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), work published this year in PNAS, and transcranial magnetic stimulation (TMS), we identified neural substrates underlying transfer of procedural motor learning, which included the supplementary motor areas. This work has been published in Current Biology. We identified the ability of tDCS to improve spatial tactile acuity and specific activity dependent changes in the primary motor cortex ipsilateral to a moving hand. We identified an interesting set of interactions that are evidenced during observation of touch. We advanced our understanding of the contribution of the supplementary motor area to successful intermanual transfer of procedural motor learning. We also extended our studies of the role of the primary motor cortex on intermanual transfer of procedural motor learning to learning of force generation. In relation to the influence of brain stimulation, we found out a striking effect of stimulation of the primary motor cortex on performance of skilled motor tasks in elderly subjects. An important finding in this review period has been the determination of the importance of EMG monitoring from muscle groups in both upper extremities during fMRI studies involving motor actions and improved understanding of the neural substrates of motor mirroring. 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 and elderly 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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