Sleep Spindle-Locked Targeted Memory Reactivation Enhances Declarative Memory Consolidation
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Study Objectives
Sleep spindles are implicated in memory consolidation. Yet direct evidence linking spindle dynamics to declarative memory outcomes remains limited. We thus tested whether targeted memory reactivation (TMR) time-locked to sleep spindles enhances declarative memory, and whether the temporal organization of stimulated spindles–trains versus isolated events–is selectively associated with distinct memory outcomes.
Methods
Twenty-eight healthy young adults learned image locations from two categories (animals, clothing) in a grid, each paired with a distinct auditory cue. During overnight NREM sleep, one cue was replayed time-locked to spindles detected in real-time using a closed-loop system (TMR condition); the other served as the non-reactivated control (No-TMR condition). Category-cue assignment was counterbalanced. Post-sleep recall, recognition accuracy, and movement time were assessed.
Results
Recall accuracy was significantly higher in the TMR than the No-TMR condition (93.96% vs. 90.61%, p = .024), whereas recognition accuracy ( p = .139) and movement time ( p = .651) did not differ. Stimulation intensity within spindle trains correlated with the TMR effect on recall (Spearman ρ = .531, p = .004), whereas the proportion of isolated spindle stimulations correlated with the TMR effect on recognition (ρ = .563, p = .002). Cross-associations were not significant.
Conclusions
Spindle-locked TMR enhances recall-based declarative memory retention. The selective association between spindle temporal clustering and memory outcomes suggests that train-embedded and isolated spindles support different aspects of memory consolidation, highlighting spindle temporal context as a functionally relevant dimension of sleep-dependent memory processing.
