by Dean Burnett
This terror is not unrelated either; the helplessness and vulnerability of sleep paralysis triggers a powerful fear response. This mechanism of this will be discussed in the next section, but it can be intense enough to trigger hallucinations of danger, giving rise to feelings of another presence in the room, and this is believed to be the root cause of alien-abduction fantasies, and the legend of the succubus. Most people who experience sleep paralysis do so only briefly and very rarely, but in some it can be a chronic and persistent concern. It has been linked to depression and similar disorders, suggesting some underlying issue with brain processing.
Even more complex, but likely to be related to sleep paralysis, is the occurrence of sleepwalking. This has also been traced to the system that shuts off motor control of the brain during sleep, except now it’s the reverse – that the system isn’t powerful or coordinated enough. Sleepwalking is more common in children, leading scientists to theorise sleepwalking is due to the motor inhibition system being not yet fully developed. Some studies point to hints of underdevelopment in the central nervous system as a likely cause (or at least contributing factor).19 Sleepwalking has been observed as heritable and more common in certain families, suggesting that a genetic component might underlie this central nervous system immaturity. But sleepwalking can also occur in adults under the influence of stress, alcohol, medications and so forth, any or all of which might also affect this motor inhibition system. Some scientists argue that sleepwalking is a variation or expression of epilepsy, which of course is the result of uncontrolled or chaotic brain activity, which seems logical in this instance. However it’s expressed, it’s invariably alarming when the brain gets the sleep and motor control functions mixed up.
But this wouldn’t be an issue if the brain wasn’t so active during sleep to begin with. So why is it? What’s it doing in there?
The highly active REM sleep stage has a number of possible roles. One of the main ones involves memory. One persistent theory is that during REM sleep the brain is reinforcing and organising and maintaining our memories. Old memories are connected to new memories; new memories are activated to help reinforce them and make them more accessible; very old memories are stimulated to make sure the connections to them aren’t lost entirely, and so on. This process takes place during sleep, possibly because there is no external information coming in to the brain to confuse or complicate matters. You never come across roads being resurfaced while cars are still going over them, and the same logic applies here.
But the activation and maintenance of the memories causes them to be effectively ‘relived’. Very old experiences and more recent imaginings are all thrown into the mix together. There’s no specific order or logical structure to the sequence of experiences this results in, hence dreams are invariably so other-worldly and bizarre. It’s also theorised that the frontal regions of the brain responsible for attention and logic are trying to impose some sort of rationale on this ramshackle sequences of events, which explains why we still feel as if dreams are real while they’re happening and the impossible occurrences don’t strike as unusual at the time.
Despite the wild and unpredictable nature of dreams, certain dreams can be recurring, and these are usually associated with some issue or problem. Indeed, if there’s a certain thing in your life stressing you out (like a deadline for finishing a book you’ve agreed to write) then you’re going to think about this a lot. As a result, you’ll have a lot of new memories about it that need to be organised, so will occur more in dreams, so it crops up more often and you end up regularly dreaming about burning down a publisher’s office.
Another theory about REM sleep is that it’s especially important for small children as it aids neurological development, going beyond just memories and shoring up and reinforcing all the connections in the brain. This would help explain why babies and the very young have to sleep a lot more than adults (often more than half the day) and spend a great deal longer in REM sleep (about 80 per cent of total sleep time as opposed to about 20 per cent in adults). Adults retain REM sleep but at lower levels to keep the brain efficient.
Yet another theory is that sleep is essential to clear out the waste products of the brain. The ongoing complex cellular processes of the brain produce a wide variety of by-products that need to be cleared away, and studies have shown that this occurs at a higher rate during sleep, so it could be that sleep for the brain is the equivalent of a restaurant closing down to clear up between lunchtime and evening openings; it’s just as busy, but doing different things.
Whatever the true reason for it, sleep is essential for normal brain functioning. People deprived of sleep, particularly of REM sleep, quickly show a serious decline in cognitive focus, attention and problem-solving skills, an increase in stress levels, lower moods, irritability, and a drop in all-round task performance; the nuclear disasters of Chernobyl and Three Mile Island have been linked to overworked and exhausted engineers, so has the Challenger shuttle disaster, and let’s not go into the long-term consequences of decisions made by sleep-deprived doctors on their third successive twelve-hour shift in two days.20 If you go too long without sleep, your brain starts initiating ‘micro sleeps’, where you grab snatches of sleep for minutes or even seconds at a time. But we’ve evolved to expect and utilise long periods of unconsciousness, and we can’t really make do with small crumbs here and there. Even if we do manage to persevere with all the cognitive problems a lack of sleep causes, it’s associated with impaired immune systems, obesity, stress and heart problems.
So if you happen to nod off while reading this book, it’s not boring, it’s medicinal.
It’s either an old dressing gown or a bloodthirsty axe murderer
(The brain and the fight-or-flight response)
As living, breathing humans, our survival depends on our biological requirements – sleeping, eating, moving – being met. But these aren’t the only things essential to our existence. There are plenty of dangers lurking in the wider world, just waiting for the opportunity to snuff us out. Luckily, millions of years of evolution have equipped us with a sophisticated and reliable system of defensive measures in order to respond to any potential threat, coordinated with admirable speed and efficiency by our marvellous brains. We even have an emotion dedicated to recognising and focusing on threats: fear. One down side of this is that our brains have an inherent ‘better safe than sorry’ approach that means we regularly experience fear in situations where it’s not really warranted.
Most people can relate to this. Maybe you were lying awake in a dark bedroom when the shadows on the walls started looking less like the branches of the dead tree outside and more like the outstretched skeletal arms of some hideous monster. Then you see the hooded figure by the door.
It’s clearly the axe murderer your friend told you about. So, obviously, you collapse into a terrified panic. The axe murderer doesn’t move though. He can’t. Because he’s not an axe murderer, he’s a dressing-gown. The one you hung up on the bedroom door earlier.
It makes no logical sense, so why on earth do we have such powerful fear reactions to things that are clearly utterly harmless? Our brains, however, aren’t convinced of this harmlessness. We could all live in sterilised bubbles with every sharp edge smoothed down, but as far as the brain is concerned death could come leaping out of the nearest bush at any point. To our brains, daily life is like tightrope-walking over a vast pit full of furious honey badgers and broken glass; one wrong move and you’ll end up as a gruesome mess in temporary but exquisite pain.
Such a tendency is understandable. Humans evolved in a hostile, wild environment with dangers at every turn. Those humans who developed a healthy paranoia and jumped at shadows (that genuinely may have had teeth) survived long enough to pass on their genes. As a result, when presented with any conceivable threat or danger, the modern human has a suite of (mostly unconscious) response mechanisms providing a reflex that enable them to deal better with said threat, and this reflex is sti
ll very much alive and kicking (as are humans, thanks to it). This reflex is the fight-or-flight response, which is a great name as it concisely but accurately describes its function. When presented with a threat, people can either fight it or run away.
The fight-or-flight response starts in the brain, as you’d expect. Information from the senses reaches the brain and enters the thalamus, which is basically a central hub for the brain. If the brain were a city, the thalamus would be like the main station where everything arrives before being sent to where it needs to be.21 The thalamus connects to both the advanced conscious parts of the brain in the cortex and the more primitive ‘reptile’ regions in the midbrain and brainstem. It’s an important area.
Sometimes the sensory information that reaches the thalamus is worrying. It might be unfamiliar, or familiar but worrying in context. If you’re lost in the woods and you hear a growl, that’s unfamiliar. If you’re home alone and you hear footsteps upstairs, that’s familiar, but in a bad way. In either case, the sensory information reporting this is tagged ‘This isn’t good.’ In the cortex, where it’s processed further, the more analytical part of the brain looks at the information and wonders ‘Is this something to worry about?’ while checking the memory to see if anything similar has occurred before. If there’s not enough information to determine that whatever we’re experiencing is safe, it can trigger the fight-or-flight response.
However, as well as the cortex, the sensory information is relayed to the amygdala, the part of the brain responsible for strong emotional processing, and fear in particular. The amygdala doesn’t do subtlety; it senses something might be amiss and initiates a red alert straight away, a response far faster than the more complex analysis in the cortex could ever hope to be. This is why a scary sensation, like a balloon popping unexpectedly, produces a fear response almost instantly, before you can process it enough to realise it’s harmless.22
The hypothalamus is then signalled. This is the region right under the thalamus (hence the name), and is largely responsible for ‘making things happen’ in the body. To extend my earlier metaphor, if the thalamus is the station, the hypothalamus is the taxi rank outside it, taking important things into the city where they get stuff done. One of the roles of the hypothalamus is triggering the fight-or-flight response. It does this by getting the sympathetic nervous system to put the body effectively at ‘battle stations’.
At this point you may be wondering, ‘What’s the sympathetic nervous system?’ Good question.
The nervous system, the network of nerves and neurons spread throughout the body, allows the brain to control the body and the body to communicate with and influence the brain. The central nervous system – the brain and the spinal cord – is where the big decisions are made, and as such these areas are protected by a sturdy layer of bone (the skull and the spinal column). But many major nerves branch out from these structures, dividing and spreading further until they innervate (the actual term for supplying organs and tissue with nerves) the rest of the body. These far-reaching nerves and branches, outside the brain and spinal cord, are referred to as the peripheral nervous system.
The peripheral nervous system has two components. There’s the somatic nervous system, also known as the voluntary nervous system, which links the brain to our musculoskeletal system to allow conscious movement. There’s also the autonomic nervous system, which controls all the unconscious processes that keep us functioning, so is largely linked to internal organs.
But, just to make it more complicated, the autonomic nervous system also has two components: the sympathetic and parasympathetic nervous systems. The parasympathetic nervous system is responsible for maintaining the more calm processes of the body, such as gradual digestion after meals or regulating the expulsion of waste. If someone were to make a sitcom starring the different parts of the human body, the parasympathetic nervous system would be the laidback character, telling people to ‘chill out’ while rarely getting off the couch.
In contrast, the sympathetic nervous system is incredibly highly strung. It would be the twitchy paranoid one, constantly wrapping itself in tin foil and ranting about the CIA to anyone who’ll listen. The sympathetic nervous system is often labelled the fight-or-flight system because it’s what causes the various responses the body employs to deal with threats. The sympathetic nervous system dilates our pupils, to ensure more light enters our eyes so we can better spot dangers. It increases the heart rate while shunting blood away from peripheral areas and non-essential organs and systems (including digestion and salivation – hence the dry mouth when we’re scared) and towards the muscles, to ensure that we have as much energy as possible for running or fighting (and feel quite tense as a result).
The sympathetic system and parasympathetic systems are constantly active and usually balance each other and ensure normal functioning of our bodily systems. But in times of emergency, the sympathetic nervous system takes over and adapts the body for fighting or (metaphorical) flying. The fight-or-flight response triggers the adrenal medulla (just above the kidneys) as well, meaning our bodies are flooded with adrenalin, which produces many more of the familiar responses to a threat: tension, butterflies in the stomach, rapid breathing for oxygenation, even relaxing of the bowels (you don’t want to be carrying unnecessary ‘weight’ while running for your life).
Our awareness is also turned up, making us extra sensitive to potential dangers, reducing our ability to concentrate on any minor issues we were dealing with before the scary thing happened. This is the result of both the brain being alert to danger anyway and by the adrenalin suddenly hitting it, enhancing some forms of activity and limiting others.23
The brain’s emotional processing also steps up a gear,24 largely because the amygdala is involved. If we’re dealing with a threat, we need to be motivated to take it on or get away from it asap, so we rapidly become intensely fearful or angry, providing further focus and ensuring we don’t waste time with tedious ‘reasoning’.
When faced with a potential threat, both brain and body rapidly shift to a state of enhanced awareness and physical readiness to deal with it. But the problem with this is the ‘potential’ aspect. The fight-or-flight response kicks in before we know whether it’s actually needed.
Again, this makes logical sense; the primitive human who runs from something that might be a tiger was more likely to survive and reproduce than the one who said, ‘Let’s just wait so we can be sure.’ The first human arrives back at the tribe intact, whereas the second is the tiger’s breakfast.
This is a useful survival strategy in the wild but for the modern human it’s quite disruptive. The fight-or-flight response involves many real and demanding physical processes, and it takes time for the effects of these to wear off. The adrenalin surge alone takes a while to leave the bloodstream, so having our whole bodies enter combat mode whenever a balloon pops unexpectedly is rather inconvenient.25 We can experience all the tension and build-up required for a fight-or-flight response, only to realise quickly that it’s not required. But we still have tense muscles and a rapid heartbeat and so on, and not relieving this with a frantic sprint or wrestling session with an intruder can cause cramps, knots in muscles, trembling and many other unpleasant consequences as the tension becomes too much.
There’s also the increased emotional sensation. Someone primed to be terrified or angry can’t just switch it off in an instant, so it often ends up being directed at less deserving targets. Tell an incredibly tense person to ‘relax’ and see what happens.
The demanding physical aspect of the fight-or-flight response is only part of the issue. The brain being so attuned to seek out and focus on danger and threats is increasingly problematic. Firstly, the brain can take account of the present situation and become more alert to danger. If we’re in a darkened bedroom, the brain is aware that we can’t see as much, so is attuned for any suspicious noise, and we know it should be quiet at night, so any noises that do occur get far more attention and are mo
re likely to trigger our alarm systems. Also, our brain’s complexity means humans now have the ability to anticipate, rationalise and imagine, meaning we can now be scared of things that haven’t happened or aren’t there such as the axe-murderer dressing-gown.
Chapter 3 is dedicated to the weird ways in which the brain uses and processes fear in our daily lives. When not overseeing (and often disrupting) the fundamental processes we need to keep ourselves alive, our conscious brains are exceptionally good at thinking up ways in which we might come to harm. And it doesn’t even have to be physical harm; it can be intangible things such as embarrassment or sadness, things that are physically harmless but that we still really want to avoid, so the mere possibility is enough to set off our fight-or-flight response.
Notes
1 S. B. Chapman et al., ‘Shorter term aerobic exercise improves brain, cognition, and cardiovascular fitness in aging’, Frontiers in Aging Neuroscience, 2013, vol. 5
2 V. Dietz, ‘Spinal cord pattern generators for locomotion’, Clinical Neurophysiology, 2003, 114(8), pp. 1379–89
