|According to Yuri Pavlov, the positive effect of sleep on memory can be observed years later. |
Photo Credit: Nadezhda Pavlova
Scientists from Ural Federal University and the University of Tübingen (Germany) studied the effect of sleep on the formation and translation of primary memories of something scary into long-term memory. Neurobiologists discovered that sleeping during the day strengthens memory of disturbing and frightening events, but a similar effect of memory strengthening is also observed after a period of calm wakefulness. The findings will be useful for developing rehabilitation strategies for people who have been emotionally traumatized by disasters, warfare, and violence. The study was published in the journal Cognitive, Affective, & Behavioral Neuroscience.
Memory consolidation - the transition of memories from short-term memory to long-term memory - occurs primarily during sleep. Studies show that sleep after learning can have positive effects that are superior to passive wakefulness. This occurs by reactivating important memories, which may also be reflected in dreams. The positive effects of dreaming can be observed even years later. However, there are currently no studies that analyze whether sleep enhances the effect of remembering emotionally difficult events. Therefore, scientists decided to find out how sleep affects the memory of a person's experience of fear.
"Understanding the effect of sleep-in situations where emotional trauma occurs is important for shaping effective behavioral strategies with survivors of any disaster, people with panic disorder or post-traumatic stress disorder. If we found that the effects of sleep on fear memory were similar to other types of memory, such as episodic memory (memory of life events), then it would be beneficial for survivors to stay awake after trauma. In our experiments, we determined that a two-hour nap during the day reinforced memories of anxiety, which we induced in subjects just before going to bed. However, a similar effect was observed when comparing it to a period of calm wakefulness - watching an emotionally neutral movie or a computer game," says Yuri Pavlov, a researcher at the Academic and Research Laboratory of Neurotechnologies of Ural Federal University and the Institute of Medical Psychology and Behavioral Neurobiology at Tübingen University, the co-author of the article.
Before and after the sleep period, participants underwent a fear conditioning paradigm, namely listening to a stimulus sound. Participants in the experiment first heard a neutral sound, and then it was periodically combined with a noise, the expectation of which causes anxiety and fear. Researchers note that many rate this stimulus as more unpleasant than even electric shocks, also often used in studies of fear.
"To form emotions and conditioned reflexes, it is often sufficient to combine a neutral stimulus (conditioned stimulus) many times with a stimulus that naturally produces an emotion (unconditioned stimulus). Subsequently, the neutral stimulus starts an equally strong emotional response on its own. In our study, we combined a neutral sound, a conditioned stimulus that initially elicits no reaction in the body, and noise, an unconditioned stimulus that predicts the appearance of a very loud sound that people find extremely unpleasant. As a result of current research, we show that the fear reaction only to a neutral sound is formed and intensified after sleep", explains Yuri Pavlov.
The fear response was studied using electroencephalography before and after sleep or an equal period of wakefulness in 18 healthy young adults. The researchers are now moving the research to the clinic, where they plan to test patients in a vegetative state and a state of minimal consciousness to determine how sleep will affect their level of anxiety and the formation of memories of fear. They also note that further research is needed on the effects of longer periods of sleep.
Fear-related disorders, such as panic disorder, post-traumatic stress disorder (PTSD) or specific phobias, arise against the background of having undergone stress. They are characterized by constant feelings of anxiety and fear, which may intensify over time.
Memory consolidation is the process of transitioning primary memories into a stable long-term form. Studies of declarative (memory for facts), episodic (memory for life events), and procedural (memory for skills) memory show that sleep after learning has a positive effect.
A person's sleep cycle is usually about 1.5 hours. People sleep four to six cycles at night. If they also resort to rest in the form of daytime sleep, they rarely sleep more than one full cycle during the day.
Source/Credit: Ural Federal University