding of this system would promote an understanding of how such regions function and malfunction in humans. Aim 3. We will use chronically embedded microelectrode arrays to intensively study the response properties of neurons in somatosensory hand cortex (3a, 3b, 1) of monkeys, with an emphasis on the interactions of effects of stimuli within and outside the minimal receptive field. The results will reveal contextual effects that are at the roots of form and object perception, and highly relevant to somatosensory processing in humans. Aim 4. The integrity and plasticity of somatosensory and motor representations will be evaluated with microelectrode recordings and microstimulation after recoveries from high cervical dorsal column lesions in the spinal cords of neonatal and mature monkeys. Chronically embedded electrode arrays in somatosensory cortex will evaluate the response properties of reactivated neurons. Injections of tracers into motor cortex will reveal any alterations in corticospinal projection patterns. Microstimulation experiments will reveal possible alterations in the functional organization of motor cortex as a result of sensory deprivation. These experiments will reveal the types of reorganization that occur in mature and developing systems after massive sensory loss. Results may lead to more effective post-injury treatments for humans with spinal cord injury.