Sleeping Makes Your Bad Memories Even Worse

Many consider sleep to be among the best cures to relieve stress, but researchers from the University of Massachusetts Amherst (UMass), say that sleeping should be the last thing you should do after experiencing psychological trauma.

UMass neuroscientists Rebecca Spencer, Bengi Baran and colleagues, found that by staying awake after witnessing or experiencing something troubling you are more likely to reduce the stressful impact, and by sleeping you actually preserve the bad memory until you wake.

“Today, our findings have significance for people with post-traumatic stress disorder, for example, or those asked to give eye-witness testimony in court cases,” Spencer said.

“We found that if you see something disturbing, let’s say an accident scene, and then you have a flashback or you’re asked to look at a picture of the same scene later, your emotional response is greatly reduced, that is you’ll find the scene far less upsetting, if you stayed awake after the original event than if you slept. It’s interesting to note that it is common to be sleep deprived after witnessing a traumatic scene, almost if your brain doesn’t want to sleep on it,” she explained.

The study, which was published in the current issue of the Journal of Neuroscience involved 68 healthy women, and 38 healthy males between the ages of 18 and 30 years of age. The researchers primary goal was to challenge the assumption that the enhancement of memory that happens as you sleep is linked to a shift in emotional response to memory.

The neuroscience used a polysomnograph, which is a recording of the bio-physiological changes that occur during sleep, and typically is performed at night. Electrodes were attached to the participants scalps to determine if dreaming or other brain activities that happen during the rapid-eye-movement (REM) phase of sleep, affect your emotions once you’re awake.

The experiment was conducted in two separate phases. Subject were shown pictures on a computer screen and asked to categorize each picture as sad or happy. They were also asked to determine if they had a calm or excited response to each photo on a scale of one to nine.

Researchers considered sad-happy ratings and calm-excited ratings from one to three to be negative images, and four to six as neutral images. After 12 hours later, the subjects were shown a combination of new and already viewed photos and asked if it was the first time seeing the pictures, and to rate each one again from the two scales. The participates were also asked to document their ratings in a “sleep-diary”, and afterward take a test.

Out of the participants, 82 were selected either to a sleep group who saw the first set of pictures late in the day and the second group of photos after they slept overnight. The rest of the subjects saw the first set of pictures in the morning and the second set of pictures later that same day. The results were collected from 25 of the subjects who were among the sleep group, and the study was conducted in their own homes during the night.

Rebecca Spencer and her colleagues saw no direct link to REM sleep and the participants accuracy in remembering whether they had seen a picture in both the first and second phases of study, and that sleep caused the subjects to maintain the strength of their initial negative feelings once they witnessed the bad event, compared to if they were awake.

“Sleep may in fact be protective of the emotional salience of a stimulus just as sleep protects the emotional memory”, the authors said.