Investigating the Enigma of Parasomnias
Researchers at the Netherlands Institute for Neuroscience have ventured into the enigmatic realm of sleepwalking, embarking on a groundbreaking study to understand the intricacies of this peculiar state where individuals remain trapped between sleep and consciousness.
Parasomnias: A Spectrum of Sleep Disturbances
Contrary to popular perception, sleepwalkers do not merely stumble around with their eyes closed and arms outstretched. In reality, they often have their eyes open and engage in complex interactions with their surroundings. Sleep scientists categorize such abnormal sleep behaviors as "parasomnias," which can range from simple actions like sitting up in bed and appearing confused to more elaborate ones like leaving bed and wandering around, or screaming in fear.
Although parasomnias are more prevalent in children, approximately 2-3% of adults experience them regularly. These episodes can be distressing for both the sleeper and their bed partners. As Francesca Siclari, head of the Dreams Lab, explains, "People affected by it can potentially harm themselves or others during the episodes, and feel extremely ashamed about what they have done afterwards."
Inside the Sleepwalking Brain
Within a sleepwalker's brain, a peculiar interplay of neural activity unfolds, giving rise to the unusual behaviors and experiences they encounter. Scientists are delving into this enigmatic phenomenon to gain a clearer understanding.
Parasomnias in the Laboratory
"It used to be thought that dreaming was restricted to one sleep stage: REM sleep. However, we now know that dreaming can also happen in other stages," notes Siclari. "Individuals who experience parasomnias during non-REM sleep sometimes report what seem like dream-like experiences and act them out."
To delve into the factors responsible for these variations in experience, Siclari and her team investigated both the experiences and brain activity patterns of patients experiencing non-REM sleep parasomnias.
Measuring brain activity during parasomnias poses significant challenges. The patient needs to fall asleep, enter an episode, and have their brain activity recorded while moving around. "Few studies have been able to do this so far. But with the highly specialized electronic equipment we use at the Dreams Lab and some specific analysis techniques, we can now obtain very clean signals, even when the patients are moving around," Siclari explains.
Siclari's team devised a method to induce a parasomnia in the laboratory setting, but it required two consecutive recordings. In the first recording, the patient had a normal night's sleep. In the following one, the patient was kept awake and only allowed to fall asleep the following morning. During this recording, once the patient entered deep sleep, they were exposed to a loud sound. In some cases, this triggered a parasomnia episode. After the event, the patients were interviewed about their subjective experiences.
The Interplay of Consciousness and Dreams
As the brain cycles through different sleep stages during the night, humans experience non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. NREM is further divided into three sub-stages, NREM 1 to 3. Sleepwalking typically occurs during NREM stage 3, a time when the body is in deep sleep but the brain exhibits patterns similar to wakefulness. This leads to a desynchronization between brain areas controlling motor function and cognition, allowing sleepwalkers to perform complex actions without conscious awareness.
During the parasomnias induced in the study, 56% of the episodes involved the patient reporting that they had been dreaming. "It is often about something unfortunate or dangerous happening. Some people say they felt like the ceiling was coming down. One person thought they had lost their child, and others reported getting out of bed or crawling around in the sheets trying to save a beetle that had fallen off a wall," says Siclari. "In 19% of the cases, the person did not experience anything, but simply woke up and found themselves doing something, almost like they were in a trance. And in a smaller percentage, they reported experiencing something but could not say what it had been."
Analyzing the brain activity measurements, Siclari's team found striking parallels. "Compared to those who did not experience anything, the patients who dreamed during these episodes showed activation patterns in brain areas that had previously been found to be involved in dreaming, both in the period just before and during the episode."
"What seems to determine whether the patient will experience dream-like content or black out appears to depend on the state of their brain at that point in time," Siclari explains. "If we triggered the event while they were prone to dream, they seemed able to 'make something' out of the stimulus, whereas when their brain activity was more 'switched off,' the simple behaviors appeared to happen without any experience. Interestingly, the patients almost never reported the triggering sound in their stories, but instead dreamed that they were in some other kind of imminent danger. The louder we made the sound, the more likely we were to trigger a more dramatic parasomnia."
Implications and Future Research
Although this research represents only a first step, Siclari is optimistic that its insights will prove invaluable. "These experiences are very real to the patients, and sharing them with us often comes as a relief. Similar to previous studies, our research validates what they go through, which has educational value in itself. Additionally, our work may contribute to more specific drug interventions in the future. Parasomnias are often treated using non-specific sleep medication, which is not always effective and can have negative side effects. If we can pinpoint the specific neurotransmitters that are malfunctioning, we may be able to develop more targeted treatments."