We have identified a new pattern of input-output organization for the primate motor cortex. Namely, the primary motor cortex contains 2 spatially separate representations of the hand. One representation is located in the caudal part of area 4 and receives somatosensory afferent input largely from cutaneous receptors on the volar surface of the hand. The second representation is located in the rostral part of area 4 and receives input largely from muscle and/or joint receptors located in the distal forelimb. Based on these and other observations we have proposed that the 2 hand representations represent 2 motor control systems in area 4 which may independently control different aspects of motor behavior. Furthermore, we have suggested that these systems may have been anatomically separated to facilitate differential control over their inputs and/or outputs. We believe that further important insights into the functional significance of the 2 hand representations in primary motor cortex will come from a more complete understanding of their connectivity. Thus, the primary objective of the experiments is to define the input-output organization of the 2 hand representations using combined anatomical and physiological methods. This objective will be accomplished in 4 Specific Aims: I. Define the organization of inputs to the rostral and caudal zones of hand representation in the primary motor cortex. II. Investigate the topographic organization of cortico-cortical neurons in the primary motor cortex. III. Define the organization of inputs to the rostral and caudal zones of distal hindlimb representation in the primary motor cortex. IV. Define the organization of corticospinal projections from the rostral and caudal zones of hand representation in the primary motor cortex to the cervical segments of the spinal cord. The goal of our studies is to understand how the 2 hand representations in primary motor cortex contribute to the suprasegmental generation and control of movement. The results of the studies should provide the anatomical framework necessary for achieving our long term goal.
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