Idiot Brain (3 page)

And if you need any further proof that the brain controls
eating, consider the existence of eating disorders such as anorexia or bulimia. The brain manages to convince the body that body image is more important than food, so
it doesn't need food!
This is akin to you convincing a car that it doesn't need gasoline. It's neither logical nor safe, and yet it happens worryingly regularly. Moving and eating, two basic requirements, are made needlessly complex due to our brains interfering with the process. However, eating is one of life's great pleasures, and if we were to treat it as if we were just shoveling coal into a furnace, maybe our lives would be a lot duller. Maybe the brain knows what it's doing after all.

To sleep, perchance to dream . . . or spasm, or suffocate, or sleepwalk

(The brain and the complicated properties of sleep)

Sleep involves doing literally nothing, lying down and not being conscious. How complicated could it possibly be?

Very. Sleep, the actual workings of sleep, how it happens and what's going on during it, is something people don't really think about that often. Logically, it's very hard to think about sleep while it's happening, what with the whole “being unconscious” thing. This is a shame because it's baffled many scientists, and if more people thought about it we might be able to figure it out faster.

To clarify; we
still
don't know
the purpose of sleep! It's been observed (if you adopt a fairly loose definition) in almost every other type of animal, even the simplest kinds like nematodes,
a basic and common parasitic flatworm.
¹⁰
Some animals, such as jellyfish and sponges, don't show any sign of sleeping, but they don't even have brains so you can't trust them to do much of anything. But sleep, or at least some regular period of inactivity, is seen in a wide variety of radically different species. Clearly it's important, with deep evolutionary origins. Aquatic mammals have evolved methods of sleeping with only half the brain at a time because if they slept fully they'd stop swimming, sink and drown. Sleep is so important it outranks “not drowning,” and yet we don't know why.

There are many existing theories, such as healing. Rats deprived of sleep have been shown to recover much more slowly from wounds and generally don't live nearly as long as rats that get sufficient sleep.
¹¹
An alternative theory is that sleep reduces the signal strength of weak neurological connections to make them easier to remove.
¹²
Another is that sleep facilitates reduction of negative emotions.
¹³

One of the more bizarre theories is that sleep evolved as a means of preserving us from predators.
¹⁴
A lot of predators are active at night, and humans don't need 24 hours of activity to sustain themselves, so sleep provides prolonged periods where people are essentially inert, and not giving off the signs and cues that a nocturnal predator could use to find them.

Some may scoff at the cluelessness of modern scientists. Sleep is for rest, where we give our body and brain time to recover and recharge after a day's exertions. And, yes, if we've been doing something particularly exhausting, a prolonged period of inactivity is helpful for letting our systems recover and replenish/rebuild where necessary.

But if sleep is all about resting, why do we almost always sleep
for the same length of time
whether we've spent the day
hauling bricks or sitting in our pajamas watching cartoons? Surely, both activities don't require equivalent recuperation time. And metabolic activity of the body during sleep lowers by only 5 percent to 10 percent. This is only slightly “relaxing”— like dropping from 50 mph to 45 mph while driving because there's smoke coming from the engine is only slightly helpful.

Exhaustion doesn't dictate our sleep patterns, which is why people seldom just fall asleep while running a marathon. Rather, the timing and duration of sleep is determined by our body's circadian rhythms, set by specific internal mechanisms. There's the pineal gland in the brain that regulates our sleep pattern via secretion of the hormone known as melatonin, which makes us relaxed and sleepy. The pineal gland responds to light levels. The retinas in our eyes detect light and send signals to the pineal gland, and the more signals it receives the less melatonin it releases (although it does still produce it at lower levels). The melatonin levels in our body rise gradually throughout the day, and increase more rapidly when the sun goes down, hence our circadian rhythms are linked to daylight hours so we're usually alert in the morning and tired at night.

This is the mechanism behind jet-lag. Traveling to another time zone means you are experiencing a completely different schedule of daylight, so you may be experiencing 11 a.m. levels of daylight when your brain thinks it's 8 p.m. Our sleep cycles are very precisely attuned, and this throwing off of our melatonin levels disrupts them. And it's harder to “catch up” on sleep than you'd think; your brain and body are tied to the circadian rhythm, so it's difficult to force sleep at a time when it's not expected (although not impossible). A few days of the new light schedule and the rhythms are effectively reset.

You might wonder, if our sleep cycle is so sensitive to light levels, why doesn't artificial light affect them? Well, it does. People's sleep patterns now have apparently changed wildly in the last few centuries since artificial light became commonplace, and sleep patterns differ depending on culture.
¹⁵
Cultures with less access to artificial light or different daylight patterns (for example, at higher latitudes) have sleep patterns that have adapted to their circumstances.

Our core body temperature also changes according to similar rhythms, varying between 98.6°F and 96.8°F (which is a big variation for a mammal). It's highest in the afternoon, then drops as evening approaches. At midway between the highest and lowest points is when we typically go to bed, so we're asleep when it's at its lowest, which may explain the human tendency to insulate ourselves with blankets while we sleep; we're colder then than when we're awake.

To challenge further the assumption that sleep is all about rest and conserving energy, sleep has been observed in hibernating animals.
¹⁶
That is, in animals that are
already unconscious
. Hibernation isn't the same as sleep; the metabolism and body temperature drop much lower; it lasts longer; it's closer to a coma really. But hibernating animals regularly enter a sleep state, so they
use more energy in order to fall asleep!
This idea that sleep is about rest is clearly not the whole story.

This is especially true of the brain, which demonstrates complicated behaviors during sleep. Briefly, there are currently four stages of sleep: rapid-eye-movement sleep (REM) and three non-rapid-eye-movement (NREM) stages (NREM Stage 1, NREM Stage 2 and NREM Stage 3, in a rare example of neuroscientists keeping things simple for the lay person). The three NREM stages are differentiated
by the type of activity the brain displays during each.

Often the different areas in the brain synchronize their patterns of activity, resulting in what you might call “brainwaves.” If other people's brains start synchronizing too, this is called a “Mexican brainwave.”
^†
There are several types of brainwaves, and each NREM stage has specific ones that occur.

In NREM Stage 1 the brain displays largely “alpha” waves; NREM Stage 2 has weird patterns called “spindles,” and NREM Stage 3 is predominately “delta” waves. There is a gradual reduction in brain activity as we progress through the sleep stages, and the further you progress the harder you are to wake up. During NREM Stage 3 sleep—“deep” sleep—an individual is far less responsive to external stimulus such as someone yelling, “Wake up! The house is on fire!,” than at Stage 1. But the brain never shuts down completely, partly because it has several roles in maintaining the sleep state, but mostly because if it did shut down completely we'd be dead.

Then we have REM sleep, where the brain is as active, if not more so, as when we're awake and alert. One interesting (or sometimes terrifying) feature of REM sleep is REM atonia. This is where the brain's ability to control movement via motor neurons is essentially switched off, leaving us unable to move. Exactly how this happens is unclear; it could be that specific neurons inhibit activity in the motor cortex, or the sensitivity of the motor control areas is reduced, making it much harder to trigger movements. Regardless of how it occurs, it does.

And that's a good thing, too. REM sleep is when dreaming occurs, so if the motor system was left fully operational
people would be physically acting out what they're doing in their dreams. If you can remember anything you've done in your dreams, you can probably see why this would be something you'd want to avoid. Thrashing and flailing while asleep and unaware of your surroundings is potentially very dangerous, for you and any unfortunate person sleeping nearby. Of course, the brain isn't 100 percent reliable, so there are cases of REM behavioral disorders, where the motor paralysis isn't effective and people do in fact act out their dreams. And it's as hazardous as I've suggested, resulting in phenomena such as sleepwalking, which we'll get to shortly.

There are also more subtle glitches which will probably be more familiar to the everyday person. There's the hypnic jerk, where you twitch suddenly and unexpectedly while falling asleep. It feels as if you're falling suddenly, resulting in spasm while in bed. This occurs more in children and gradually declines as we age. The occurrence of hypnic jerks has been associated with anxiety, stress, sleep disorders and so on, but overall they seem to be largely random. Some theories state it's the brain mistaking falling asleep for dying, so it tries urgently to wake us up. But this makes little sense as the brain needs to be complicit in us falling asleep. Another theory is that it's an evolutionary holdover from a time when we slept in trees and sudden tilting or tipping sensations meant we were about to fall out, so the brain panics and wakes us. It could even be something else entirely. The reason it occurs more in children is likely to be due to the brain still being in the developing stages, where connections are still being wired up and processes and functions are being ironed out. In many ways we never truly get rid of
all
the glitches and kinks in such complicated systems as those used by our brains, so hypnic jerks persist into
adulthood. Overall it's just a bit odd, if essentially harmless.
¹⁷

What's also mostly harmless, but doesn't feel like it, is sleep paralysis. For some reason, the brain sometimes forgets to switch the motor system back on when we regain consciousness. Exactly how and why this happens hasn't been confirmed, but the dominant theories link it to disruption of the neat organization of the sleep states. Each stage of sleep is regulated by different types of neuronal activity, and these are regulated by different sets of neurons. It can happen that the differing activity doesn't alter smoothly, so the neuronal signals that reactivate the motor system are too weak, or the ones that shut it down are too strong or last too long, and as such we regain consciousness without regaining motor control. Whatever it is that shuts down movement during REM sleep is still in place when we become fully alert, so we're unable to move.
¹⁸
This typically doesn't last long, as once we wake up the rest of the brain activity resumes normal conscious levels and overrides the sleep system signals, but while it does it can be terrifying.

This terror is not unrelated either; the helplessness and vulnerability of sleep paralysis triggers a powerful fear response. The 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 theorize 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 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.