Somatosensory Cortex and Thalamus

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DESCRIPTION (provided by applicant): While area 5 has been considered a posterior parietal field involved exclusively in processing somatic inputs, recent evidence from our laboratory in both New World and Old World monkeys, as well as work from other laboratories, indicate that this cortical area is also involved in processing visual inputs, and is closely associated with the motor system. Accumulating evidence indicates that area 5 may be a "central planner" critical for monitoring limb location during intended reaching and grasping, converting sensory locations into motor coordinates for intentional movement, and in perceiving the movements of the body in extra personal space. The goal of the present investigation is to determine the role of posterior parietal area 5 in visually guided and non-visually guided reaching and grasping, object manipulation, bilateral coordination of the hands, and information transfer across the' cerebral hemispheres. To accomplish this, we will make electrophysiologically targeted unilateral lesions in the hand and forearm representation of area 5 in macaque monkeys, and examine the effects of these lesions on these behaviors. We expect that ablations of area 5 will result in a variety of deficits involving manual dexterity, reaching, grasping, and bilateral coordination of the hands. The proposed studies are broken into three major groups of experiments. The first series of experiments will examine the cortical, callosal, and subcortical connections of area 5 and adjacent somatosensory area 2, in macaque monkeys. The second group of experiments will examine the consequences of precisely targeted lesions in area 5 on directed reaching and grasping, bilateral coordination of the hands, shape discrimination abilities and interhemispheric transfer. The tasks include reaching and grasping under visually guided and non-visually guided conditions, bilateral manipulation of objects, and object identification under both ipsilateral and bilateral hand use conditions. The final series of experiments will examine the cortical substrate for behavioral recovery by determining if changes in both functional organization and anatomical cortical connectivity have occurred in cortical area 2 as a consequence of the lesion. This study represents one of the first attempts to combine modern neuroanatomical, electrophysiological, and lesioning techniques to determine the contribution of a single cortical field involved in generating sophisticated hand use. Further, it is one of the few studies that utilizes electrophysiological and neuroanatomical techniques to examine the long-term cortical changes that occur after cortical damage, followed by behavioral training. These studies will ultimately allow us to better understand the role of area 5 in reaching, grasping, object manipulation, and bilateral coordination of the hands, the time course of behavioral plasticity following lesions in area 5, and the cortical mechanisms that contribute to recovery after brain injury.