Parasomnia: What strange things can happen inside a sleepwalker’s brain?

From watching movies, most people imagine a sleepwalker as someone who is unconsciously walking around while their eyes are closed and their arms are stretched out in front of them. In fact, sleepwalkers typically have their eyes open and may have complex interactions with their environment. 

Sleep scientists refer to ordinary sleepwalking as somnambulism – but abnormal sleeping behavior called parasomnia can include simple behaviors like sitting up in bed and seeming confused, abnormal movements, talk, emotions and actions or nightmare disorder, sleep-related eating disorder, sleep paralysis, screaming with a fearful facial expression, and sleep terrors. 

While parasomnias of this type are more common among children, about two to three percent of adults still experience them regularly. Parasomnias can be very upsetting to both the sleeper and the bed partner. “Affected individuals can hurt themselves or others during episodes and may later feel deeply embarrassed for what they did,” said Francesca Siclari, head of the dreams lab at the Netherlands Institute for Neuroscience. 

The study has just been published in the prestigious journal Nature Communications under the title “Shared EEG correlates between non-REM parasomnia experiences and dreams.” 

The researchers have taken a first step in exploring a rather complex question – what is happening inside the brain of somebody who may be considered ‘stuck’ between sleep and wakefulness?

“It was commonly believed that dreams only occur in one sleep stage – rapid-eye-movement (REM) sleep. We now know that dreams can happen in other phases too. Those who experience parasomnias during non-REM sleep sometimes report having dream-like experiences and sometimes appear completely unconscious (on automatic pilot).” To understand what accounts for these differences in experience, they studied the experiences and brain activity patterns of patients with parasomnia in non-REM sleep.

Measuring someone’s brain activity during a parasomnia episode is not simple. The patient needs to fall asleep, experience an episode, and have their brain activity recorded while moving around. “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,” Siclari explained.

How does the lab provoke parasomnia?

To provoke a parasomnia episode in the lab requires two consecutive recordings. For the first recording, the patient sleeps normally. This is followed by a night in which the patient is kept awake and is allowed to sleep only the next morning. During this recording, the patient is exposed to a loud sound upon entering the deep sleep stage. In some cases, this results in a parasomnia episode. After the episode, the patient is asked what had been going through their mind.

In 56% of the episodes, patients reported that they had been dreaming while sleepwalking. “It was often about an impending danger or misfortune. Some reported that they thought the ceiling was going to come down. One patient thought she had lost her baby and was searching through the bedsheets, standing up in bed to try to save ladybugs from gliding down the wall and dying,” Siclari continued. “In 19% of the cases, the patients weren’t experiencing anything and simply awoke to find themselves doing things, almost like a trance.” Another small portion reported that they had experienced something but couldn’t remember what it was.

Based on these three categories, they compared the measured brain activities and found clear parallels. “Compared to patients who didn’t experience anything, patients who dreamt 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.

“What determines whether the patient will be completely unconscious or will instead dream seems to depend on the state the patient is in at that moment,” said Siclari. “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. Interestingly, patients almost never mention the sound that initiated the parasomnia episode, but rather some other type of impending danger. The louder we go with the sound volume, the higher the chance that we provoke an episode.”

The researchers want 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. By measuring brain activity like in this study, we hope to eventually better understand which neural systems are involved in different types of parasomnias.”

While there is still much research to be done, Siclari is certain that her work can provide valuable insights. “These experiences are very real to the patients, and most of them have already felt relieved to be sharing them with us. Our research clarifies what they are experiencing – which is educationally valuable. Additionally, our work could contribute to more specific drug interventions in the future. Parasomnias are often treated with unspecific sleeping drugs, which isn’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.”