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 [ [1] , [2] , [3] and [4] ]. 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 [ [5] and [6] ]. 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 [3]. 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 (>30 Hz) [ [7] , [8] , [9] and [10] ]; a candidate factor contributing to hyperarousal and exaggerated amygdala reactivity [3 M.P. Walker and E. van der Helm, Overnight therapy? The role of sleep in emotional brain processing. Psychol. Bull., 135 (2009), pp. 731–748. Article | PDF (557 K) | | View Record in Scopus | | Full Text via CrossRef | Cited By in Scopus (30) [3] , [11] , [12] and [13] ]. 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.