Background: Cortical reorganization has been shown to occur in the adult central nervous system. Plasticity contributes to various forms of human behavior including learning and memory, different forms of short and long term retention and skill acquisition. Understanding of the role of these different processes in human behavior and of the mechanisms underlying these various forms of human plasticity in the healthy central nervous system represents an important scientific problem. ? Findings this year: This year, we developed new techniques to modulate motor learning using transcranial DC stimulation (tDCS) and transcranial magnetic stimulation (TMS), we identified neural substrates underlying transfer of procedural motor learning, which included the supplementary motor areas. This work is presently in press in Current Biology. We identified advantages of the use of tDCS to design improved placebo experimental designs. We developed a novel tool to study fMRI in parametric motor tasks for upper and lower extremities. We characterized levodopa increases in memory encoding and dopamine release in the striatum in the elderly. We advanced in identifying the role of voluntary drive in encoding an elementary motor memory in the primary motor cortex, as well as identified plastic changes in the human H reflex and other intraspinal circuits at rest following skillful cycling training. A particular effort focused on the understanding of the role of interhemispheric inhibition in motor function and skill acquisition. We found well defined intermanual differences in movement-related interhemispheric inhibition as well as differences between proximal and distal hand muscles and also advanced our understanding of the neurophysiological mechanisms involved in transfer of procedural knowledge. One of the most important findings related to the understanding of the functional influences of unilateral hand training on cortical reorganization within the ipsilateral motor cortex.? Our future plans include advancing our understanding of the mechanisms underlying the effects of brain stimulation on motor learning and memory formation in the healthy brain. Additionally, we plan to gain understanding on the brain regions that contribute to two fundamental behavioral processes engaged in motor learning: intermanual transfer of procedural motor learning and the process of generalization of skill acquisition. That is, the mechanisms by which learning to perform one task with one hand allow humans to improve performance of different unrelated tasks.? Implications: These studies will improve our understanding of the mechanisms underlying human learning and memory processes, and by gaining this understanding, will allow us to develop more effective interventions to modulate them when necessary using brain stimulation.
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