Scientists studied the effect of sleep on the formation and consolidation of memories of emotional trauma into long-term memory.
Neuroscientists from the Ural Federal University (UrFU) and the University of Tübingen in Germany have found that a short nap enhances the memory of disturbing and fearful events, but a similar effect of enhancing memory was also observed after a period of wakefulness.
The results of the study may be useful for developing strategies for the rehabilitation of people who have received emotional trauma during natural disasters, military operations, and acts of violence, researchers say. The study was published in Cognitive, Affective, & Behavioral neuroscience.
“Understanding the effect of sleep in situations where emotional trauma occurs is important for developing effective strategies for coping with disaster victims, people with panic or post-traumatic stress disorder. If we found that the effect of sleep on fear memory is similar to other types of memory, such as episodic memory (memory of life events), then it would be more beneficial for victims not to sleep after the trauma. In our experiments, we determined that a two-hour daytime nap reinforces the memories of fear learned just before sleep. However, a similar effect was observed after wakefulness – watching an emotionally neutral movie or a computer gaming similarly enhances fear memories,” says Yuri Pavlov, coauthor of the article, researcher at the laboratory of Neurotechnology of UrFU and the Institute of Medical Psychology and Behavioral Neurobiology at the University of Tübingen, in a statement.
Before and after sleep, the participants went through a fear conditioning paradigm. The participants in the experiment first heard a neutral tone, and then it was always paired with a loud noise, another tone was never paired with the noise, says the scientist.
“After multiple pairings, the neutral stimulus evoked an equally strong emotional response on its own. Interestingly, people typically rate the loud noise as more unpleasant than even electric shocks, also often used in fear research. The comparison between tones paired with the highly aversive noise and the other tone — ‘safe’ cue — allowed to investigate neural processes behind fear learning. We found that the neural signatures of fear learning enhanced after a nap, and in equal measure after short rest,” says Yuri Pavlov.
The fear-conditioned responses were studied by electroencephalography before and after a 2-hour daytime nap or an equal period of wakefulness in 18 healthy young people. The researchers are now moving the study to the clinic, where they plan to test patients in a vegetative state and a minimally conscious state to determine how sleep will affect their levels of anxiety and the formation of fear memories. They also note that further study of the effect of a longer sleep period is needed.
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