This project analyzes the role of somatosensory neurons in the parietal lobe during performance of skilled prehension tasks.
It aims to understand how the hand acquires information about object size and shape through the senses of touch and vision, and uses it to guide the fingers in skilled tasks. Synchronous neurophysiological recordings from ensembles of neurons in S-I and posterior parietal cortex (PPC) and measurements of hand kinematics assess temporal relations between neural populations representing individual fingers at several stages of cortical networks. These experiments test the hypothesis that synchronization and/or coherence of firing between cortical regions involved in planning and implementation of skilled hand movements enable a match-to-sample mode of tactile information processing and error correction. A trained prehension task in which the hand grasps small objects measures how kinematic and haptic features are integrated in PPC and S-I by examining whether neurons representing the hand encode the object's intrinsic spatial properties and/or its extrinsic features. We propose that anticipatory precontact activity in PPC reflects motor planning needed to grasp objects efficiently and to secure them for manipulatory action. Post-contact responses in S-I are postulated to confirm or rebut the animal's expectation of haptic properties, rather than encode specific physical parameters, and to provide feedback information necessary for error correction. We also examine how actions of the two hands are coordinated during skilled actions using simultaneous bilateral recordings from left and right hemispheres. Hand-to-hand transfer, symmetric bimanual grasp and hand-mouth interaction during feeding are compared to unimanual actions to determine whether hand coordination result from temporal synchronies between hemispheres, and/or unilateral neuronal specialization for bimanual behaviors. Investigation of autonomous bilateral control is a prerequisite for understanding hemispheric specialization and unilateral dominance. These experiments will provide fundamental insights into the dynamic organization of cortical circuits, and the role of sequential hierarchical processing and parallel distributed processing in cortical function. The paradigms will help define the tactile information processing capabilities of the cortex, and the neural basis of stereognosis, a major neurological test of hand function. They provide important neurophysiological data on sensorimotor integration in hand function, the functional organization of different cytoarchitectural areas, and the temporal integration of spatial information within the cortex.
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