Done that: short-term repetition related modulations of motor cortex activity as a stable signature for overnight motor memory consolidation

An almost universally accepted tacit expectation is that learning and memory consolidation processes must be reflected in the average brain activity in brain areas relevant to task performance. Motor cortex (M1) plasticity has been implicated in motor skill acquisition and its consolidation. Nevertheless, no consistent pattern of changes in the average signal, related to motor learning or motor memory consolidation following a single session of training, has emerged from imaging studies. Here we show that the pattern and magnitude of short-term brain activity modulations in response to task repetition, in M1, may provide a robust signature for effective motor memory consolidation processes. We studied participants during the paced performance of a finger-to-thumb opposition sequence (FOS), intensively trained a day earlier, and a similarly constructed untrained FOS. In addition to within-session "on-line" gains, most participants expressed delayed, consolidation-phase gains in the performance of the trained FOS. The execution of the trained FOS induced repetition enhancements in the contralateral M1 and bilaterally in the medial-temporal lobes, offsetting novelty-related repetition suppression effects. Moreover, the M1 modulations were positively correlated with the magnitude of each participant's overnight delayed gains but not with absolute performance levels. Our results suggest that short-term enhancements of brain signals upon task repetition reflect the effectiveness of overnight motor memory consolidation. We propose that procedural memory consolidation processes may affect the excitation-inhibition balance within cortical representations of the trained movements; this new balance is better reflected in repetition effects than in the average level of evoked neural activity.