Background: Cortical reorganization occurs in the adult central nervous system. Plasticity contributes to various forms of human behavior including motor learning and memory formation, consolidation, reconsolidation and short and long term retention. It is very important to understand the role of these different behavioral processes and of the mechanisms underlying these various forms of human plasticity during skill acquisition. Findings this year: We found that connectivity in the frontostriatal-limbic network predicted interindividual variability in the rewarded but not in unrewarded learning. Prediction was strongest for long-term memory. Similar links between connectivity and reward-memory were absent in two control networks, a fronto-parieto-temporal language network and the dorsal attention network. The results indicate that baseline functional connectivity within the frontostriatal-limbic network successfully predicts long-term retention of rewarded learning. Importantly, the enhancing effects of reinforcement on skill acquisition depend on reinforcement schedules. In reference to brain stimulation, we found that application of tDCS during learned EEG-based self-regulation of brain oscillations above 9 Hz is feasible and safe, and might improve applicability of BMI systems. We also determined that application of weak electric currents of opposite polarities over the primary motor cortex differentially modulates learning SMR control, pointing to this primary cortical region as a common substrate for acquisition of physical motor skills and learning to control brain oscillatory activity. We described accurate reconstructed localization of dipolar sources and changes of brain oscillatory activity associated with motor actions in primary cortical brain regions undergoing transcranial electric stimulation. This new method allows for the first time direct measurement of the effects of non-invasive electrical brain stimulation on brain oscillatory activity and behavior. in relation to learning, we reported that sleep encodes different representations of memory than practice, and may mediate conversion of memories between declarative and procedural forms. Using a combination of behavioral, brain stimulation, and neuroimaging paradigms, we reported that noninvasive transcranial magnetic stimulation interference with a reactivated motor memory altered offline task-free corticostriatal interregional functional connectivity, reducing it compared to stimulation in which the reactivated memory was intact. Furthermore, the modulated functional connectivity predicted offline memory modification. This reduction in functional connectivity recovered after additional execution of the memorized task, and the interference did not affect control cerebellar-cortical functional connectivity. This demonstrates that intrinsic task-free offline brain activity can be modulated by noninvasive interaction with existing memories and strongly correlates with behavioral measurements of changes in memory strength. In relation to memory, we demonstrated that right lateral prefrontal cortex plays a causal role in strengthening of episodic memories through reconsolidation in humans. Reconsolidation may serve as an opportunity to modify existing memories with noninvasive stimulation of a critical brain region, an issue of fundamental importance for memory research and clinical applications
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