The saying 'things will seem different in the morning', rings true as a new study suggests that simply by having a good night's sleep you can decrease the emotional intensity of unpleasant or traumatic experiences.
Researchers from UC Berkeley have found clinical evidence, outlined in the study published in the journal Current Biology suggesting that there is a connection between sleep and affective brain function.
They found that nearly all mood disorders and emotional experiences are processed during sleep to help take the edge off painful memories. They are displayed as sleep abnormalities, commonly involving rapid-eye movement (REM) during the dream phase of sleep where certain stress indicators in the brain are shut down, making the emotional experience more manageable.
"During REM sleep, memories are being reactivated, put in perspective and connected and integrated, but in a state where stress neurochemicals are beneficially suppressed," said Els van der Helm, a doctoral student in psychology at UC Berkeley and lead author of the study.
A typical healthy person spends 20 percent of their sleeping hours in REM, where the troubles from the day are processed reducing next-day subjective emotionality. Building on this evidence the study followed the emotional function of REM sleep, for people with disrupted sleep patterns, including people with mood disorders such as depression and post-traumatic stress disorder (PTSD).
"The dream stage of sleep, based on its unique neurochemical composition, provides us with a form of overnight therapy, a soothing balm that removes the sharp edges from the prior day's emotional experiences," said Matthew Walker, associate professor of psychology and neuroscience at UC Berkeley and senior author of the study.
For people with PTSD, Walker said, this overnight therapy may not be working effectively, so when a "flashback is triggered by, say, a car backfiring, they relive the whole visceral experience once again because the emotion has not been properly stripped away from the memory during sleep."
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The study was conducted using MRI technology to scan the brain activity of 35 healthy adults. They were each shown 150 disturbing, emotional images, twice and 12 hours apart.
Half of the group was shown the images in the morning and again in the evening, before they had the chance to sleep, the second group was shown the images in the evening and had a full night's sleep before being shown the images again for the second time.
The group that had a chance to sleep between viewing the images had a significant decrease brain activity and reactivity in the part of the brain that processes emotions called the amygdala. This indicates that the prefrontal cortex is able to regain control of the participants' emotional reactions, allowing the brain to be more 'rational'.
Walker said he started to investigate the possible beneficial effects of REM sleep on PTSD patients when a physician at a US Department of Veterans Affairs hospital told him of a blood pressure drug that was inadvertently preventing reoccurring nightmares in PTSD patients. "It may also unlock new treatment avenues regarding sleep and mental illness," he said.
So how much sleep is enough to become rational? The University of South Australia's Dr Sarah Jay recommends seven to eight hours sleep per night for adults to be able to reach the deep sleep of REM.
Do you get this much sleep per night?
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