Updating memories of unwanted emotions during human sleep

Abstract

Post-learning sleep contributes to memory consolidation. Yet, it remains contentious whether sleep affords opportunities to modify or update emotional memories, such as those people would prefer to forget. Here we attempted to update memories during sleep using spoken positive emotional words paired with cues to recent memories for aversive events. Affect updating using positive words during human non-rapid-eye-movement (NREM) sleep, compared with using neutral words instead, reduced negative affect judgments in post-sleep tests, suggesting that the recalled events were perceived as less aversive. EEG analyses showed that emotional words modulated theta and spindle/sigma activity. Specifically, to the extent that theta power was larger for the positive word than for the following memory cue, participants judged the memory cues less negatively. Moreover, to the extent that sigma power was larger for the emotional word than for the following memory cue, participants showed higher forgetting of unwanted memories. Notably, when the onset of individual positive word coincided with the upstate of slow oscillations, a state characterized by increased cortical excitability during NREM sleep, affective updating was more successful. In sum, the affect content of memories was altered via strategic spoken words presentations during sleep, in association with theta power increases and slow-oscillation upstates. These findings offer novel possibilities for modifying unwanted memories during sleep, without requiring conscious confrontations with aversive memories that people would prefer to avoid.