Fear in dreams and in wakefulness: evidence for day/night affective homeostasis
Despite partial experimental evidence, it is a long-standing and common belief that dreams serve an emotion regulation function. Revisiting this idea, recent neuroscientific theories have proposed that emotions experienced in dreams contribute to the resolution of emotional distress (e.g. fear extinction) and preparation for future waking affective reactions. Here we addressed one emerging common prediction from these theoretical accounts, namely that experiencing fear in dreams is associated with more adapted responses to threatening signals during wakefulness. Using a stepwise approach across two studies, we first identified brain regions activated when experiencing fear in dreams and then showed that frightening dreams modulated the response of these same regions to threatening stimuli during wakefulness. As predicted, more fear in dreams was associated with reduced activation of those fear-responsive regions during wakefulness. Specifically, in Study 1, we performed serial awakenings in 18 participants recorded throughout the night with high-density EEG and asked them whether they experienced any fear in their dreams. Insula activity increased (i.e. decreased delta and increased gamma power) for dreams containing fear. In Study 2, we tested 89 participants and found that those with higher incidence of fear in their dreams showed reduced fMRI response to fear-eliciting stimuli in the insula, amygdala and midcingulate cortex, while awake. Consistent with better emotion regulation processes, the same participants also displayed increased medial prefrontal cortex activity. These findings support that emotions in dreams and wakefulness engage similar neural substrates, and substantiate a link between emotional processes occurring during sleep and emotional brain functions during wakefulness.