The dynamics of emotional behaviors in rapid eye movement sleep.

Dream's emotions could exert a major role in desensitizing negative emotions. Studying emotional dynamics (how emotions fluctuate across time) during rapid eye movement (REM) sleep could provide some insight into this function. However, studies so far have been limited to dream reports. To bypass this limit, REM sleep behavior disorder (RBD), in which participants enact their dreams, enables direct access to overt emotional dream behaviors (such as facial expressions and speeches). In total, 17 participants with RBD, and 39.7 h of REM sleep video were analyzed. The frequency of emotional behaviors did not differ between REM sleep episodes of early and late night. Within individual REM sleep episodes, emotional behaviors exhibited a biphasic temporal course, including an increased frequency for the first 10 min, followed by a progressive decrease. The negative emotional behaviors occurred earlier (mean time: 11.3 ± 10 min) than positive (14.4 ± 10.7 min) and neutral behaviors (16.4 ± 11.8 min). Emotional behaviors of opposing (negative and positive) valences were observed in 31% (N = 14) of episodes containing at least one emotional behavior, and were separated by a median time of 4.2 [1.1-10.9] min. The biphasic temporal course of behaviors in REM sleep could include the generation reactivation of emotional content during the ascending phase, followed by processing and extinction during the descending phase. The earlier occurrence time of negative emotional behavior suggests that negative emotions may need to be processed first. The rapid succession of emotions of opposite valence could prevent prolonged periods of negative emotions and eventually nightmares.