REM sleep chills out amygdala, reduces emotional reactivity

van der Helm et al. at Univ. of Cal. Berkeley have done interesting experiments in which 34 adults were randomly assigned to two groups which both performed an emotion reactivity test twice inside a functional magnetic resonance imaging (fMRI) scanner; separated by a 12 hr interval. The tests involved the rating and subsequent rerating of the same standard set of 150 affective picture stimuli. One group slept during the twelve hours interval with REM (rapid eye movement) sleep monitored by EEG, the other group was a control group that stayed awake during the day. Controls were done to eliminate possible time-of-day differences in emotional reactivity, independent of wake or sleep. Here is their abstract:

Clinical evidence suggests a potentially causal interaction between sleep and affective brain function; nearly all mood disorders display co-occurring sleep abnormalities, commonly involving rapid-eye movement (REM) sleep. Building on this clinical evidence, recent neurobiological frameworks have hypothesized a benefit of REM sleep in palliatively decreasing next-day brain reactivity to recent waking emotional experiences. Specifically, the marked suppression of central adrenergic neurotransmitters during REM (commonly implicated in arousal and stress), coupled with activation in amygdala-hippocampal networks that encode salient events, is proposed to (re)process and depotentiate previous affective experiences, decreasing their emotional intensity. In contrast, the failure of such adrenergic reduction during REM sleep has been described in anxiety disorders, indexed by persistent high-frequency electroencephalographic (EEG) activity (greater than 30 Hz); a candidate factor contributing to hyperarousal and exaggerated amygdala reactivity. Despite these neurobiological frameworks, and their predictions, the proposed benefit of REM sleep physiology in depotentiating neural and behavioral responsivity to prior emotional events remains unknown. Here, we demonstrate that REM sleep physiology is associated with an overnight dissipation of amygdala activity in response to previous emotional experiences, altering functional connectivity and reducing next-day subjective emotionality.