Our goal is to examine in human and non-human primates, the contribution of the somatosensory system to complex primate behaviors such as manual dexterity, bilateral coordination of the hands, multimodal integration, and sensorimotor integration required for goal directed reaching. The evolution of these abilities in humans is intertwined with the evolution of our sensory and motor systems. In order to understand how these sophisticated behaviors are generated, we must uncover the details of the organization of our sensory systems, and the neural circuitry that subserves complex functions. Studies of cortical fields in the lateral sulcus (LS; SII, PV, VS, 7b, and RL) indicate that they are involved in tactile discrimination, tactile recognition, attention, and integration of unilateral and bilateral inputs across the hands. Areas in posterior parietal cortex (PP; areas 5, 7a, LIP and VIP) are involved in generating motor coordinates for directed movements, attention, and multimodal integration. Our studies are aimed at uncovering the topographic organization of cortical fields, receptive field size, stimulus preference, and detailed topographic connection patterns of fields in LS and PP in monkeys, and determining if similar fields exist in humans. Our proposal combines several data collection techniques. In non-human primates we will record extracellularly from clusters of neurons in cortical fields in LS and PP in response to quantifiable, reproducible stimuli such as small indentations on the glabrous surface of the hand, displacement of hairs, light strokes along the glabrous surface of the hand in different directions, pressure, muscle manipulation, and digit, wrist and hand movements. In some of these same monkeys, the detailed patterns of intracortical, callosal, and thalamic connections will be determined by placing anatomical tracers into electrophysiologically defined subdivisions, and then mapping target structures using multiunit electrophysiological recording techniques. Recently, it has been established that the fMRI technique can be used effectively in humans to determine the topographic organization of fields, and the number of subdivisions within a region of cortex. In parallel with our electrophysiological and connection studies in monkeys, we will utilize fMRI techniques to explore similar regions of the neocortex in humans. Our stimulus selection and areas of interest will be guided by our results in monkeys. Thus, we will begin with stimulation like that described above, and direct our efforts to areas in the LS and PP cortex. Applying the framework of cortical fields and patterns of connections established in our monkey model to humans, we can expand our stimulus repertoire to include more sophisticated tasks which involve bilateral manipulation, goal directed reaching, and multimodal integration. This study represents one of the first efforts to combine results from human and non-human primate studies, and promises to provide a richer understanding of somatosensory cortex, and its contribution to higher perceptual and cognitive processing.
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