REM sleep is still a mystery. A great amount of evidence is suggesting a link between this stage of sleep and the processing of memory/emotion.
Interesting data, but still I wonder if this is an effect of sleep, or is what cause it.
Processing of Emotional Reactivity and Emotional Memory over Sleep:
Bengi Baran, Edward F. Pace-Schott, Callie Ericson, and Rebecca M. C. Spencer
The Journal of Neuroscience, January 18, 2012 • 32(3):1035–1042 • 1035
Sleep enhances memories, particularly emotional memories. As such, it has been suggested that sleep deprivation may reduce posttraumatic stress disorder. This presumes that emotional memory consolidation is paralleled by a reduction in emotional reactivity, an association that has not yet been examined. In the present experiment, we used an incidental memory task in humans and obtained valence and arousal ratings during two sessions separated either by 12 h of daytime wake or 12 h including overnight sleep. Recognition accuracy was greater following sleep relative to wake for both negative and neutral pictures. While emotional reactivity to negative pictures was greatly reduced over wake, the negative emotional response was relatively preserved over sleep. Moreover, protection of emotional reactivity was associated with greater time in REM sleep. Recognition accuracy, however, was not associated with REM. Thus, we provide the first evidence that sleep enhances emotional memory while preserving emotional reactivity.