If you’ve had a traumatic day, sleeping it off might not be the best idea. 

New research out of the Medical University of Lübeck in Germany suggests that sleep following learning could bolster long-term retention of emotional memories. Therefore, a nap after trauma could increase the likelihood that a patient will develop post-traumatic stress disorder (PTSD), the psychological fallout of a horrific experience. Symptoms of PTSD include nightmares, flashbacks, emotional detachment, clinical depression and anxiety. The research is published in the journal Biological Psychiatry.

Neuroendocrinologist Ullrich Wagner had one group of subjects read a text designed to provoke an emotional response—the passage either detailed the sexual problems of a paraplegic man or the various killing procedures of a child murderer—and a control group read an emotionally neutral text on either bronze sculpture or dressmaking patterns. The subjects rated their emotional reactions to the pieces, and Wagner measured galvanic skin response—the change in the skin’s ability to conduct electricity—to get an objective measure of emotional response. Then half of each group slept for three hours while the others were kept awake.

Four years later, Wagner called his subjects to see if they remembered what they had read. The subjects who read an emotional text and slept afterward exhibited significantly greater recall than any other group. 

“The main finding in the present study is that only three hours of sleep after learning exert a memory-enhancing effect that persists over several years,” Wagner said. 

James McGaugh, a neurobiologist at the Center for the Neurobiology of Learning and Memory at the University of California, Irvine, said Wagner’s results make sense.

“It’s just a fact that we remember accidents, insults, embarrassments, praises, prizes, failures. All of those events are remembered selectively better—either a little better, or a lot better—than emotionally neutral or less exciting events,” he said. “[And] most fair-minded people would say, ‘Yes, if you learn something and fall asleep, there’s pretty convincing evidence that you’re going to remember something better later on than if you learn something and stay awake.’”

But Wagner said the exciting part of the study was the duration of the effect.

“This is remarkable, because normally in studies on sleep effects on memory, the memory test is performed immediately after sleep or wakefulness,” he said. “So it was widely unknown so far how long such sleep effects can persist.”

Wagner noted that his experiments were performed on healthy individuals, so he can’t make any certain conclusions about clinical applications without further study. But he said his findings do suggest that keeping people awake after a trauma could help dull memory formation, decreasing the likelihood that they would develop PTSD.

But our bodies may have already discovered this technique, Wagner said. 

“The frequent observation in cases of traumatic experiences that sleep is disrupted involuntarily in the nights following trauma means that possibly ‘the body’ already knows that sleeping less after the trauma may help to prevent a deeper engraving of the traumatic event in memory,” he said, “which could later result in PTSD.”

Originally published November 20, 2006

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