Sleep may intensify negative emotions, memories

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After undergoing stressful or traumatic events, people often struggle with ways to cope emotionally.  As it turns out, the best solution may be to just stay awake.

A study out of the University of Massachusetts Amherst has uncovered a unique finding regarding a person’s emotional response after witnessing a traumatic or negative event.  For those who stayed awake after seeing negative images, their emotional response was much less intense than those who slept afterward.

In fact, sleep helped to “preserve” the negative events in people’s minds.  And if they were shown the negative item again or recalled it through a mental flashback, their negative emotions about the event were protected – and sometimes even intensified.

“This shows that sleep is an evolutionary advantage,”  said Dr. Rebecca Spencer, assistant professor of psychology at UMass Amherst and one of the lead researchers for the project.  “When you encounter someone who is bad, you should not only remember that person, but you should also remember that emotional memory in order to activate your fight or flight response.”

Spencer and her colleagues presented 106 young adults with a series of images, ranging from negative to neutral in tone.  For the negative images, subjects were shown a picture they might see on the evening news, such as images of a country ravaged by war.  They were then asked to rate their response to each image on a scale of one to nine in terms of happiness and excitement.

Subjects either saw the pictures in the morning so that they would remain awake or they were shown them at night right before going to sleep.  Twelve hours later, each group was shown the images again and asked if they had ever seen them before and how they felt about them.

While sleep helped to preserve a person’s memory of negative images as well their emotional response to them, the scientists found the two processes to be independent of one another during sleep.  The protection of emotional memory was much more closely related to the length of time individuals spent in rapid-eye-movement (REM) sleep period.

“During REM state, the brain is really active – even similar to being awake,” Spencer said.  “So the brain is taking that memory and reprocessing while you sleep.  [It] takes the neural patterns that were fired during wake and replays them during REM.  So there were even some individuals who came back and saw those negative items to be even more negative.”

The study’s findings could have implications for those suffering from post-traumatic stress disorder (PTSD).  Typically those who witness traumatic images or events have difficulty sleeping after the event has occurred.  But Spencer said that reaction may just be the body trying to help remove the negative memory and emotions from the person’s mind.

“Our quick reaction in treating insomnia in people with PTSD might not be best,” Spencer said.  “In those cases, insomnia is a good thing and not letting them sleep is the best response.”

But overall, Spencer doesn’t want negative emotions – or simply emotions in general – to be regarded as necessarily bad to have.  Instead, she hopes to further highlight the need for plenty of sleep to help memory and emotional retention.

“We need to remind people that having these emotions is also good for the average person - just experiencing the ups and downs of your day,” Spencer said.  “If you think of developmentally small kids, they need to sleep a lot.  It allows them to process what they’re learning and how positive and happy certain people feel.”

“There are many advantages for the healthy population in retaining the emotional tone to our memories.”

The study is included in the current issue of the Journal of Neuroscience.