The goal of this project is to understand how single neurons as well as ensembles of interacting neurons in multiple motor cortical areas coordinate proximal and distal components in reach-to-grasp behavior. Although psychophysical research has determined that prehensile movements involve the coordination of hand transport and grasp preshaping, very little is known about the cortical involvement in coordinating reach and grasp. Most electrophysiological recordings have focused on characterizing the firing of single cortical neurons in relation to either reaching or grasping movements separately. We will determine: 1) how single neurons within dorsal premotor (PMd), ventral premotor (PMv;F5), and primary motor (MI) cortical areas encode both reach and grasp components by explicitly characterizing the encoding of reach-to-grasp coordination;2) whether there is a topographic organization of reach and grasp neurons within these three cortical areas;and 3) whether there are structured spatiotemporal patterns of spiking among simultaneously recorded neurons that mediate the coordination of reach-to-grasp. To accomplish this, high-density electrode arrays will be chronically implanted in MI, PMv, and PMd from which 100s of single units and local field potentials will be simultaneously recorded while monkeys reach for and grasp objects of different sizes, shapes, and orientations in different three-dimensional locations. A digital optical tracking system using a set of six infrared cameras will monitor the kinematics of the arm and hand during reach-to-grasp behavior. A set of statistical and mathematical methods will be employed to develop encoding models of reach-to-grasp that capture how single neuron spiking and neuronal ensemble activity participate in the coordination of hand transport and grip aperture kinematics. Decoding models will also be used to compare how well ensemble activity within MI, PMv, and PMd can reconstruct the reach and grasp kinematics. More complex reach-to-grasp movements involving obstacle avoidance and grasp of moving objects will be used to test whether these encoding and decoding models generalize to altered coordination patterns.
Coordinated reaching and grasping is a ubiquitous feature of human behavior that traces its evolutionary roots to primate foraging for food in arboreal environments and has allowed for the development of more complex actions including tool use and, ultimately, knowledge acquisition through direct contact. The proposed project will enhance our understanding of the cortical contribution to these coordinated behaviors which may lead to more effective rehabilitative treatments for motor disabled patients with cortical damage due to stroke or injury. This work also has direct relevance towards the development of a neuro-motor prosthesis by which spinal cord-damaged or ALS patients may be able to control grasp as well as transport components of artificial devices by activating ensembles of motor cortical neurons.
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