Targeted memory reactivation during sleep promotes more consistent neural dynamics

Targeted Memory Reactivation (TMR) during non-rapid eye movement (NREM) sleep is widely used to investigate memory reactivation and consolidation. Previous studies have identified electrophysiological signatures of TMR, including cue-evoked oscillatory responses and the reinstatement of learning-related neural representations. However, little is known about how memory reactivation influences the large-scale dynamical organization of brain activity during sleep. Here, we analyzed high-density EEG recordings from a previously published TMR study in which auditory cues associated with prior learning and acoustically matched control cues were presented during NREM sleep. Neural complexity was quantified using Sample Entropy (SampEn) across the full EEG spectrum and canonical frequency bands. We examined both mean entropy and entropy dispersion across cue presentations. Memory-associated cues produced a robust reduction in entropy dispersion, measured using both standard deviation and interquartile range, across all frequency bands. This effect was highly consistent across participants and remained evident at the individual level. In contrast, mean entropy did not differ between memory and control conditions. Likewise, relative spectral power analyses revealed no significant differences between conditions in any frequency band. These findings indicate that memory reactivation during sleep is associated with more consistent neural dynamics without altering overall neural complexity