A recent international study suggests that sleep may help erase bad memories by reactivating positive ones during non-rapid eye movement (NREM) sleep. Researchers from the University of Hong Kong conducted the study using a procedure called targeted memory reactivation (TMR) to enhance positive memories and weaken painful memories during sleep, according to the New York Post.
In the experiment involving 37 participants, the researchers asked volunteers to associate random words with negative images, including human injuries and dangerous animals. They also used recognized databases of images classified as negative or positive. To interfere with the negative associations, participants were then shown half of the words paired with positive images from four categories: animals, babies, humans, and landscapes.
During NREM sleep, the researchers introduced auditory memory cues by playing recordings of the nonsensical words that participants had uttered. This method aimed to reactivate specific memories during sleep, thereby influencing the consolidation of those memories. The researchers measured the participants' brain activity with electroencephalography (EEG) during this process.
Upon waking, participants had less memory of the negative images and stronger memory of the positive ones, as their memories were reinforced by sleep, reported the New York Post.
"We found that this procedure weakens memory of unpleasant memories and also increases unconscious intrusion into positive memories," the researchers wrote, according to Science Alert.
"This study not only shows a suppression or a weakening of aversive memory but does so by reactivating newer positive memories while the patient is asleep. This will open the door for additional research in ways to weaken traumatic or other bad memories," said Dr. Ernest Lee Murray, a board-certified neurologist, according to the New York Post.
The study was a tightly controlled laboratory experiment, which is good for trusting the accuracy of the results, but it has limitations. The researchers acknowledged that "the effect of viewing negative images in the laboratory on memory formation is not the same as experiencing a real painful event."
"First, although our experiment aims to weaken aversive memories, the lab-induced emotional experiences of viewing aversive/positive images may not mimic typical traumatic experiences," they added.
"This study is fascinating because it reveals new information about how the brain processes memories during sleep," said Dr. Alex Dimitriu, a psychiatrist and founder of the Menlo Park Psychiatry and Sleep Medicine Center in California, as reported by the New York Post. "I am excited to see further research into this area, which essentially means we can learn and change while we are asleep," he said. "Evidence had shown that during REM sleep, processing, repetition, and regulation of emotions occur in the mind, but in this study, the intervention was in non-REM sleep, indicating that emotions are processed in other sleep phases as well," he noted.
The researchers emphasized the potential clinical applications of their findings. "In general, our findings may provide new relevant perspectives for the treatment of pathological or trauma-related memory," they wrote. However, they also noted the challenges in applying this method to real-life traumatic memories. "Finding positive aspects in severely traumatic and distressing experiences is not easy," they stated. "It can also be difficult to find positive components within some highly traumatic experiences."
Sleep has a long list of physical and mental health benefits, including improvements in mood and anxiety when sleep quality is enhanced. "Our brains are unpacking, processing, and repacking emotions in our sleep," Dr. Dimitriu explained, according to the New York Post.
The study's funding sources included the Ministry of Science and Technology of China and the National Natural Science Foundation of China, along with other grants. The research was published in the journal PNAS last July and would have gone almost unnoticed if not for its recent revival by Fanpage, reported Il Fatto Quotidiano.
The article was written with the assistance of a news analysis system.