FINGER VS ELBOW TRACKING: COMPETITION FOR CORTICAL REPRESENTATIONS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Neuroplastic changes in the brain include enduring reorganization (Boroojerdi et al., 2001) attributable to the dynamic circuitry of the cortex (Sanes and Donoghue, 2000). Rehabilitation research involving individuals with neurological impairments, especially stroke, is placing greater emphasis on training paradigms promoting such changes in the brain (Carey et al., 2002; Carey et al., 2004; Gow et al., 2004; Koski et al., 2004; Liepert et al., 2000). However, understanding of the mechanisms of reorganization following rehabilitation is still far from complete. Complex skill acquisition or skill re-learning can promote neuroplastic representational changes at the level of the motor cortex, often referred to as the "learning-dependent hypothesis" (Kleim et al., 1998; Plautz et al., 2000). Plautz et al. (2000) evaluated this hypothesis by training squirrel monkeys on either a complex, small-well pellet retrieval task or on a simple, large-well pellet retrieval task respectively. The small-well task required skilled digit use that led to greater efficiency of pellet-retrieval in the small-well group. This was paralleled by expansion in distal forelimb (digit) cortical representational area with reduction in proximal (wrist/forearm) representation. The large-well group animals executed repetitive, unskilled activity and failed to demonstrate any changes in cortical maps. Thus, learning of a skill is the key element in triggering reorganization. However, it has not been addressed whether the expansion of distal movement representations was accompanied by deterioration in performance of the movement representations that suffered a contraction, viz. wrist/forearm. As more and more emphasis is being laid on motor learning based paradigms in treatment of individuals with lesions of the CNS, it is becoming increasingly important to know whether favorable expansion of representations associated with functional improvements for a segment (e.g. hand) following rehabilitation, induces deleterious effects on function at untrained segments that suffer a reduction in representation (e.g. elbow).