Scientists have unlocked one of the great mysteries of the human experience, how we deal with traumatizing experiences that could leave us emotionally crippled. It happens during an "elegant ballet of biology" that softens painful memories, according to psychologist and neurologist Matthew Walker of the University of California, Berkeley, who led the research team.
And here's the amazing part: It all happens while we sleep. Our dreams help us heal.
"When you snooze you win," Walker said during a telephone interview.
Walker's team produced strong evidence that supports an assumption among scientists that a specific phase of sleep, called rapid eye movement, or REM, plays a key role in helping us deal with troubling emotions. Until now, there has been "little to no" evidence that's true, and there was even less understanding of how it works.
But the Berkeley team found that during REM, which is also the time we dream, stress chemicals are suppressed in the "emotional hub" of the brain called the amygdala. The research shows that after a good night's sleep, even potentially traumatizing experiences are softened.
"During REM sleep, memories are being reactivated, put in perspective and connected and integrated, but in a state where stress neurochemicals are beneficially suppressed," Els van der Helm, a doctoral student in psychology at Berkeley, said in releasing the study, published in the journal Current Biology.
About 20 to 25 percent of the time an adult spends sleeping is spent in REM, and scientists have suspected that REM plays a critical role in helping us deal with emotions because patients suffering with post traumatic stress disorder (PTSD) also suffer from sleep disorders, especially involving the REM phase.
"We've heard all our lives that if we are troubled, we should get to bed," Walker said. "We'll feel better tomorrow." But is that right?
The researchers put 35 "healthy young adults" through hours of lab-induced stress to see if there is any evidence that those old bromides are really true.
All of the participants spent two sessions inside a magnetic resonance imager, 12 hours apart. While their brains were being scanned for neurochemical activity, they were shown 150 images ranging from benign, like a friendly cat, to highly emotional, like a snake with fangs, or a burn victim.
The participants were divided into two groups. The members of one group had their first scan early in the day and their second 12 hours later, with no time to sleep between the sessions. The other group had one scan in the evening and the second the next morning, after sleeping in a controlled environment in the university's sleep lab.
As they viewed the images, all the participants "had a short period of time when they could rate the emotional intensity they were feeling in response to that individual image," Walker said. "That allowed us to get a subjective measure of how they themselves were feeling in response to those emotional images."
But the scanner also produced an objective measurement of the emotional reaction. In the first session, the amygdala literally "lit up" because of a strong reactivity by chemicals associated with stress. That was true for both groups.
The second session tells the story. The group that had no sleep experienced even stronger neurochemical reactivity when shown the images than they had during the first session. But the group that had a full night's sleep had relatively mild reactions to the images.
"That's a strong signal that tells you it wasn't just the passage of time that healed the wounds," Walker said. "It was sleep that caused the reduction in emotional reactivity."
And electroencephalographs of the participants who spent the night in the sleep lab pinpointed the times during the night when the chemicals were suppressed. It happened during the REM phase.
The dream phases of sleep allowed the participants to "cope" with their emotions, so when they saw the images the second time they could remember them from the first session, but without experiencing the emotional trauma again, he added.
Unfortunately, for PTSD victims, the pain remains, apparently because the REM phase is not doing what it ought to do. So a soldier who hears a car backfire may relive the terror of a combat experience because the emotional wounds are still open.
For the rest of us, a good night's sleep will at least soften the emotion.
"Mother nature has programmed us with some elegant biology that naturally does its thing every time we allow our heads to hit the pillow for a sufficient amount of sleep," Walker said.
"But we are in a society now that is desperately shortchanging our brains emotional regulation potential because we don't allow ourselves sufficient sleep.
"The average now seems to be below seven hours for the U.S. That's frightening."