Scientists Discover What’s Happening Inside a Sleepwalker’s Brain

Many adults will experience at least one episode of sleepwalking in their lives, but what is happening inside the brain during these episodes is yet to be uncovered. Researchers from the Netherlands Brain Institute have offered insight into this sleep behavior in their recent study, published in Nature Communications.

Parasomnia can be distressing

Between 66–94% of adults report experiencing at least one instance of abnormal sleep behavior, also termed parasomnia. On the outside, these behaviors can seem like the individual is awake, such as suddenly sitting up in bed, talking or walking around the room.

In certain cases, parasomnia can present itself in more extreme scenarios, including screaming, driving a car or even committing crimes. Parasomnia can cause extreme distress for the sleeper and their family.

“Affected individuals can hurt themselves or others during episodes and may later feel deeply embarrassed for what they did,” said Dr. Francesca Siclari, corresponding author and the head of department in the Sleep and Dreams group at the Netherlands Brain Institute.

Parasomnia can occur in non-REM sleep

It was previously believed that dreams can only occur during REM sleep. However, research has since found they can also happen during other sleep phases. 

“Those who experience parasomnias during non-REM sleep sometimes report having dream-like experiences and sometimes appear completely unconscious (i.e., on automatic pilot),” said Siclari.

The researchers investigated why these differences occur in patients with parasomnia in non-REM sleep.

Studying sleep behavior in a clinical setting

To study a patient's sleep behavior, the individual must fall asleep in a lab, experience a parasomnia episode and have their brain activity recorded without waking up.

“There are currently very few studies that have managed to overcome this. But with the many electrodes we use in the lab and some specific analysis techniques, we can now get a very clean signal, even when the patients move around,” said Siclari.

Participants were monitored for two nights. On the first night, the patients were recorded while they slept normally. The team then induced parasomnia episodes in the participants by keeping them awake through the following night and then allowing them to sleep the next morning. A loud sound was then played to the patients as they entered the deep sleep stage. The patients were asked to record what was going through their minds during the episode.

The sense of impending doom

In 56% of the episodes, participants indicated that they had been dreaming. Many of the participants recorded dreaming about impending danger, and some mentioned they thought the ceiling above them would come down.

“One patient thought they’d lost their baby and was searching through the bedsheets and stood up in bed to try to save ladybugs from gliding down the wall and dying,” Siclari said.

“In 19% of the cases, the patients weren’t experiencing anything and simply awoke to find themselves doing things, almost like a trance.”

A small group of the participants recorded they had experienced something but were unable to remember what it was.

The researchers measured the brain activity of the participants and compared them depending on whether or not they had remembered or experienced something during the episode.

“Compared to patients who did not experience anything, patients who dreamed during the episode showed activations that were similar to brain activations previously found for dreaming, both immediately before the episode and also during the episode,” said Siclari.

The researchers found whether or not the patient was completely unconscious or entered a dream state depended on what state the patient was in at the moment of activation.

“If we activate the brain while they’re likely already dreaming, they appear to be able to ‘make something’ of the activation, while when their brain is largely ‘inactivated’, simple behaviors seem to occur without experience,” explained Siclari.

The patients very rarely mentioned the loud sound that provoked the parasomnia episode. The louder the sound they played, the higher the possibility the team reported an episode occurring.

This is just the beginning

Siclari and the team are hoping their results will eventually lead to an understanding of which neural systems are involved in various parasomnias.

“Ideally, we’d like to set up a system for more people to record their sleep at home, where they may also have much more complex and more frequent episodes. We’d also like to repeat the same type of studies in people who experience parasomnias in REM sleep,” said Siclari.

“Additionally, our work could contribute to more specific drug interventions in the future. Parasomnias are often treated with unspecific sleeping drugs, which aren’t always effective and can have negative side effects. If we can deduce which neural system is working abnormally, we can eventually try to develop more specific treatments.”

Reference: Cataldi J, Stephan AM, Haba-Rubio J, Siclari F. Shared EEG correlates between non-REM parasomnia experiences and dreams. Nat Commun. 2024;15(1):3906. doi: 10.1038/s41467-024-48337-7

This article is a rework of a press release issued by the Netherlands Institute for Neuroscience Material has been edited for length and content.