(Inside Science) -- Writers over the centuries have analyzed the activity of sleepwalkers, from Shakespeare’s Lady Macbeth to the murderous somnambulist in the 1920 German movie The Cabinet of Dr. Caligari. But modern scientists find it difficult to study real life sleepwalkers, because their excursions are episodic and unpredictable.
Now, however, a team of European scientists has developed a new method of studying the condition. They tested sleepwalkers’ ability to multitask while they were awake, and compared the results with those from non-sleepwalkers.
The result: Sleepwalkers can perform a basic multitask -- walking and counting backwards out loud -- more effectively than non-somnambulists. That apparently simple finding provides useful insight into the change in awareness that occurs during sleepwalking.
“Our research offers novel insights into this common sleep disorder and provides a clear scientific link between action monitoring, consciousness and sleepwalking,” said team member Oliver Kannape, lecturer in cognitive neuroscience at the University of Central Lancashire in England. “You can learn a lot of neuroscience by studying brains that are different.”
“This most interesting study buttresses the growing concept that disorders of arousal, such as sleepwalking, represent a dissociation of wake/sleep states resulting from an admixture of wakefulness and non-REM sleep,” said Mark Mahowald, retired professor of neurology at the University of Minnesota Medical School, who was not involved in the project. “The study suggests that some degree of such dissociation may even exist during the apparent full-waking state. This fascinating finding is supported by the fact that as a group, sleepwalkers experience more objective sleepiness during the day than non-sleepwalkers.”
Information from the study can also affect clinical decisions.
Diagnosing sleepwalking behavior is complex and time-consuming, since it traditionally requires observations in a sleep laboratory. But in the multitasking experiment, Kannape team's correctly predicted 10 out of 11 sleepwalkers using data gathered solely when the individuals were awake.
And by focusing on sleepwalkers’ change in awareness during the experiment, the study has sociological implications.
“This change is really quite striking, as it links to the concept of culpability and the medico-legal issues surrounding sleepwalking,” Kannape added. Legal authorities in several countries have argued about whether sleepwalkers have consciously committed crimes, including murder. In past decades individuals in Britain and Canada have been acquitted of murder after convincing juries that they were sleepwalking and unaware of what they were doing when they committed the acts.
Such cases, Kannape said, involve the idea of “an automatism that you did not do the act consciously -- an automatism that affects the intent to do something.” Further understanding of sleepwalkers’ state of awareness, he continued, could give juries more solid information on which to determine their verdicts.
Sleepwalking begins when the individual partly arouses from a deep sleep. Individuals can literally get up from their beds and walk, but have glassy expressions, fail to respond to others, and nearly always forget their actions once they wake up. Although killing while sleepwalking is highly unusual, activities can take uninhibited or complex forms, such as screaming out loud, eating voraciously, and even driving a vehicle.
Sleepwalkers have a complicated state of awareness. “They will wake up, but not entirely; they are partially awake and partially asleep,” Kannape explained. “During an episode, observations show, parts of the brain are still asleep and parts awake. Sleepwalkers have a very minimal consciousness.”
The condition occurs in roughly one-sixth of children, but most outgrow it by their teenage years. For adults who continue to sleepwalk, however, the activity can have severe consequences for themselves and others.
Studying sleepwalking isn’t easy, because scientists find it almost impossible to set up monitoring equipment in individuals’ bedrooms and then to remain patient enough to wait for an episode.
“Studies have to be done in a sleep lab, by monitoring EEGs and movement patterns,” Kannape said. “But the individual might sleep really well in the well-regulated environment.” Overcoming that problem by depriving subjects of sleep before studying them is both invasive and likely to produce atypical results.
Another alternative approach -- studying sleepwalkers when they are awake -- has typically failed to reveal any differences between them and non-sleepwalkers in simple tasks such as walking.
However, Kannape and Olaf Blanke, a neuroscientist at Switzerland’s École Polytechnique Fédérale de Lausanne, devised a more complex task for their subjects, using virtual reality.
The pair and their collaborators outfitted fully awake sleepwalkers and non-sleepwalkers with full-body motion capture suits in a room equipped with infrared tracking cameras. They report on their research this fall in the journal Current Biology.
First, the team asked the subjects to walk toward a virtual cylinder while watching life-sized avatars of themselves. To test their subjects’ awareness of their movements, the experimental team could change the avatars’ trajectories. Both sleepwalkers and non-sleepwalkers performed equally well in coping with those changes and continuing to walk towards the targets.
Team members then added a level of complexity. They asked their subjects to count out loud backward from 200 in increments of seven while walking. This is a challenging task. According to Kannape, some subjects in other studies have fallen off treadmills while trying to achieve it.
In this case, the multitasking exercise revealed significant differences. “We found that sleepwalkers continued to walk at the same speed, with the same precision as before, and were more aware of their movements than non-sleepwalkers,” Blanke said. The non-sleepwalkers slowed down noticeably when they started counting down.
The research provides important behavioral markers for identifying sleepwalkers while they are awake, such as this awareness of their movements even when distracted, Blanke added.
In addition to the possibility of diagnosing sleepwalking in awake patients, the experiment offers opportunities for relating sleep to neuroscience. “It opens up the entire field of cognitive studies to work with sleepwalkers,” Kannape concluded.
Editor's note (February 20, 2018): After publication, we discovered that Oliver Kannape's affiliation was listed incorrectly in the story. He is a lecturer in cognitive neuroscience at the University of Central Lancashire in England. We regret the error.