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 organizing 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 into 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 theorized 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 us 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 organized, 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 percent of total sleep time as opposed to about 20 percent 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 utilize 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 bathrobe 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 marvelous brains. We even have an emotion dedicated to recognizing 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 are lying awake in a dark bedroom when the shadows on the walls start 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 bathrobe. 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 sterilized 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.