The Ravenous Brain: How the New Science of Consciousness Explains Our Insatiable Search for Meaning (14 page)

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Authors: Daniel Bor

BOOK: The Ravenous Brain: How the New Science of Consciousness Explains Our Insatiable Search for Meaning
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The simplest benefit an animal gains from a nervous system is the regulation of its basic states (homeostasis). This computer in the head is able, in almost every animal, to help control important biological features. By monitoring the animal’s internal temperature, for example, and initiating any needed response when the animal becomes too hot or too cold, it can keep this temperature within the optimal range, acting just like a thermostat. Even in cold-blooded animals, where temperature is regulated entirely by the ambient heat, this can be achieved by directing the animal to move into a hotter, less shaded region if it is too cold. This single regulatory process provides a powerful advantage for many animals over non-animals—namely, that they can exist in a wide variety of locations, and may not need to shut down for winter. When you have a computer around, you can also fine-tune many other features, such as how much energy (glucose) or water there is in the blood, the concentration of salt, and so on. In each case, there is a monitoring system and, if necessary, a chemical messenger (a hormone, usually) that cause a change to correct any form of imbalance.
But this internal regulation is only a tiny portion of what an animal brain does. The main purpose of a brain is to sense the outside world and move around based on this data. Retrieving accurate external information confers a significant potential survival advantage. Although some bacteria, with incredibly crude sensory skills, can detect via protein switches when food is scarce, which is indeed very clever, such an organism would look remarkably stupid if food was actually at the center of its world, but undetectable by it just because it was hidden by a chemical barrier. An animal with multiple senses might be able to look for food, immediately see exactly where it was, what it was, whether other animals were feasting on it, smell how energy rich it was, and hear if there were any predators nearby waiting to pounce as soon as the animal tucked in.
We take our senses so much for granted, and rarely perceive them for what they really are. Our senses are nothing more than conduits to pick up physical information about the environment: a small portion of the electromagnetic spectrum for vision, for instance, which almost everything around us reflects or even emits; the compression waves of air or water for sound, which many moving things generate; and chemical offshoots of interesting objects for smell. Our different senses feel utterly distinct to us, but there is an important bottom line here:
It’s all just information
.
One demonstration of this comes from experiments on ferrets. If you rewire the ferret visual pathway from birth, so that instead of going to the visual cortex it ends up in the auditory cortex, then the auditory cortex, which should be specialized for hearing, ends up doing a pretty good job of processing vision, allowing the ferret to see. This auditory region will even take on characteristics (such as having neurons specialized for representing the angle of an object) that the visual cortex would otherwise process. It isn’t quite as good as if the visual cortex were doing the job, but it is quite functional. Another striking example comes from people blind from birth, who, when reading Braille, process the words mainly in the visual regions of their brain. Given that the visual regions have no sight-based input with which to work, this portion of cortex has adapted to take on the Braille-reading task instead. These sorts of examples show that all sensory processing is just information to the brain, and that almost any brain region can process any type of information, even if it was originally earmarked in development for a specific type of data.
Importantly, especially in more complex nervous systems, our perception of the world is far from being a mere copy of the physical information hitting our senses. Instead, an active, ever-changing, yet unconscious statistical machine is in force, transforming the basic information we receive into a detailed model of the immediate world, including how it is likely to change in the near future, and what in the environment is particularly relevant to us.
But there’s no point just filling up your sensory bank with information, however well processed, if you’re just going to hoard it, never using that hard-earned knowledge for useful purchases. What’s needed is a way to tie information to behavior—in other words, to move. In simple animals, this is all too clear, as the connection between what they perceive and how they act is usually direct and almost immediate: A worm, sensing food, will go toward it, or sensing some threat, will move away. But the more sophisticated an animal, the more processing takes place in the gap between senses and movement.
For humans, the brain’s main evolutionary purpose—moving the body—is rather obscured by just how much happens inside; the link between what we sense and how we behave is a long, fragile tangle of thought. The processing and the calculation of what action is best out of the millions available to our finely tuned bodies and remarkably accurate world picture has taken center stage. Nevertheless, it’s useful to entertain the interesting perspective that, essentially, even a human brain is there primarily to move the body around in the most useful ways.
The first mechanism for movement is instinctive behavior, a tool that all animals possess. An instinct is a genetically determined brain program to marry some sensory input with some prescribed response—designed, as always, to maximize the survival and reproduction of the animal. Here the genes are basically exploiting the ability of the brain to store and act upon information too complex to be executed only in a direct genetic form. For instance, if I unwittingly touch a delicious pie that has just been removed from the oven, before I know what has happened, I find my hand darting away from the potentially burning source. It takes a moment or two for my consciousness to catch up and realize that I nearly burned myself. The primitive regions of my brain sensed the heat and programmed the response before my higher cortical regions were even informed, either of the heat or the arm twitch. It all looks very simple and natural, especially when consciousness appears to be merely a spectator at the event, but you still need some surprisingly complex neuronal processing to make this important reflex occur—you need to know in which direction to send the arm, which muscles to trigger, by how much, and so on.
Matching responses to fixed sensory input is all very well, but on its own, it doesn’t get you all that far. In one episode of
The Simpsons
, Lisa’s original school science fair exhibit is destroyed by her mischievous brother Bart. In revenge, she decides that Bart himself will be an unwitting component of her new exhibit, so she carries out a series of tests to determine whether Bart or a hamster is smarter. In one experiment, the hamster starts nibbling at a piece of food, but receives a mild shock. It immediately learns never to touch the food again. Cut to Bart, who discovers a cupcake with electrodes attached and a sign in front boldly warning, “DO NOT TOUCH.” Chucking the sign behind him nonchalantly, he reaches for the cupcake, and his hand darts away as he receives a sharp electric shock. But this just makes him angry, so he reaches again. Surprise surprise, he’s shocked again and his hand darts back. He continues repeatedly to reach for the food and repeatedly shocks himself. In the real world, I don’t think Bart would have made it to the age of ten. But what he—and the hamster—clearly illustrate is that it’s all very well having instincts, but without even the most basic kind of learning, they don’t get you very far.
Even the simplest form of learning is usually surprisingly powerful. If an animal tries to eat a food source that is toxic, it will quickly not only link this input with the result, but also avoid anything similar in the future. This is an incredible feat. The animal has managed to link in memory a useful, abstract copy of the object with its effect (more intelligent animals will add to this mix the relative intensity of the effect—for instance, chocolate is more tasty than spinach). What is more amazing is how few brain cells you need to learn in relatively sophisticated ways like this. Returning to the humble nematode worm (specifically
C. elegans
): This tiny worm, all of 1 mm long, has exactly 302 neurons. Nevertheless, it can learn to connect an arbitrary, neutral smell with a nearby food source and approach the smell whenever it is presented, presumably in the assumption that food is soon to follow. It can learn to stop moving away if some initially potentially dangerous stimulus repeatedly shows itself to be harmless, thus scrubbing out a previously firm, important belief. The nematode worm even shows crude seeds of socialization, with some strains only stopping to eat when in a group.
When you move up in sophistication to the fruit fly, another commonly studied animal, you can create a surprisingly brainy biological machine with only about 200,000 neurons. As well as learning by simple association, like nematode worms, fruit flies sleep, have short- and long-term memories, and even have a primitive analogue of attention—all inside a brain the size of a poppy seed.
Learning is all very well, but what should I try to learn when surrounded by infinite potential facts? And
why should
I bother to learn to avoid the pie until it cools down?
Why should
the worm bother avoiding some type of toxic food? Why not learn instead that the wind makes that leaf there on the right bob up and down a little faster than the one on the left? The crucial answer is that animals are constrained by a value system—the representation of what’s good or bad, pleasant or painful. Animal behavior is closely governed by this system. And this mechanism, via evolution, has been honed to closely map that which is beneficial or detrimental to survival and reproduction.
This value system labels any remotely relevant stimulus according to whether it will aid or imperil the animal and how great the danger or benefit is. Simple animals will enshrine this in their movements—they will approach what is good (such as food or sex) and escape from what is bad (such as predators). In many animals, the speed and level of permanence of learning is also related to just how beneficial or dangerous the source is. For instance, a dog may almost immediately learn that when its owner starts screaming at it, a kick is sure to follow, but it might take many repeats of its owner calling out “new water” for it to realize that there is something to drink again, since water is in plentiful supply, and its thirst is rarely life-threatening.
Though a simple animal may learn what is good or bad about the environment, this doesn’t explain
in what way
it is good or bad.
C. elegans
will back up if it smells something paired with a toxic food source in the same way that it backs up if it senses a vibration—there in fact is little distinction in its brain between the two events. This is where emotions extend this value system. Emotions put meat on the bones of what is beneficial or harmful. The three main primitive emotions are fear, disgust, and anger. If we’re afraid of some smell, we sprint away—or freeze in cover—while also being far more alert to the danger, ready to notice its slightest detail, and actively prepared to escape again if necessary. If we find that a smell evokes memories of a disgusting meal, it’s just plain silly to sprint away through the forest as fast as we can. Instead, we will merely slowly back off and look for something else to eat. So basic emotions can shape our behavior in far more sophisticated, prepackaged ways, in relation to different categories of threat, than a crude value system that only ever has two labels: good or bad.
Some psychologists have suggested that we recognize our own emotions wholly by what we pick up about our body states. When we’re angry, they suggest, we’re actually just noticing that our heart rates have increased, our fists are clenching, and so on. Again, emotions are largely a signal to move, to change the environment to maximize our survival and reproduction within it.
Of course, humans, in contrast to simple animals, have a large range of different, more complex emotions, such as jealousy, schadenfreude, or a sense of injustice. The variety of our feelings has increased dramatically compared with many other mammals because our evolutionary heritage is that of a large, complex, hierarchical society, which places many more demands on managing social politics and a diverse group of friends. Some emotions may destroy our lives, such as the obsessive love we may feel for an unavailable woman, or the addictive rush of gambling. Nevertheless, all the feelings we experience have a clear evolutionary foundation. Our brains perceive features of the environment to be good or bad for us, even if the computation can go askew at times due to the complexities of our lives. And many complex, seemingly subtle emotions are combinations of simpler ones, each with a clear evolutionary purpose. Jealousy, for instance, is a deep desire for some object, such as a mate, and primitive anger at the threat to our possessing this object.
In fact, the more we study our chimpanzee cousins, the more emotions we find that we seem to share with them, and the more apparent it becomes that our own large set of sophisticated emotions have an evolutionary underpinning. The latest research additions, for instance, include findings on the existence in chimpanzees of a moral sense, and possibly even a degree of wonder. If a chimp encounters a waterfall, it will sometimes display in front of it, touch it, and stare at it for prolonged periods of time—even if no other chimps are around (thus helping to rule out the possibility of an alpha male showing off to assert his authority over his group). If there is a thunderstorm, both males and females have been known to play out a kind of dance. Some primatologists have speculated that this is because our simian cousins can occasionally show intense curiosity, even a kind of reverence, for dramatic displays of nature.

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