A new study sheds more light on the relationship between sleep and memory preservation, and shows that sleep may actually help to protect our positive memories.
Researchers found that "sleep enhances our emotionally positive memories while these memories decay over wake," study researcher Rebecca Spencer, of the University of Massachusetts, Amherst, said in a statement. "Positive memories may even be prioritized for processing during sleep."
The study was presented at the 19th annual meeting of the Cognitive Neuroscience Society.
The researchers conducted their study on 70 young adults. At the beginning of the study, all of them looked at pictures of "happy" things, like puppies and flowers, as well as neutral things like dinner plates. Their emotional reactions and memories of these images were tested. Then, some of the study participants were kept awake for an overnight period, while the others were allowed to sleep.
After that period of sleep or wakefulness -- which was 12 hours long -- the researchers again tested the study participants' emotional reactions and memories of the images. They found that the people who were allowed to sleep more often remembered the positive pictures than the neutral ones, which links their sleep with the processing of these positive images.
The results of the study could play a part in PTSD treatment, Spencer said.
"It suggests that insomnia should be treated at some point after a traumatic event –- perhaps a few days/weeks depending on the level of trauma –- so that these positive memories can be strengthened and eventually outweigh the negative," she said in the statement.
But on the other hand, research published earlier this year in the Journal of Neuroscience from the same researcher showed that sleeping on negative thoughts could actually make those experiences seem more disturbing.
"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," Spencer said in a statement for that study. "It's interesting to note that it is common to be sleep-deprived after witnessing a traumatic scene, almost as if your brain doesn't want to sleep on it."