Distributed and gradual microstructure changes track the emergence of behavioural benefit from memory reactivation
Memory traces develop gradually and link to neural plasticity. Memory reactivation during sleep is crucial for consolidation, but its precise impact on plasticity and contribution to long-term memory storage remains unclear. We used multimodal diffusion-weighted imaging to track the location and timescale of microstructural changes following Targeted Memory Reactivation (TMR) of a motor task. This showed continuous microstructure plasticity in precuneus across 10 days post-TMR, paralleling the gradual development of behavioural benefit. Both early (0 - 24 h post-TMR) and late (24 h - 10 days post-TMR) microstructural changes in striatum and sensorimotor cortex were associated with the emergence of behavioural effects of TMR at day 20. Furthermore, the baseline microstructural architecture of sensorimotor cortex predicted TMR susceptibility. These findings demonstrate that repeated reactivation of memory traces during sleep engenders microstructural plasticity which continues days after the stimulation night and is associated with the emergence of memory benefits at the behavioural level.