The role of REM sleep in the processing of emotional memories: evidence from behavior and event-related potentials.

Emotional memories are vividly remembered for the long-term. Rapid eye movement (REM) sleep has been repeatedly proposed to support the superior retention of emotional memories. However, its exact contribution and, specifically, whether its effect is mainly on the consolidation of the contents or the processing of the affective component of emotional memories is not clear. Here, we investigated the effects of sleep rich in slow wave sleep (SWS) or REM sleep on the consolidation of emotional pictures and the accompanying changes in affective tone, using event-related potentials (ERPs) together with subjective ratings of valence and arousal. Sixteen healthy, young men learned 50 negative and 50 neutral pictures before 3-h retention sleep intervals that were filled with either SWS-rich early or REM sleep-rich late nocturnal sleep. In accordance with our hypothesis, recognition was better for emotional pictures than neutral pictures after REM compared to SWS-rich sleep. This emotional enhancement after REM-rich sleep expressed itself in an increased late positive potential of the ERP over the frontal cortex 300-500 ms after stimulus onset for correctly classified old emotional pictures compared with new emotional and neutral pictures. Valence and arousal ratings of emotional pictures were not differentially affected by REM or SWS-rich sleep after learning. Our results corroborate that REM sleep contributes to the consolidation of emotional contents in memory, but suggest that the affective tone is preserved rather than reduced by the processing of emotional memories during REM sleep.