Sleep's impact on emotional recognition memory: A meta-analysis of whole-night, nap, and REM sleep effects

Numerous studies have shown that post-learning sleep enhances visual episodic recognition memory. However, it remains unclear whether this consolidation benefit is moderated by the emotional valence of the learned material. To clarify whether sleep selectively enhances memory for emotional material, we conducted a meta-analysis including N = 1059 post-sleep/wake observations. Overall, our results do not support this hypothesis. When only studies with a sleep group/wake group comparison were included in the analysis (k = 22), the retention advantage for emotional (negative/positive) over neutral material was not significantly different between sleep and wake groups. When studies without wake groups were included in the analysis after statistical estimation of wake–group parameters, the retention advantage for emotional material was significantly larger in wake groups than in sleep groups (k = 34). Interestingly, however, an additional analysis of eight studies investigating the selective effects of rapid-eye-movement sleep and slow-wave sleep on post-interval emotional memory provided evidence for a selective enhancement of emotional over neutral memory performance after rapid-eye-movement sleep compared to slow-wave sleep. These findings suggest that sleep does not generally enhance visual recognition memory for emotional stimuli. However, the result pattern is consistent with the idea that specific sleep stages preferentially enhance consolidation of emotional and neutral material, respectively.