This project is designed to determine the role of the cerebral cortex in the sensory function of the primate hand. Neurophysiological and psychophysical techniques will be used to examine how the somatosensory system integrates spatial information on the skin. The contribution of phasic mechanoreceptors in the hand (Pacinian and Meissner's corpuscles) to cortical processing of motion, texture, size, shape and orientation of tactile stimuli will be studies using a computer controlled OPTACON stimulator which normally serves as a reading aid for the blind. Single unit recordings made in SI (areas 3b, 1 and 2), posterior parietal (areas 5 and 7b), and SII cortex of alert monkeys should reveal the contributions of each cytoarchitectural area to the analysis of spatial patterns such as stripes, geometric forms and alphanumeric characters, Studies of multiples ares in the same animal's brain will provide important information concerning the role of serial and parallel processing in the cerebral cortex for feature analysis. Experimental animals will also be trained using operant behavioral techniques and positive reinforcement to discriminate features such as direction of motion, bar width and orientation, as well as pattern shape in order to relate the information coded by cortical neurons to actual sensory perception in the same animal. Parallel psychophysical experiments in humans will allow correlation of sensations produced by the stimulus in humans and monkeys. Specific problems addressed by these experiments include: (1) How do cortical neurons integrate stimulus motion across gaps on the fingers? (2) What cortical mechanisms are sued to resolve the distance between stripes in a texture pattern? (3) HOw do cortical cells code the width, length and orientation of bar patterns scanned across the hand or fingers? (4) How do the total number of mechanoreceptors activated, and the area of stimulation on the skin, modify cortical responses? (5) How do neurons with multidigit receptive fields integrate spatial information? (6) How does motion affect orientation selectivity? (7) What are the roles of serial and parallel channels for tactile information processing in the cerebral cortex? (8) How does behavioral relevance of tactile stimuli modify cortical representation of form, orientation and direction of motion? These studies will provide important neurophysiological data on the tactile information processing capabilities of the cerebral cortex, the functional organization of five different cytoarchitectural areas, and the integration of information between the two hemispheres. The findings may have important clinical applications such as the development of more quantitative tests of sensory function in patients with neurological disorders or peripheral nerve injuries, and the improvement of sensory substitution aids for visually and/or hearing impaired individuals.
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