They say time heals all wounds, and new research from the University of California, Berkeley, indicates that time spent in dream sleep can help us overcome painful ordeals¹（折磨） . UC Berkeley researchers have found that during the dream phase of sleep, also known as REM sleep, our stress chemistry shuts down and the brain processes emotional experiences and takes the edge off difficult memories.

The findings offer a compelling explanation for why people with post-traumatic stress disorder² (PTSD), such as war veterans, have a hard time recovering from distressing³ experiences and suffer reoccurring nightmares. They also offer clues into why we dream.

"The dream stage of sleep, based on its unique neurochemical composition, provides us with a form of overnight therapy, a soothing⁴（抚慰的） balm（香油） that removes the sharp edges from the prior day's emotional experiences," said Matthew Walker, associate professor of psychology⁵ and neuroscience at UC Berkeley and senior author of the study to be published on Nov. 23, in the journal Current Biology.

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（逆火，回火） , they relive the whole visceral（内脏的，出于本能的） experience once again because the emotion has not been properly stripped away from the memory during sleep."

The results offer some of the first insights into the emotional function of Rapid Eye Movement (REM) sleep, which typically takes up 20 percent of a healthy human's sleeping hours. Previous brain studies indicate that sleep patterns are disrupted in people with mood disorders⁶ such as PTSD and depression.

While humans spend one-third of their lives sleeping, there is no scientific consensus⁷（一致，舆论） on the function of sleep. However, Walker and his research team have unlocked many of these mysteries linking sleep to learning, memory and mood regulation. The latest study shows the importance of the REM dream state.

"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.