Emotional memories are enhanced when reactivated in slow wave sleep, but impaired when reactivated in REM

Sleep supports memory consolidation. However, it is not completely clear how different sleep stages contribute to this process. While rapid eye movement sleep (REM) has been traditionally implicated in the processing of emotionally charged material, recent studies indicate a role for slow wave sleep (SWS) in strengthening the memories of emotional stimuli. Here, to directly examine which sleep stage is primarily involved in emotional memory consolidation, we used targeted memory reactivation (TMR) in REM and SWS during a daytime nap. We also examined neural oscillations associated with TMR-related changes in memory. Contrary to our hypothesis, reactivation of emotional stimuli during REM led to impaired memory. Meanwhile, reactivation of emotional stimuli in SWS improved memory and was strongly correlated with the product of times spent in REM and SWS (%SWS × %REM). When this variable was taken into account, reactivation significantly enhanced memory, with larger reactivation benefits compared to reactivation in REM. Notably, sleep spindle activity was modulated by emotional valence, and delta/theta activity was correlated with the memory benefit for both emotional and neutral items. Finally, we found no evidence that emotional memories benefited from TMR more than did neutral ones. Our results provide direct evidence for a complementary role of both REM and SWS in emotional memory consolidation, and suggest that REM may separately facilitate forgetting. In addition, our findings expand upon recent evidence indicating a link between sleep spindles and emotional processing. ### Competing Interest Statement The authors have declared no competing interest.