Temporal proximity to sleep determines emotional memory interference.

Memory cues can be associated with both positive and negative experiences at different time points, in either a positive-to-negative or negative-to-positive order. While sleep preferentially consolidates recent experiences, its impact on emotional memory across such opposing-valence sequences remains unclear. We tested whether sleep differentially modulates delayed cue affect in positive-to-negative versus negative-to-positive conditions. One hundred twenty participants were randomly assigned to sleep or wake groups and completed both conditions in counterbalanced order. Participants learned pseudoword-picture associations where the same cues were paired with emotional pictures of opposite valence. Emotional valence ratings were collected immediately after encoding and after a 12 h interval (overnight sleep vs. daytime wakefulness). Sleep led to more positive cue ratings in the negative-to-positive condition and more negative ratings in the positive-to-negative condition, compared to wake controls. Stronger positive picture ratings predicted greater positive-valence shifts after sleep in the negative-to-positive condition. These findings indicate that sleep preferentially modulates the affective tone of memories encoded closer to sleep onset, independent of recognition accuracy. This suggests a dissociation between mnemonic and affective consolidation, where sleep selectively biases emotional value according to the temporal order of experience. This principle may inform therapeutic strategies for optimizing emotional outcomes by timing positive experiences before sleep, though clinical applications require further study.