New studies from the Department of Psychology, Harvard University show

That going to sleep after experiencing negative emotions appears to reinforce or “preserve” them.

In the study, scientists recruited 106 men and women and exposed them to images that created various emotions. In some cases, the emotions were negative, for example, after seeing an unsettling image of an accident or traumatic scene. In other cases, the images produced positive or neutral emotions.

The researchers studied what happened when the subjects were shown both new images and the previous ones 12 hours later. Some either in the morning after a full night of sleep or at the end of a full day of being awake. They also measured the brain activity and the rapid eye movement, or REM, phase of sleep, which is when dreams occur.

The scientists found that staying awake blunted the emotional response to seeing the upsetting images again. But when the subjects were shown the disturbing images after a night of sleep, their response was just as strong as when they had first seen them, suggesting that sleep “protected” the emotional response.

Other studies have found that sleep actually enhances emotional memories. The authors pointed out that after an unsettling experience, many people have trouble sleeping, perhaps the brain’s way of trying to keep the memory or emotions from being stored.

The effects of an argument therefore may be greater after sleep than what they would be if resolved prior to going to bed.

Processing of Emotional Reactivity and Emotional Memory over Sleep

Department of Psychology and Neuroscience and Behavior Program, University of Massachusetts