Microstructural dynamics of motor learning and sleep-dependent consolidation: a diffusion imaging study

Diffusion-weighted magnetic resonance imaging (DWI) allows the observation of (micro)structural brain remodelling in cortical and subcortical regions after time-limited motor learning. Post-learning sleep consolidation should lead to long-term microstructural brain changes, but concrete evidence remains limited. Here, we used both conventional diffusion tensor imaging (DTI) and Neurite Orientation Dispersion & Density Imaging (NODDI), that estimates dendritic and axonal complexity in white and grey matter, to investigate the microstructural brain mechanisms underlying time- and sleep-dependent motor memory consolidation. Sixty-one young healthy adults underwent 2 DWI sessions, with sequential motor training in between, on day 1 followed by the experimental night of total sleep deprivation or regular sleep. After 3 recovery nights at home, they underwent 2 further DWI sessions separated by a motor retraining session. Sequential motor learning resulted in immediate modifications in structural parameters in occipitoparietal and temporal regions, as well as in subcortical regions of interest. Similar changes were observed following relearning but at a smaller magnitude. Regarding delayed consolidation effects, learning-related changes only partially persisted 3 days after initial learning, and no post-learning sleep effect was detected. Our results show rapid motor learning-related remodelling, reflecting temporary processes in learning-related neuronal brain plasticity. Post-learning sleep-related cellular changes remain to be evidenced, possibly using more sophisticated brain imaging measures and spanning more extended timescales to allow the expression of structural changes.