STATIC AND DYNAMIC ORGANIZATION

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The proposed experiments have two goals: First, to investigate the normal functional organization of motor cortex in adult primates and second, to explore the capacity of motor cortex representations to reorganize following peripheral nerve injury or subsequent to the acquisition of a skilled movement. MI representation pattern will be evaluated by combining intracortical microstimulation mapping with EMG recording techniques and by using extracellular and intracellular tracing techniques. Normal "static" MI organization pattern: Unlike previous studies that have described the movements evoked by MI stimulation, our studies will demonstrate the representation of functional groups of forelimb muscles in MI by recording EMG activity from each of 16 muscles that are activated from individual cortical sites. Muscle representation will be mapped at 100-200 MI sites using several different current intensities. These data will be used to determine the topological relationship, extent of overlap, and size of representation of each of the 16 muscles. Our preliminary data suggest that some muscles are multiply represented in spatially separate foci that overlap the representation of several other muscles. These foci may represent a pattern of functional grouping that has been described in MI. Intracellular recording/dye injection and anatomical pathway tracing techniques will be used after mapping to examine the connectional relationship between these individual or grouped representations in MI. Dynamic organization: A second goal of these studies is to determine the extent to which the relationship of the motor cortex with the muscles is changed (a) under normal conditions (i.e., is there a continual reshaping of MI representations?), (b) following nerve injury that prevents the normal use of the distal forelimb muscles, (c) following the acquisition of skilled digit movements. Microstimulation mapping will be used to study MI representation patterns at different intervals in normal animals, before and after anterior interosseus nerve section and before and after learning of a precision finger grip task. These experiments will provide important new information concerning the efferent topography of primate motor cortex as well as the flexibility of the relationship between MI cortex and muscles. The results of these studies may suggest new strategies for enhancing functional recovery and suppressing spasticity subsequent to injury of the peripheral and central nervous system.