Sleeping During the Day Enhances Memories of Fear, Emotional Trauma, and Anxiety

Researchers from Ural Federal University (UrFU) and the University of Tübingen (Germany) investigated the effect of sleep in the formation and consolidation of fear memories into long-term memory. Neuroscientists discovered that a short nap improves memory for disturbing and distressing events, but a similar effect of memory improvement was also observed after a period of wakefulness. The study’s findings will be helpful in developing rehabilitation strategies for those who have experienced emotional trauma as a consequence of violent actions, military operations, or natural disasters. The research was published in the journal Cognitive Affective & Behavioral Neuroscience.

Memory consolidation is the process through which memories are transferred from short-term memory to long-term memory. It typically happens when you’re sleeping. Numerous studies have shown that sleeping after learning might have benefits over passively remaining awake. This happens as a result of the reactivation of important memories, which may also be reflected in dreams. The positive effect of sleep can be observed even years later.

However, there are currently no studies that have looked at whether sleep improves fear memory. Therefore, the study attempted to shed light on the subject of what happens to fear memories after a period of sleep and wakefulness.

As Yuri Pavlov says, the fear reaction was studied using electroencephalography. Credit: Nadezhda Pavlova

“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,” says Yuri Pavlov, co-author 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.

He continues, “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.”

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 – the ‘safe’ cue – allowed us 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” explains 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.

- Reference: “Fear memory in humans is consolidated over time independently of sleep” by Yuri G. Pavlov, Nadezhda V. Pavlova, Susanne Diekelmann and Boris Kotchoubey, 14 October 2022, Cognitive Affective & Behavioral Neuroscience. 
DOI: 10.3758/s13415-022-01037-5