Recent findings suggest that sleep might serve a role in emotional coping. In the study by Lucia M. Talamini, Laura F. Bringmann and others, the impact of an emotionally distressing experience on the sleep was assessed through EEG correlates. The experimental set up involved presentation of an emotionally neutral or distressing film fragment in the evening, followed by polysomnographic* registration of undisturbed, whole-night sleep and assessment of emotional reactivity to film cues on the next evening. Researchers found that emotional distress induced mild sleep deterioration, but also an increase in the proportion of slow wave sleep, and altered patterning of rapid eye movement sleep (REM).
While REM sleep occurrence normally increases over the course of the night, emotional distress flattened this distribution, accompanied by reduced REM latency and increased early night REM sleep, and correlated with an increased number of REM periods. Importantly, two subpopulations have been discerned, based on a subjective sleep quality following the emotional stressor: one subpopulation showed a moderate emotional response to the distressing stimulus and responded with elevated slow wave sleep (SWS) percentage and increased sleep quality during the subsequent night; the other showed a stronger emotional response to the distressing stimulus and responded with flattening of the REM sleep increase over the night and lowered sleep quality.
Previous studies related SWS to the purpose of the ‘replay’ and consolidation of memory representations. As the current study shows, the slow wave sleep increase is also an adaptive response to emotional distress: favorable SWS traits may protect against persistence of emotional distress. On the other hand, and perhaps not surprisingly, increased sleep disruptions (awakenings) after emotional distress were related to poor emotional dissipation over sleep.
The REM shifts towards sleep onset may relate to an increased urgency for REM-related reprocessing of distressing event memories. Such notions are generally in line with other studies implicating REM sleep and dreaming in reprocessing of distressing information. However, there wasn’t found any support for a relation between emotion-induced REM alterations and overnight emotional dissipation. This might reflect that REM sleep repatterning is not consistently related to emotional dissipation, at least not on the short term.
The research discovery of subpopulations with differential sleep and emotional characteristics associates a coupling of certain emotion and sleep traits with distinct emotional sleep types. This means some people may be more able to cope with emotionally distressing experience than others, depending, to notable extent, on sleep traits.
What does it mean for the dreams people have during the night? Although most dreams do take place during REM sleep, other recent research has shown that dreams can occur during any of the sleep stages. Most NREM dreams, however, don't have the intensity of REM dreams. This leads to the conclusion – people tend to see less vivid dreams after emotionally distressing experience.
*Polysomnography, also called a sleep study, is a test used to diagnose sleep disorders. Polysomnography records brain waves, the oxygen level in blood, heart rate and breathing, as well as eye and leg movements during the study.