After an emotionally stressful day, dreaming can help in coping with distressing memories, according to a UC Berkeley study published Nov. 23 in the journal Current Biology.

The study, which shows that rapid-eye movement sleep can decrease emotional intensity in reaction to past events, is the first to systematically test how sleep affects reactivity to previous emotional experiences at both a brain and behavioral level.

“It’s the first to look at REM sleep in such a sophisticated way,” said Els van der Helm, a UC Berkeley doctoral student in psychology and lead author of the study, in an email. “It aids therapies not only for (post-traumatic stress disorder) but also mood disorders.”

According to the research — which was conducted over one and a half years — REM sleep creates an ideal environment for the brain to process emotions because it reduces stress-inducing electrical activity patterns and activity of some
neurotransmitters.

“We believe this unique brain state helps to put these emotional experiences ‘in perspective’ by integrating them with previous memories while ‘stripping away’ the emotional tone associated with them,” van der Helm said in the email.

The study is the first to record sleep’s effect on both brain activity and behavioral reactions to emotional experiences. Researchers tracked activity in the emotional regions of the brain and measured how intensely participants rated the emotional images that were shown to them during the study after REM sleep.

Researchers also noticed that the aggressive reactionary forces of the brain’s emotion-processing area — the amygdala — decreased as a result of REM sleep, allowing the rational part of the brain to regain control of the individual’s emotional reactions.

During REM sleep, neurotransmitters that play an important role in memory processing are more active. The heightened presence of these chemicals, as well as reduced stress, allows the brain to process emotions most beneficially during the most vivid dreams, van der Helm said in the email.

“The finding that REM sleep physiology is associated with … amygdala activity in response to previous emotional experiences … the next day has some very exciting implications for treatment of mood and/or anxiety disorders,” said Carrie Bearden, associate professor of psychiatry and biobehavioral sciences and psychology at UCLA, in an email. “It’s a very innovative study.”

For the study, researchers showed images invoking intense emotional response to 35 healthy young adults twice with a 12-hour interval in between.

Participants who were allowed to sleep between the two viewings showed a significantly less intense reaction to the images the second time around compared to those who stayed awake.

“This research shows that sleep plays a crucial role in emotional processing and opens up doors for therapeutic avenues,” van der Helm said in the email.

The study focuses particularly on the condition of post-traumatic stress disorder, characterized by REM abnormalities and exaggerated amygdala reactivity where “sleep problems are often part of the diagnostic criteria, but often go untreated,” van der Helm said in the email.

Patients with post-traumatic stress disorder and other mood disorders can benefit from improved therapeutic sessions using the findings in the study, he said in the email.

“It would be interesting to conduct a longer-term study to examine cross-lagged effects of changes in amygdala reactivity and subjective emotional reactivity over time,” Bearden said in the email. “The relationship of REM sleep to emotional response is surprisingly under-studied so I think this is a great step in that direction.”