No Rest for the Haunted: Sleep May Actually Reinforce Bad Memories

Research suggests that sleep might be responsible for intensifying the emotional response to a troubling event.

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Ever wake up still disturbed -- and haunted -- by the memory of a particularly upsetting image or incident?

A recent study might have an explanation for you.

Research over the past few years has revealed that sleep is intimately tied to memory and might actually be necessary for a large part of its consolidation. Various studies, like the one conducted by Jan Born and Ines Wilhelm, argue that sleep is responsible for the key transition from "newly coded memory representations" to long-term memory storage. As Born and Wilhelm put it, sleep propels this "active system consolidation," which includes the reactivation of memories for processing and eventually preservation.

Researchers are continuing to debate exactly how much each different stage of sleep, such as slow wave (SWS) or rapid eye movement (REM), contributes to consolidation.

Still, a subsequent study published in The Journal of Neuroscience by Rebecca Spencer and her team of researchers at the University of Massachusetts Amherst takes this connection between sleep and memory a step further -- and offers some valuable conclusions in the process.

Divided into two groups, "wake" and "sleep," participants in this study were shown a set of photos -- including a fair number of distressing images -- and were asked to rate each one on a scale of 1 to 9 for both emotional response and arousal. Just twelve hours later, the participants were given a mixed set of photos -- some they had seen before and others that they hadn't. They were again instructed to rate their response and arousal levels.

But the main, and most important, difference between the two groups was that one slept during the twelve hour interval, while the other remained conscious and awake.

The results were pretty insightful (and somewhat unexpected).

"Sleep" participants maintained similar levels of emotional reactivity and arousal for the upsetting (or otherwise called "negative") photos whereas the "wake" group experienced decreased response. These observations translate into a pretty big conclusion: sleep might actually heighten a person's emotional response to a disturbing occurrence.

As the authors of the study put it: "We [are] provid[ing] the first evidence that sleep enhances emotional memory while preserving emotional reactivity."

But these findings are also significant due to the implications they carry. Think about post-traumatic stress disorder: the victim often experiences vivid and intense memories of past traumas during sleep. Could sleep deprivation actually become a treatment for PTSD?

By answering that question, researchers might be able to relieve a lot of suffering. But as an assistant researcher at the University of Pennsylvania's Center for Sleep and Circadian Neurobiology, Olivia Lenz, says, "sleep science is a highly nuanced and complicated field, with many undefined variables."

Still, we have Spencer and her colleagues to thank for getting the ball rolling.