Sleep has been shown to have a long list of physical and mental health benefits, and now a new study suggests it could also help to “erase” bad memories.

That’s according to researchers from the University of Hong Kong, who implemented a procedure called “targeted memory reactivation” (TMR) to reactivate positive memories and weaken painful ones during sleep. 

“Recollecting painful or traumatic experiences can be deeply troubling,” the researchers wrote in the findings, which were published in the journal PNAS. “Sleep may offer an opportunity to reduce such suffering.”

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“We developed a procedure to weaken older aversive memories by reactivating newer positive memories during sleep.”

In the study, a total of 37 participants were shown 48 “nonsense words,” each paired with a different unpleasant image, before going to sleep for the night.

The next evening, they were shown half of the words paired with positive images from four categories: animals, babies, people and scenes. 

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During the following “non-rapid-eye-movement” sleep, the researchers introduced “auditory memory cues.” 

When the participants woke, they had less memory of the negative images and stronger memory of the positive ones.

“Our results were aligned with recent TMR research showing that episodic forgetting could be induced via reactivating interfering memories during sleep,” the researchers wrote in the study.

“Going beyond prior research on neutral memories, our results suggest that TMR preferentially reactivated recently acquired positive memories and weakened older aversive memories, thus altering the fate of emotional experiences.” 

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Dr. Earnest Lee Murray, a board-certified neurologist at Jackson-Madison County General Hospital in Jackson, Tennessee, noted that TMR has been a method for treating PTSD and other aversive (bad) memories.  

“This is done by combining sensory cues with therapeutic interventions and then re-presenting these cues during specific sleep phases,” Murray, who was not involved in the study, told Fox News Digital. 

This treatment has been shown to reduce the emotional impact of aversive memories, the neurologist added.

“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,” Murray said. “This will open the door for additional research in ways to weaken traumatic or other bad memories.”

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In addition to psychotherapies, medications are sometimes used to suppress nightmares or other aversive memories, he noted. 

“This study continues to show ways to treat these conditions without the use of medications, which oftentimes are fraught with adverse side effects.”

Alex Dimitriu, MD, a board-certified psychiatrist and sleep medicine doctor and founder of Menlo Park Psychiatry & Sleep Medicine in California, was also not involved in the study, but said it is “fascinating” in what it reveals about how the brain processes memories during sleep.

“Our brains are unpacking, processing and repacking emotions in our sleep,” he told Fox News Digital. “I had suspected this before, and have often told my patients that sleep is like therapy for our emotions.”

Many of the doctor’s patients have reported improvements in mood and anxiety when sleep was improved.

“There has been evidence that in REM (dream sleep) in particular, a lot of emotional processing and rehearsal occurs,” Dimitriu said. “In this study, however, the intervention was in non-REM sleep, which shows that emotions are processed in other sleep phases as well.”

The process of using TMR to suppress negative emotions and fortify positive memories could have a “tremendous impact” on people with depression or trauma, the expert said.

“I am excited to see further research into this area, which essentially means we can learn and change while we are asleep.”

Potential limitations

The study did have some limitations, the researchers noted.

“Our brains are unpacking, processing and repacking emotions in our sleep.”

“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 wrote. 

It can also be difficult to find positive components within some highly traumatic experiences, they noted. 

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“Future research should explore ways to introduce positive interfering memories, such as positive autobiographical memories or therapy-related memories, to effectively weaken real-life trauma memories,” the researchers stated. 

“Second, the role of REM sleep in modulating emotional memories shall be further investigated.”

The study received ethical approval from the Human Research Ethics Committee of the University of Hong Kong.

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Funders included the Ministry of Science and Technology of China and the National Natural Science Foundation of China, along with other grants.

Fox News Digital reached out to the researchers for comment.