Thursday, 01 December 2011 09:05
While humans spend one-third of their lives sleeping, there is no scientific consensus on the function of sleep.
During the dream phase of sleep, the body’s stress chemistry shuts down, taking the edge off difficult memories. The finding may help explain why people with post-traumatic stress disorder suffer reoccurring nightmares.
“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 the University of California, Berkeley.
For people with PTSD, such as war veterans, this overnight therapy may not work 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.”
Published in Current Biology, the study offers 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 disorders such as PTSD and depression.
While humans spend one-third of their lives sleeping, there is no scientific consensus on the function of sleep. The research unlocks many of the mysteries linking sleep to learning, memory, and mood regulation—and 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,” says lead author Els van der Helm, doctoral student in psychology.
For the study, 35 healthy young adults were divided into two groups and viewed 150 emotional images twice, 12 hours apart, while an MRI scanner measured brain activity.