Does REM sleep help us remember upsetting events without making them feel less upsetting?

Details

Emotion boosts the consolidation of events in declarative memory. Rapid eye movement (REM) sleep is believed to support the consolidation of emotional events, while also being assumed to reduce the emotional tone of those memories.

This experimental study compared selective REM-sleep deprivation, slow-wave sleep (SWS) deprivation, and wakefulness to investigate their effects on memory consolidation and the affective evaluation of emotional and neutral pictures. Before a 9-hour retention interval, 62 healthy participants (age 23.5 ± 2.5 years; 32 female, 30 male) learned 80 neutral and 80 emotionally negative pictures and rated their emotional responses to them.

Despite rigorous deprivation of REM sleep or SWS, the remaining sleep supported the consolidation of both neutral and negative pictures. Emotional arousal also helped participants remember the pictures. The advantage in consolidation for negative over neutral pictures was most pronounced in the SWS-deprived group, which had a normal amount of REM sleep. This emotional memory bias correlated with REM sleep only in the SWS-deprived group.

Emotional arousal in response to the pictures decreased over time, but sleep and wakefulness did not have different effects on this decrease. Neither comparisons of affective ratings—arousal and valence—during encoding and recognition, nor affective ratings of correctly recognized target pictures and correctly rejected distractor pictures supported the hypothesis that REM sleep dampens emotional reactions to remembered stimuli.

The data suggest that REM sleep supports the consolidation of emotional memories but has no effect on the affective evaluation of their remembered contents.