Sleep solidifies bad feelings

A night of shut-eye sears bad feelings into the brain, while waking hours take the emotional edge off, a new study finds. Though preliminary and somewhat inconsistent with earlier research, the results suggest that staying awake after something awful happens might be a way to blunt the emotional fallout of traumatic experiences, researchers report in the Jan. 18 Journal of Neuroscience.

Sleep is known to lock in memories, particularly emotional ones, but scientists didn’t know whether accompanying feelings are locked in, too — a question that’s particularly relevant to people who suffer from post-traumatic stress disorder.

“If we really want to know if this is relevant to trauma survivors, then we need to know if sleep not just changes the memory, but if it changes how you feel about it if you experience it again,” says study coauthor Rebecca Spencer of the University of Massachusetts Amherst.

In the study, Spencer and her colleagues showed pictures of neutral scenes, such as a street, or negative scenes, such as an upsetting car crash, to 106 young adults. Participants then rated the emotion inspired by the image on a one-to-nine scale ranging from sad to happy. Afterward, participants were either sent to bed for a full night’s sleep or asked to stay awake for 12 hours. Then the researchers retested the participants by showing some of the same pictures mixed in with new images.

As expected, the people who slept were better at remembering which images they had seen the day before. But the memory wasn’t the only thing that stuck around: Sleepers held on tighter to their feelings, while the sadness scores given by people who stayed awake tended to be weaker in the second session.

Cognitive neuroscientist Jessica Payne of the University of Notre Dame in Indiana finds the results “tremendously tantalizing,” but cautions that they are too preliminary to be the basis of any recommendations about how much or little to sleep after experiencing trauma. “It is way too soon, way too premature, to talk about treatments for PTSD. We need to have an extensive body of work before we get out there and start saying things like that.”

Payne points out that sleep deprivation leads to increased stress, which can profoundly influence emotions. “In most cases, it’s better to sleep than to not sleep,” she says.

These new results contrast with a study published in December that found that a night of sleep takes the emotional edge off unpleasant experiences — what some scientists call overnight therapy. That study, led by Matthew Walker of the University of California, Berkeley, used different methods and measurements, which may be responsible for the seemingly opposite findings, says neuroscientist Penny Lewis of the University of Manchester in England.

“It seems like the system is more complicated than we had thought,” she says, “and we need to run more experiments to figure out what is going on.”