Idiot Brain (2 page)

But here's the question: if moving is integral to our well-being and survival, and we've actually evolved sophisticated biological systems to ensure it happens as often and as easily as possible, why does it sometimes make us throw up? This is the phenomenon known as motion sickness or travel sickness. Sometimes, often apropos of nothing, being in transit makes us bring up our breakfast, lose our lunch, or eject some other more recent but non-alliterative meal.

It's the brain that's actually responsible for this, not the stomach or innards (despite how it may feel at the time). What possible reason could there be for our brains to conclude, in defiance of aeons of evolution, that going from A to B is a legitimate cause for vomiting? In actual fact, the brain isn't defying our evolved tendencies at all. It's the numerous systems and mechanisms we have to facilitate motion that are causing the problem. Motion sickness occurs only when you're traveling by artificial means—when you're in a vehicle. Here's why.

Humans have a sophisticated array of senses and neurological mechanisms that give rise to proprioception, the ability to sense how our body is currently arranged, and which parts are going where. Put your hand behind your back and you can still sense the hand, know where it is and what rude gesture it's making, without actually seeing it. That's proprioception.

There's also the vestibular system, found in our inner ear. It's a bunch of fluid-filled canals (meaning “bony tubes” in this context) to detect our balance and position. There's enough space in there for fluid to move about in response to gravity, and there are neurons throughout it that can detect the location and arrangement of the fluids, letting our brain know our current position and orientation. If the fluid is at the top of the tubes, this means we're upside-down, which probably isn't ideal and should be remedied as soon as possible.

Human motion (walking, running, even crawling or hopping) produces a very specific set of signals. There's the steady up–down rocking motion inherent in bipedal walking, the general velocity and the external forces such as the movement of air passing you and your shifting internal fluids that this produces. All of these are detected by proprioception and the vestibular system.

The image hitting our eyes is one of the outside world going by. The same image could be caused either by us moving or by us staying still and the outside world going past. At the most basic level, both are valid interpretations. How does the brain know which is right? It receives the visual information, couples it with the information from the fluid system in the ear and concludes “body is moving; this is normal,” and then goes back to thinking about sex or revenge or Pokemon, whatever it is you're into. Our eyes and inner
systems work together to explain what's going on.

Movement via a vehicle produces a different set of sensations. Cars don't have that signature rhythmical rocking motion that our brains associate with walking (unless your suspension is well and truly shot), and the same usually goes for planes, trains and ships. When you're being transported, you're not the one actually “doing” the moving; you're just sitting there doing something to pass the time, such as trying to stop yourself from throwing up. Your proprioception isn't producing all those clever signals for the brain to comprehend what's going on. No signals means you're not doing anything to the reptile brain, and this is reinforced by your eyes telling it you're not moving. But you
are
actually moving, and the aforementioned fluids in your ear, responding to the forces caused by high-speed movement and acceleration, are sending signals to the brain that are saying you are traveling, and quite fast at that.

What's happening now is that the brain is getting mixed signals from a precisely calibrated motion-detection system, and it is believed that this is what causes motion sickness. Our conscious brain can handle this conflicting information quite easily, but the deeper, more fundamental subconscious systems that regulate our bodies don't really know how to deal with internal problems like this, and they've no idea what could possibly be happening to cause the malfunction. In fact, as far as the reptile brain is concerned, there's only one likely answer: poison. In nature, that's the only likely thing that can so deeply affect our inner workings and cause them to get so confused.

Poison is bad, and if the brain thinks there's poison in the body, there's only one reasonable response: get rid of it,
activate the vomiting reflex, pronto. The more advanced brain regions may know better, but it takes a lot of effort to alter the actions of the fundamental regions once they're under way. They are “set in their ways” after all, almost by definition.

The phenomenon is still not totally understood at present. Why don't we get motion sickness all the time? Why do some people never suffer from it? There may well be many external or personal factors, such as the exact nature of the vehicle in which you are traveling, or some neurological predisposition to sensitivity to certain forms of movement, that contribute to occurrence of motion sickness, but this section sums up the most popular current theory. An alternative explanation is the “nystagmus hypothesis,”
³
which argues that the inadvertent stretching of the extra-ocular muscles (the ones that hold and move the eyes) due to motion stimulates the vagus nerve (one of the main nerves that control the face and head) in weird ways, leading to motion sickness. In either case, we get motion sickness because our brain gets easily confused and has a limited number of options when it comes to fixing potential problems, like a manager who's been promoted above his or her ability level and responds with buzzwords and crying fits when asked to do anything.

Seasickness seems to hit people the hardest. On land there are many items in the landscape to look at that reveal your movements (for instance, trees going past); on a ship there's usually just the sea and things that are too far away to be of any use, so the visual system is even more likely to assert that there's no movement happening. Traveling on the sea also adds an unpredictable up–down motion that gets the ear fluids firing off even more signals to an increasingly confused brain. In Spike Milligan's war memoir
Adolf Hitler: My
Part in His Downfall
, Spike was transferred to Africa by ship during World War II, and was one of the only soldiers in his squad who didn't succumb to seasickness. When asked what the best way to deal with seasickness was, his reply was simply, “Sit under a tree.” There's no supporting research available, but I'm fairly confident this method would work to prevent airsickness too.

Room for pudding?

(The brain's complex and confusing control of diet and eating)

Food is fuel. When your body needs energy, you eat. When it doesn't, you don't. It should be so simple when you think about it, but that's exactly the problem: us big smart humans can and do
think
about it, which introduces all manner of problems and neuroses.

The brain exerts a level of control over our eating and appetite that might surprise most people.
*
You'd think it's all controlled by the stomach or intestines, perhaps with input from the liver or fat reserves, the places where digested matter is processed and/or stored. And indeed, they do have their part to play, but they aren't as dominant as you might think.

Take the stomach; most people say they feel “full” when they've eaten enough. This is the first major space in the body in which consumed food ends up. The stomach expands as you fill it, and the nerves in the stomach send signals to the brain to suppress appetite and stop eating, which makes perfect sense. This is the mechanism exploited by those weight-loss milkshakes you drink instead of eating meals.
⁵
The milkshakes contain dense stuff that fills the stomach quickly, expanding it and sending the “I'm full” messages to the brain without you having to pack it with cake and pies.

They are, however, a short-term solution. Many people report feeling hungry less than 20 minutes after drinking one of these shakes, and that's largely because the stomach expansion signals are just one small part of the diet and appetite control. They're the bottom rung of a long ladder that goes all the way up to the more complex elements of the brain. And the ladder occasionally zigzags or even goes through loops on the way up.
⁶

It's not just the stomach nerves that influences our appetite; there are also hormones that play a role. Leptin is a hormone, secreted by fat cells, that decreases appetite. Ghrelin is released by the stomach, and increases appetite. If you have more fat stores, you secrete more appetite-suppressing hormone; if your stomach is noticing a persistent emptiness, it secretes hormone to increase appetite. Simple, right? Unfortunately, no. People may have increased levels of these
hormones depending on their food requirements, but the brain can quickly grow used to them and effectively ignores them if they persist too long. One of the brain's more prominent skills is the ability to ignore anything that becomes too predictable, no matter how important it may be (this is why soldiers can still get some sleep in war zones).

Have you noticed how you always have “room for dessert”? You might have just eaten the best part of a cow, or enough cheesy pasta to sink a gondola, but you can manage that fudge brownie or triple-scoop ice-cream sundae. Why?
How?
If your stomach is full, how is eating more even physically possible? It's largely because your brain makes an executive decision and decides that, no, you still have room. The sweetness of desserts is a palpable reward that the brain recognizes and wants (see
Chapter 8
) so it overrules the stomach, saying, “No room in here.” Unlike the situation with motion sickness, here the neocortex overrules the reptile brain.

Exactly why this is the case is uncertain. It may be that humans
need
quite a complex diet in order to remain in tip-top condition, so rather than just relying on our basic metabolic systems to eat whatever is available, the brain steps in and tries to regulate our diet better. And this would be fine if that was all the brain does. But it doesn't. So it isn't.

Learned associations are incredibly powerful when it comes to eating. You may be a big fan of something like, say, cake. You can be eating cake for years without any bother, then one day you eat some cake that makes you vomit. Could be some of the cream in it has gone sour; it might contain an ingredient you're allergic to; or (and here's the annoying one)
it could be that something else entirely made you throw up shortly after eating cake
. But, from then on, your brain has made
the connection and considers cake out of bounds; if you even look at it again it can trigger the nausea response. The disgust association is a particularly powerful one, evolved to stop us eating poison or diseased things, and it can be a hard one to break. No matter that your body has consumed it dozens of times with no problem; the brain says,
No!
And there's little you can do about it.

But it doesn't have to be anything as extreme as throwing up. The brain interferes with almost every food-based decision. You may have heard that the first bite is with the eye? Much of our brain, as much as 65 percent of it, is associated with vision rather than taste.
⁷
While the nature and function of the connections is staggeringly varied, it does reveal that vision is clearly the go-to sensory information for the human brain. By contrast, taste is almost embarrassingly feeble, as we shall see in
Chapter 5
. If blindfolded while wearing nose plugs, your typical person can often mistake potato for apple.
⁸
Clearly, the eyes have a much greater influence over what we perceive than the tongue, so how food looks is going to influence strongly how we enjoy it, hence all the effort on presentation in the fancy eateries.

Routine can also drastically influence your eating habits. To demonstrate this, consider the phrase “lunchtime.” When is lunchtime? Most will say between 12 p.m. and 2 p.m. Why? If food is needed for energy, why would everyone in a population, from hard physical workers like laborers and lumberjacks to sedentary people like writers and programmers, eat lunch at the same time? It's because we all agreed long ago that this was lunchtime and people rarely question it. Once you fall into this pattern, your brain quickly expects it to be maintained, and you'll get hungry
because it's time to eat
,
rather than
knowing it's time to eat
because you're hungry. The brain apparently thinks logic is a precious resource to be used only sparingly.

Habits are a big part of our eating regime, and once our brain starts to expect things, our body quickly follows suit. It's all very well saying to someone who's overweight that they just need to be more disciplined and eat less, but it's not that easy. How you ended up overeating in the first place can be due to many factors, such as comfort eating. If you're sad or depressed, your brain is sending signals to the body that you're tired and exhausted. And if you're tired and exhausted, what do you need? Energy. And where do you get energy?
Food!
High-calorie food can also trigger the reward and pleasure circuits in our brains.
⁹
This is also why you rarely ever hear of a “comfort salad.”

But once your brain and body adapt to a certain caloric intake, it can be very hard to reduce it. You've seen sprinters or marathon runners after a race, doubled up and gasping for breath? Do you ever consider them gluttons for oxygen? You never see anyone tell them they're lacking in discipline and are just being lazy or greedy. It's a similar effect (albeit a less healthy one) with eating, in that the body changes to expect the increased food intake, and as a result it becomes harder to stop. The exact reasons why someone ends up eating more than they need in the first place and becoming accustomed to it are impossible to determine as there are so many possibilities, but you could argue that it's an inevitability when you make endless amounts of food available to a species that has evolved to take whatever food it can get whenever it can get it.