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

Shaping the structural dynamics of motor learning through cueing during sleep

Enhancing the retention of recent memory traces through sleep reactivation is possible via Targeted memory reactivation (TMR), involving cueing learned material during posttraining sleep. Evidence indicates detectable short-term microstructural changes in the brain within an hour after motor sequence learning, and posttraining sleep is believed to contribute to the consolidation of these motor memories, potentially leading to enduring microstructural changes. In this study, we explored how TMR during posttraining sleep affects performance gains and delayed microstructural remodeling, using both standard diffusion tensor imaging and advanced neurite orientation dispersion and density imaging. Sixty healthy young adults participated in a 5 days protocol, undergoing five diffusion-weighted imaging sessions, pre- and post-two motor sequence training sessions, and after a posttraining night of either regular sleep (RS) or TMR. Results demonstrated rapid skill acquisition on day 1, followed by performance stabilization on day 2, and improvement on day 5, in both RS and TMR groups. (Re)training induced widespread microstructural changes in motor-related areas, initially involving the hippocampus, followed by a delayed engagement of the caudate nucleus. Mean Diffusivity changes were accompanied by increased neurite density index in the putamen, suggesting increased neurite density, while free water fraction reduction indicated glial reorganization. TMR-related structural differences emerged in the dorsolateral prefrontal cortex on day 2 and the right cuneus on day 5, suggesting unique sleep TMR-related neural reorganization patterns. Persistence of practice-related structural changes, although moderated over time, suggests a lasting neural network reorganization, partially mediated by sleep TMR.

Motor learning- and consolidation-related resting state fast and slow brain dynamics across wake and sleep

Motor skills dynamically evolve during practice and after training. Using magnetoencephalography, we investigated the neural dynamics underpinning motor learning and its consolidation in relation to sleep during resting-state periods after the end of learning (boost window, within 30 min) and at delayed time scales (silent 4 h and next day 24 h windows) with intermediate daytime sleep or wakefulness. Resting-state neural dynamics were investigated at fast (sub-second) and slower (supra-second) timescales using Hidden Markov modelling (HMM) and functional connectivity (FC), respectively, and their relationship to motor performance. HMM results show that fast dynamic activities in a Temporal/Sensorimotor state network predict individual motor performance, suggesting a trait-like association between rapidly recurrent neural patterns and motor behaviour. Short, post-training task re-exposure modulated neural network characteristics during the boost but not the silent window. Re-exposure-related induction effects were observed on the next day, to a lesser extent than during the boost window. Daytime naps did not modulate memory consolidation at the behavioural and neural levels. These results emphasise the critical role of the transient boost window in motor learning and memory consolidation and provide further insights into the relationship between the multiscale neural dynamics of brain networks, motor learning, and consolidation.