Emotional Processing Function
Category: Sleep Science
The Dreams as Overnight Therapist Hypothesis
Neuroscientist Matthew Walker positioned REM sleep dreams as overnight emotional therapy. According to this hypothesis, when emotional memories are reactivated during dreams, they are processed in a state where noradrenaline (stress hormone) secretion is suppressed. The content of emotional events is retained in memory, but the accompanying emotional pain is gradually stripped away. On this hypothesis, feeling less distressed about the same event the next morning would mean that dreams took on the work of emotional desensitization overnight.
PTSD Nightmares - A Broken Emotional Processing Device
Recurring trauma nightmares in PTSD patients can be understood as emotional processing function breakdown. Normal dreams reprocess emotional memories in a safe noradrenaline-suppressed environment, but in PTSD this suppression fails. Each time trauma memories are reactivated in dreams, stress responses equivalent to waking occur, preventing emotional desensitization. The dream ends up working on the side of re-traumatization rather than on the side of treatment. Treatments that try to restore this mechanism with medication have been attempted, but what smaller trials reported as effective failed to show an effect in the largest trial to date, and the question is not settled. When trauma nightmares persist over a long stretch, what to rely on is not the name of a particular drug but the judgment of a medical provider specializing in post-trauma care.
Why Unpleasant Dreams Are Necessary
After an unpleasant dream, when the day that follows goes badly, it is easy to put the whole thing down to having had a bad dream. But the causality may run the other way: it is because strong emotional stress was experienced during the day that the brain generates emotional dreams in order to process it. Seen through this hypothesis, unpleasant dreams are placed not as symptoms of illness but as part of the process of recovery itself. A run of emotionally intense dreams after a separation or a loss can be read as a sign that there is still that much feeling waiting to be processed. If so, rather than trying to cancel out the unpleasantness of the dream, giving words during the day to the emotion the dream is handling is the path that lies closer to recovery.
Neural Mechanisms of How Sleep Deprivation Destabilizes Emotions
Sleep deprivation pushes the next day's emotional reactivity sharply upward. And when sleeping hours are cut, what is lost first is the latter half of the night, where REM sleep is concentrated. The fMRI study by Yoo et al. (2007, Current Biology) reported that in people kept awake through a night, amygdala (the emotional center) reactivity was heightened while regulation by the prefrontal cortex weakened. What this experiment removed was an entire night of sleep, not REM sleep on its own. Even so, the fact that the loss of a single night tips a person toward the side that cannot hold emotion in check supports the view that the settling of emotion is work carried out overnight. The everyday experience of being short-tempered when short on sleep can be taken as the body reporting that the emotional processing function of dreams has not had enough room to do its job. The unglamorous habit of not cutting into the early-morning stretch of sleep is what holds emotional stability up.
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