Many people imagine a sleepwalker as someone who is walking around mindlessly with their eyes closed and their arms outstretched. In fact, sleepwalkers often have their eyes open and can have complex interactions with their surroundings. Sleep scientists call this unusual sleep behaviour ‘parasomnia’, which can include simple behaviours such as sitting up in bed and appearing confused, but also more complex behaviours such as getting out of bed and moving around or screaming with a frightened expression.

Although this type of parasomnia is more common in children, around 2-3% of adults still experience it regularly. Parasomnia can be distressing for both the sleeper and their bed partner. “People affected may hurt themselves or others during the episodes and may feel deeply ashamed afterwards about what they have done,” explains Francesca Siclari, head of the dreams lab.

There is some unusual activity going on in the brain of a sleepwalker that leads to strange behaviors and experiences. Scientists are still working to understand this phenomenon better.

How does parasomnia work in the lab?

“It was commonly believed that dreams only occurred during one stage of sleep: REM sleep. However, we now know that dreams can occur during other stages as well. People who experience parasomnia during non-REM sleep sometimes report having dream-like experiences and acting out unconsciously.” To understand what causes these differences in experience, Siclari and her team studied the experiences and brain activity patterns of patients with parasomnia during non-REM sleep.

Measuring someone’s brain activity during parasomnia is not an easy task. Patients need to fall asleep, go through a stage, and record their brain activity as they move around. “There are very few studies that can do this right now. But with the many electrodes we use in the lab and some specific analysis techniques, we can now get a very clear signal, even when the patient moves around,” Siclari explains.

Siclari’s team was able to induce a parasomnia episode in the lab, but it required two consecutive recordings. The first recording, the patient slept normally. This was followed by a night where the patient was kept awake and not allowed to sleep until the next morning. During this recording, the patient was exposed to loud sounds as they entered a deep sleep stage. In some cases, this led to parasomnia. After this happened, the patient was asked what was going on in their mind.

When people sleep, their brains typically cycle through different stages of sleep, including NREM (non-rapid eye movement) and REM (rapid eye movement). NREM is divided into three sub-stages, from NREM 1 to NREM 3. Sleepwalking usually occurs during NREM 3, when the body has fallen into deep sleep but the brain has the same activity as when awake. This leads to a lack of synchronization between the brain regions that control movement and cognition, allowing the sleepwalker to perform complex actions without being conscious.