Sleepwalking is the result of a survival mechanism gone awry

Why do some enter into such an irrational and potentially harmful state during sleep?

Last night, most of us went to the safety and comfort of our beds before drifting off to a night’s sleep. For some, this was the last conscious action before an episode of sleepwalking. 


Recent research from Stanford University shows that up to 4 per cent of adults might have had such an experience. In fact, sleepwalking is on the rise, in part due to increased use of pharmacologically based sleep aids – notably Ambien. Often, the episodes are harmless. Take for example, Lee Hadwin, a Londoner whose professional artistic talent seems to be present and activated only while he sleeps.

Sometimes, of course, sleepwalking is dangerous. Somnambulists are in an irrational state during which they could harm themselves or others. Some extreme examples include the instance of the English teenager who in 2009 jumped eight metres out of her bedroom window, or the case of Kenneth Parks in Toronto, who in 1987 drove 23km and murdered his mother-in-law, all apparently while sleeping. Parks committed the act – if that’s the right word – despite an agreeable relationship with the victim and a lack of motive.

Why do some enter into such a potentially harmful state during sleep? One answer comes from studies suggesting that ‘sleepwalking’ might not be an appropriate term for what is going on; rather, primitive brain regions involved in emotional response (in the limbic system) and complex motor activity (within the cortex) remain in ‘active’ states that are difficult to distinguish from wakefulness. Such activity is characterised by ‘alpha wave’ patterns detected during electroencephalogram (EEG) recordings. At the same time, regions in the frontal cortex and hippocampus that control rationality and memory remain essentially dormant and unable to carry out their typical functions, manifesting a ‘delta wave’ pattern seen during classic sleep. It’s as though sleepwalking results when the brain doesn’t completely transition from sleep to wakefulness – it’s essentially stuck in a sleep-wake limbo.

‘The rational part of the brain is in a sleep-like state and does not exert its normal control over the limbic system and the motor system,’ explains the Italian neuroscientist Lino Nobili, a sleep researcher at Niguarda Hospital in Milan. ‘So behaviour is regulated by a kind of archaic survival system like the one that is activated during fight-or-flight.’

But why would our brains enter into such a mixed state, representative of neither wakefulness nor sleeping? We need a restful sleep – would it not be more beneficial if the brain went totally ‘comatose’ until that rest was achieved? When one considers our distant, pre-human ancestors, answers begin to take shape. For aeons, the safety provided by the spot where our predecessors chose to lay their heads for the night was, in many ways, compromised compared with the safety of our current bedroom spaces.

Other species employ such strategies as well. I’m reminded of a startling experience I had while hiking. As I was navigating the trail in the twilight, a deer jumped out from underneath the branches of a fallen tree and bolted off into the distance. I was amazed at how close I had come to it before it sprang into furious action – only a few metres. It likely had been asleep and, upon waking, realised the potential danger it was in. What struck me was how the deer seemed to be triggered for action, even while asleep. In fact, many animals can maintain brain activity required for survival during sleep. For example, frigate birds fly for days, even months, and maintain flight during sleep while travelling vast distances over an ocean.

The phenomenon is observed in humans too. On the first night in a new environment, research has shown, one hemisphere of our brain remains more active than the other during sleep – essentially maintaining a ‘vigilant mode’, able to respond to unfamiliar, potentially danger-signalling sounds.

Scientists now agree that bouts of localised wakeful-like activity in motor-related areas and the limbic system can occur without concurrent sleepwalking. In fact, these areas have been shown to have low arousal thresholds for activation. Surprisingly, despite their association with sleepwalking, these low thresholds have been considered an adaptive trait – a boon to survival. Throughout most of our extensive ancestry, this trait may have been selected for its survival value.  

‘During sleep, we can have an activation of the motor system, so although you are sleeping and not moving, the motor cortex can be in a wake-like state – ready to go,’ explains Nobili, who led the team that conducted the work. ‘If something really goes wrong and endangers you, you don’t need your frontal lobe’s rationality to escape. You need a motor system that is ready.’ In sleepwalking, however, this adaptive system has gone awry. ‘An external trigger that would normally produce a small arousal triggers a full-blown episode.’ 

Antonio Zadra, a professor of psychology at the University of Montreal in Canada, explains it like this: ‘Information is being filtered by your brain, which is still monitoring the background – what’s going on around the sleeper – and deciding what’s important. “Ok, so we are not going to wake up the sleeper” or “This is potentially threatening so we should.” But the process of going from sleep to wakefulness is, in sleepwalkers, dysfunctional, clearly.’

Despite evidence of localised activity during sleep in both human and non-human animal brains, sleepwalking is, among primates, apparently a uniquely human phenomenon. It stands to reason, therefore, that the selection pressure for this trait in our ancestors uniquely outweighed the cost.

Philip Jaekl

This article was originally published at Aeon and has been republished under Creative Commons.

Cambridge scientists create a successful "vaccine" against fake news

A large new study uses an online game to inoculate people against fake news.

University of Cambridge
Politics & Current Affairs
  • Researchers from the University of Cambridge use an online game to inoculate people against fake news.
  • The study sample included 15,000 players.
  • The scientists hope to use such tactics to protect whole societies against disinformation.
Keep reading Show less

Yale scientists restore brain function to 32 clinically dead pigs

Researchers hope the technology will further our understanding of the brain, but lawmakers may not be ready for the ethical challenges.

Still from John Stephenson's 1999 rendition of Animal Farm.
Surprising Science
  • Researchers at the Yale School of Medicine successfully restored some functions to pig brains that had been dead for hours.
  • They hope the technology will advance our understanding of the brain, potentially developing new treatments for debilitating diseases and disorders.
  • The research raises many ethical questions and puts to the test our current understanding of death.

The image of an undead brain coming back to live again is the stuff of science fiction. Not just any science fiction, specifically B-grade sci fi. What instantly springs to mind is the black-and-white horrors of films like Fiend Without a Face. Bad acting. Plastic monstrosities. Visible strings. And a spinal cord that, for some reason, is also a tentacle?

But like any good science fiction, it's only a matter of time before some manner of it seeps into our reality. This week's Nature published the findings of researchers who managed to restore function to pigs' brains that were clinically dead. At least, what we once thought of as dead.

What's dead may never die, it seems

The researchers did not hail from House Greyjoy — "What is dead may never die" — but came largely from the Yale School of Medicine. They connected 32 pig brains to a system called BrainEx. BrainEx is an artificial perfusion system — that is, a system that takes over the functions normally regulated by the organ. The pigs had been killed four hours earlier at a U.S. Department of Agriculture slaughterhouse; their brains completely removed from the skulls.

BrainEx pumped an experiment solution into the brain that essentially mimic blood flow. It brought oxygen and nutrients to the tissues, giving brain cells the resources to begin many normal functions. The cells began consuming and metabolizing sugars. The brains' immune systems kicked in. Neuron samples could carry an electrical signal. Some brain cells even responded to drugs.

The researchers have managed to keep some brains alive for up to 36 hours, and currently do not know if BrainEx can have sustained the brains longer. "It is conceivable we are just preventing the inevitable, and the brain won't be able to recover," said Nenad Sestan, Yale neuroscientist and the lead researcher.

As a control, other brains received either a fake solution or no solution at all. None revived brain activity and deteriorated as normal.

The researchers hope the technology can enhance our ability to study the brain and its cellular functions. One of the main avenues of such studies would be brain disorders and diseases. This could point the way to developing new of treatments for the likes of brain injuries, Alzheimer's, Huntington's, and neurodegenerative conditions.

"This is an extraordinary and very promising breakthrough for neuroscience. It immediately offers a much better model for studying the human brain, which is extraordinarily important, given the vast amount of human suffering from diseases of the mind [and] brain," Nita Farahany, the bioethicists at the Duke University School of Law who wrote the study's commentary, told National Geographic.

An ethical gray matter

Before anyone gets an Island of Dr. Moreau vibe, it's worth noting that the brains did not approach neural activity anywhere near consciousness.

The BrainEx solution contained chemicals that prevented neurons from firing. To be extra cautious, the researchers also monitored the brains for any such activity and were prepared to administer an anesthetic should they have seen signs of consciousness.

Even so, the research signals a massive debate to come regarding medical ethics and our definition of death.

Most countries define death, clinically speaking, as the irreversible loss of brain or circulatory function. This definition was already at odds with some folk- and value-centric understandings, but where do we go if it becomes possible to reverse clinical death with artificial perfusion?

"This is wild," Jonathan Moreno, a bioethicist at the University of Pennsylvania, told the New York Times. "If ever there was an issue that merited big public deliberation on the ethics of science and medicine, this is one."

One possible consequence involves organ donations. Some European countries require emergency responders to use a process that preserves organs when they cannot resuscitate a person. They continue to pump blood throughout the body, but use a "thoracic aortic occlusion balloon" to prevent that blood from reaching the brain.

The system is already controversial because it raises concerns about what caused the patient's death. But what happens when brain death becomes readily reversible? Stuart Younger, a bioethicist at Case Western Reserve University, told Nature that if BrainEx were to become widely available, it could shrink the pool of eligible donors.

"There's a potential conflict here between the interests of potential donors — who might not even be donors — and people who are waiting for organs," he said.

It will be a while before such experiments go anywhere near human subjects. A more immediate ethical question relates to how such experiments harm animal subjects.

Ethical review boards evaluate research protocols and can reject any that causes undue pain, suffering, or distress. Since dead animals feel no pain, suffer no trauma, they are typically approved as subjects. But how do such boards make a judgement regarding the suffering of a "cellularly active" brain? The distress of a partially alive brain?

The dilemma is unprecedented.

Setting new boundaries

Another science fiction story that comes to mind when discussing this story is, of course, Frankenstein. As Farahany told National Geographic: "It is definitely has [sic] a good science-fiction element to it, and it is restoring cellular function where we previously thought impossible. But to have Frankenstein, you need some degree of consciousness, some 'there' there. [The researchers] did not recover any form of consciousness in this study, and it is still unclear if we ever could. But we are one step closer to that possibility."

She's right. The researchers undertook their research for the betterment of humanity, and we may one day reap some unimaginable medical benefits from it. The ethical questions, however, remain as unsettling as the stories they remind us of.

5 facts you should know about the world’s refugees

Many governments do not report, or misreport, the numbers of refugees who enter their country.

David McNew/Getty Images
Politics & Current Affairs

Conflict, violence, persecution and human rights violations led to a record high of 70.8 million people being displaced by the end of 2018.

Keep reading Show less