Sleep reactivation shapes memories of event and its temporal structure
Episodic memory provides a temporal scaffold that organizes past experiences according to their sequential occurrence. While memories are reactivated and consolidated during sleep, it remains unknown how exogenous reactivation reshapes memories of complex events, particularly the temporal structure that binds individual elements across time. In this preregistered study, 35 participants encoded neutral and aversive narratives composed of image sequences, with auditory context shifts defining event boundaries. During post-encoding slow-wave sleep, closed-loop targeted memory reactivation (TMR) delivered boundary-associated auditory cues time-locked to the up-state of slow oscillations. Reactivation led to faster, more confident, and more liberal recognition responses for cued than uncued memories. However, reactivation exerted a time-dependent effect on temporal-order memory, impairing it immediately after sleep but attenuating forgetting one week later. This behavioral dissociation was paralleled at the neural level: stronger cue-elicited theta activity predicted superior recognition of neutral, but not aversive event content, whereas greater theta responses were associated with poorer temporal-order memory for the same events. Together, these findings suggest that sleep reactivation does not uniformly strengthen episodic memories. Rather, it selectively prioritizes access to event content while reorganizing temporal relations among event elements, revealing distinct, time-dependent consequences of sleep reactivation for different components of complex experiences.