Dreaming, also known as REM sleep, suppresses stress chemicals while the brain processes emotional experiences, reducing the burden of painful memories, according to new research from the University of California, Berkeley.
This could also explain why war veterans and other sufferers of post-traumatic stress disorder (PTSD) have recurring nightmares, and difficulties overcoming painful memories.
“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 study author Matthew Walker in a press release.
PTSD sufferers may not be receiving the therapeutic benefits of REM sleep, Walker said, explaining that events like a car backfiring can trigger a flashback that makes them “relive the whole visceral experience once again because the emotion has not been properly stripped away from the memory during sleep.”
Humans spend about one third of their lives asleep, with REM sleep comprising about 20 percent of a healthy person’s sleep time. Past brain studies have revealed that mood disorders like depression and PTSD are associated with broken sleep patterns. The new findings offer new insights into the importance of REM sleep on emotional function.
“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 study lead author Els van der Helm in the release.
The researchers studied 35 healthy young adults in two groups. Each group viewed 150 emotionally stimulating images twice, 12 hours apart. One group stayed awake between viewings while the other slept. Brain activity was measured with magnetic resonance imaging (MRI), whilst viewing the images and during sleep.
Participants who slept between viewings demonstrated a decreased emotional response to the images with reduced activity in the brain’s emotional processing center (the amygdala) during viewing, and a reduction in stress chemical release in the brain.
“We know that during REM sleep there is a sharp decrease in levels of norepinephrine, a brain chemical associated with stress,” Walker said.
“By reprocessing previous emotional experiences in this neuro-chemically safe environment of low norepinephrine during REM sleep, we wake up the next day, and those experiences have been softened in their emotional strength,” he continued. “We feel better about them, we feel we can cope.”
These findings may lead to new treatment options for sufferers of PTSD, sleep disorders, and mental illness.
The study was published in the online journal Current Biology on Nov. 23.