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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.
This article was originally published at Aeon and has been republished under Creative Commons.
The idea of 'absolute time' is an illusion. Physics and subjective experience reveal why.
- Since Einstein posited his theory of general relativity, we've understood that gravity has the power to warp space and time.
- This "time dilation" effect occurs even at small levels.
- Outside of physics, we experience distortions in how we perceive time — sometimes to a startling extent.
Physics without time<p>In his book "The Order of Time," Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.</p><p style="margin-left: 20px;">"If I observe the microscopic state of things," writes Rovelli, "then the difference between past and future vanishes … in the elementary grammar of things, there is no distinction between 'cause' and 'effect.'"</p><p>So, why do we perceive time as flowing <em>forward</em>? Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.</p><p>Rovelli says key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. This is a one-way street. For example, an ice cube melts into a hot cup of tea, never the reverse. Rovelli suggests a similar phenomenon might explain why we're only able to perceive the past and not the future.</p><p style="margin-left: 20px;">"Any time the future is definitely distinguishable from the past, there is something like heat involved," Rovelli wrote for the <a href="https://www.ft.com/content/ce6ef7b8-429a-11e8-93cf-67ac3a6482fd" target="_blank"><em>Financial Times</em></a>. "Thermodynamics traces the direction of time to something called the 'low entropy of the past', a still mysterious phenomenon on which discussions rage."</p>
The strange subjectivity of time<p>Time moves differently atop a mountain than it does on a beach. But you don't need to travel any distance at all to experience strange distortions in your perception of time. In moments of life-or-death fear, for example, your brain would release large amounts of adrenaline, which would speed up your internal clock, causing you to perceive the outside world as moving slowly.<br></p><p>Another common distortion occurs when we focus our attention in particular ways.</p><p style="margin-left: 20px;">"If you're thinking about how time is <em>currently</em> passing by, the biggest factor influencing your time perception is attention," Aaron Sackett, associate professor of marketing at the University of St. Thomas, told <em><a href="https://gizmodo.com/why-does-time-slow-down-and-speed-up-1840133782" target="_blank">Gizmodo</a></em>.<em> "</em>The more attention you give to the passage of time, the slower it tends to go. As you become distracted from time's passing—perhaps by something interesting happening nearby, or a good daydreaming session—you're more likely to lose track of time, giving you the feeling that it's slipping by more quickly than before. "Time flies when you're having fun," they say, but really, it's more like "time flies when you're thinking about other things." That's why time will also often fly by when you're definitely <em>not</em> having fun—like when you're having a heated argument or are terrified about an upcoming presentation."</p><p>One of the most mysterious ways people experience time-perception distortions is through psychedelic drugs. In an interview with <a href="https://www.theguardian.com/books/2018/apr/14/carlo-rovelli-exploding-commonsense-notions-order-of-time-interview" target="_blank"><em>The Guardian</em></a>, Rovelli described a time he experimented with LSD.</p><p style="margin-left: 20px;">"It was an extraordinarily strong experience that touched me also intellectually," he said. "Among the strange phenomena was the sense of time stopping. Things were happening in my mind but the clock was not going ahead; the flow of time was not passing any more. It was a total subversion of the structure of reality."<br></p><p>It seems few scientists or philosophers believe time is completely an illusion.</p><p style="margin-left: 20px;">"What we call <em>time</em> is a rich, stratified concept; it has many layers," Rovelli told <em><a href="https://physicstoday.scitation.org/do/10.1063/PT.6.4.20190219a/full/" target="_blank">Physics Today</a>.</em> "Some of time's layers apply only at limited scales within limited domains. This does not make them illusions."</p>What <em>is</em> an illusion is the idea that time flows at an absolute rate. The river of time might be flowing forever forward, but it moves at different speeds, between people, and even within your own mind.
The world's 10 most affected countries are spending up to 59% of their GDP on the effects of violence.
- Conflict and violence cost the world more than $14 trillion a year.
- That's the equivalent of $5 a day for every person on the planet.
- Research shows that peace brings prosperity, lower inflation and more jobs.
- Just a 2% reduction in conflict would free up as much money as the global aid budget.
- Report urges governments to improve peacefulness, especially amid COVID-19.
The lush biodiversity of South America's rainforests is rooted in one of the most cataclysmic events that ever struck Earth.
- One especially mysterious thing about the asteroid impact, which killed the dinosaurs, is how it transformed Earth's tropical rainforests.
- A recent study analyzed ancient fossils collected in modern-day Colombia to determine how tropical rainforests changed after the bolide impact.
- The results highlight how nature is able to recover from cataclysmic events, though it may take millions of years.