Researchers at the Netherlands Institute of Neuroscience have taken the first steps in exploring a rather complex question: What is happening inside the brain of a person who may be considered ‘stuck’ between sleep and wakefulness— a state known as sleepwalking?
Many people envision sleepwalkers as individuals wandering around unconsciously with their eyes closed and hands outstretched. In reality, sleepwalkers often have their eyes open and can engage in complex interactions with their surroundings. Sleep scientists refer to these unusual sleep behaviors as “parasomnia,” which can include simple actions like sitting up in bed and appearing confused, but can also involve more complex behaviors such as getting out of bed and moving around or screaming in fear.
While this type of parasomnia is more common in children, about 2-3% of adults also experience it regularly. Parasomnia can be distressing for both the sleepwalker and their bed partner. Francesca Siclari, head of the Dreams Lab, explains: “Those affected can injure themselves or others during these episodes and may feel extremely embarrassed about what they have done afterward.”
There are several abnormal activities occurring inside the brain of a sleepwalker that lead to strange behaviors and experiences. Scientists are still researching to gain a better understanding of this phenomenon.
How Does Parasomnia Occur in the Laboratory?
“It is often believed that dreams only occur during one stage of sleep: REM sleep. However, we now know that dreams can also happen during other stages. People experiencing parasomnia during non-REM sleep sometimes report having dream-like experiences and acting unconsciously.” To understand the causes of these differences in experience, Siclari and her team studied the experiences and brain activity patterns of patients with sleepwalking during non-REM sleep.
Measuring the brain activity of someone during a parasomnia episode is not an easy task. Patients need to fall asleep, go through a stage, and record their brain activity while moving around. “Currently, there are very few studies that can achieve this. But with the many electrodes we use in the lab and some specific analytical techniques, we can now obtain very clear signals, even when the patients are moving around,” Siclari explains.
Siclari’s team can induce a parasomnia episode in the lab, but it requires two consecutive recordings. The first recording captures the patient sleeping normally. The next involves a night where the patient is kept awake and only allowed to sleep the following morning. During this recording, the patient is exposed to loud sounds as they enter deep sleep. In some cases, this leads to a parasomnia episode. Afterward, the patient is asked what occurred in their mind.
Measuring brain activity during a parasomnia episode is quite complex.
During sleep, the human brain typically goes through different sleep stages, 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 in NREM 3, when the body is in deep sleep, but the brain exhibits activity similar to wakefulness. This leads to a lack of synchronization between brain regions controlling movement and cognition, allowing the sleepwalker to perform complex actions without awareness.
The Brain in a Parasomnia State!
In 56% of the parasomnia episodes, patients reported dreaming throughout the episode. “It often involves an impending misfortune or danger. Some people report thinking the ceiling is about to collapse. One patient believed they had lost their child, and others searched the bedding or got out of bed to try to save a ladybug from slipping down the wall and dying,” Siclari explains. “In 19% of cases, patients do not experience anything and simply wake up doing everything, almost like being hypnotized. A small portion reported that they experienced something but could not remember what it was.”
Based on these results, Siclari’s team compared measurable brain activities and found clear similarities. “Compared to patients who do not experience anything, those who dream during this stage show brain activity patterns similar to previously found brain activations associated with dreaming, both right before and during that stage.”
Siclari stated: “Whether a patient remains completely unresponsive or transitions into dreaming seems to depend on their state at that moment. If we activate the brain while they may be dreaming, they seem to be able to ‘create something’ from the activation, while if their brain is largely in a ‘inactive’ state, simple behaviors appear to occur without experience. Interestingly, patients almost never mention the sound that triggered the parasomnia state, instead referencing a different kind of impending danger. The louder we increase the volume, the higher the likelihood we trigger an extreme parasomnia state.”
Since this is just the first step in the research, there are still many other aspects to explore in future studies.
Although much research remains to be done, Siclari is confident that her work can provide valuable insights. “These experiences are very real for patients, and most feel relieved to share them with us. Similar to previous studies, our research clarifies what they are going through, which is valuable from an educational perspective. Additionally, our work may contribute to more specific interventions in future medications. Parasomnia is often treated with non-specific sleeping pills, which are not always effective and can have negative side effects. If we can identify which neural systems are functioning abnormally, we can work towards developing more targeted treatment methods.”
