Welcome to Your Brain (2 page)

yourself. Your brain lets you watch a sunset, learn a language, tell a joke, recognize a friend, run from

danger, and read this sentence.

In the last twenty years, neuroscientists have learned a lot about how your brain does all these

things. It’s a complicated subject, but we think it doesn’t have to be intimidating. This book will give

you the inside scoop on how your brain really works—and how you can help it work better.

Your brain has many ways of doing its job, including tricks and shortcuts that help it work

efficiently—but may lead you to make predictable mistakes. By reading this book, you’ll find out how

you accomplish the things you do every day. Along the way we’ll explode some of the myths that you

might believe because “everybody knows” they’re true. For instance, you don’t really use only 10

percent of your brain. (Come on.)

Knowing your brain better can be both fun and useful. We will show you simple changes that will

allow you to do more with your brain and help you lead a happier and more productive life. We’ll

also show you how disease can damage your brain—and suggest ways to prevent or repair this

damage.

This book is like a guided tour: we’ll see all the best sights and most important spots. But you

don’t have to start at the beginning. You can dip in anywhere and read this book in small pieces

because each chapter stands on its own. In each one, you’ll find fun facts, cocktail party-ready stories

to amuse your friends, and practical tips to help you use your brain better.

• In
part 1
, we introduce the star of the show, your brain. We pull aside the curtain to show what is

happening behind the scenes and explain how your brain helps you survive in the world.

• In
part 2
, we take a tour of your senses, explaining how you see, hear, touch, smell, and taste.

• In
part 3
, we show how your brain changes through life, from birth to old age.

• In
part 4
, we examine your brain’s emotional systems, focusing on how they help you navigate life

effectively.

• In
part 5
, we discuss your reasoning abilities, including decision making, intelligence, and gender

differences in cognition.

• In
part 6,
we examine altered states of your brain—consciousness, sleep, drugs and alcohol, and

disease.

Leave this book by your bedside or on your coffee table, and dip in anywhere, anytime. We hope

you’ll be enlightened and entertained, and that after reading a few pages you will want to read the

whole book. Now pull up a chair and get ready to find out about your brain—and about yourself!

Part One

Your Brain and the World

Can You Trust Your Brain?

Gray Matter and the Silver Screen: Popular Metaphors of How the Brain Works

Thinking Meat: Neurons and Synapses

Fascinating Rhythms: Biological Clocks and Jet Lag

Bring Your Swimsuit: Weight Regulation

Chapter 1

Can You Trust Your Brain?

Your brain lies to you a lot. We’re sorry to have to break the news to you, but it’s true. Even

when your brain is doing essential and difficult stuff, you’re not aware of most of what’s going on.

Your brain doesn’t intend to lie to you, of course. For the most part, it’s doing a great job,

working hard to help you survive and accomplish your goals in a complicated world. Because you

often have to react quickly to emergencies and opportunities alike, your brain usually aims to get a

half-assed answer in a hurry rather than a perfect answer that takes a while to figure out. Combined

with the world’s complexity, this means that your brain has to take shortcuts and make a lot of

assumptions. Your brain’s lies are in your best interest—most of the time—but they also lead to

predictable mistakes.

One of our goals is to help you understand the types of shortcuts and hidden assumptions that your

brain uses to get you through life. We hope this knowledge will make it easier for you to predict when

your brain is a source of reliable information and when it’s likely to mislead you.

The problems start right up front, when the brain takes in information from the world through the

senses. Even if you are sitting quietly in a room, your brain receives far more information than it can

hold on to, or than you need to decide how to act. You may be aware of the detailed pattern of colors

in the rug, the photographs on the wall, and the sounds of birds outside. Your brain perceives many

other aspects of the scene initially but quickly forgets them. Usually these things really aren’t

important, so we don’t often notice how much information we lose. The brain commits many lies of

omission, as it discards most of the information in the world as soon as it is deemed to be

unremarkable.

Lawyers know this principle. Eyewitnesses are notoriously unreliable, in part because they

imagine—as most of us do—that they see and remember more details than they really can. Lawyers

can use this knowledge to discredit witnesses by tempting them to say they saw something that the

lawyer can disprove, casting doubt on the rest of the witness’s testimony.

Did you know? Looking at a photograph is harder than playing chess

You may think that you know what your brain does, but you actually notice only a small

fraction of its activity—and what your brain accomplishes behind your back is some of its

hardest work. When computer scientists first began trying to write programs to mimic

human abilities, they found that it was relatively easy to get computers to follow logic rules

and do complex mathematics, but very hard to get them to figure out what they were seeing

in a visual image or to move smoothly through the world. Today’s best computer chess

programs can beat a grand master, at least some of the time, but any normal toddler can kick

the butt of the top programs when it comes to making sense of the visual world.

One difficult step, as it turns out, is identifying individual objects in a visual scene.

When we look at, say, a dinner table, it seems obvious that the water glass is one object

that is in front of another object, like a vase of flowers, but this turns out to be a

sophisticated calculation with many possible answers. You only notice this ambiguity

occasionally, when you see something briefly enough to misidentify it, like when that rock

in the middle of the dark road suddenly turns into the neighbor’s cat. The brain sorts out

these possibilities based on its previous experience with objects, including having seen the

two objects separately and in other combinations. Have you ever taken a picture in which a

tree seemed to be growing out of someone’s head? When you snapped the photo, you didn’t

notice the problem because your brain had efficiently separated the objects based on their

different distances from your eyes. Later on, the two-dimensional photo didn’t contain the

same information about distances, so it looked like the two objects were on top of each

other.

In addition to throwing away information, the brain also has to decide whether to take shortcuts,

depending on how it values speed against accuracy in a particular situation. Most of the time, your

brain favors speed, interpreting events based on rules of thumb that are easy to apply but not always

logical. The rest of the time, it uses the slow, careful approach that’s appropriate for doing math or

solving logic puzzles. Psychologist Daniel Kahneman won the Nobel Prize in Economics for studying

these rules of thumb and how they influence real-life behavior. (His longtime collaborator, Amos

Tversky, passed away before he could share the honor.)

Did you know? Are we in our right minds?

When people talk about the “right brain” and the “left brain,” they’re referring to the

two sides of the cortex. While there are some real differences in function between them, the

distinctions are often misunderstood.

Most people’s speech is controlled by the left side of the brain, which is also

responsible for mathematics and other forms of logical problem solving. Curiously, it is

also the source of many misremembered or confabulated details, and it is the home of the

“interpreter” discussed on the next page. All in all, the left side of the brain seems to have

an intense need for logic and order—so intense that if something doesn’t make sense, it

usually responds by inventing some plausible explanation.

The right side is much more literal and truthful when it reports what happened. It

controls spatial perception and the analysis of objects by touch, and excels at visual-motor

tasks. Rather than being “artistic” or “emotional,” the right brain is simply more grounded.

It’s a Joe Friday type, and if it could talk, it would probably say, “Just the facts,

ma’am.”

The take-home message from their research is that logical thinking requires a lot of effort. For

example, try to solve the following problem quickly: A bat and a ball together cost $1.10. The bat

costs $1 more than the ball. How much does the ball cost? Most people say 10¢, which is intuitive

but wrong. (The bat costs $1.05, and the ball costs 5¢.) Mental shortcuts like this are very common:

in fact, people are likely to use them in almost all situations unless they’re strongly cued that they

should be using logic instead. Most of the time, the intuitive answer is good enough to get by, even

when it is wrong.

In everyday life, we’re not typically asked to solve logic problems, but we are often asked to

make judgments about people we don’t know very well. Kahneman and Tversky used another

approach to show that these judgments aren’t logical either. For example, they would start an

experiment by telling people about Linda: “Linda is thirty-one years old, single, outspoken, and very

bright. She majored in philosophy. As a student, she was deeply concerned with issues of

discrimination and social justice and also participated in antinuclear demonstrations.” Then they

asked people to pick the phrase that seemed most likely to describe Linda from a carefully contrived

list of traits.

Most people thought it was more probable that (a) “Linda is a bank teller who is active in the

feminist movement” than (b) “Linda is a bank teller.” Choice (a) makes intuitive sense because many

of Linda’s other characteristics—concern about social justice and so on—suggest that she might be

active in the feminist movement. Yet that is not the right answer, because everyone who is (a) “a bank

teller who is active in the feminist movement” is also (b) “a bank teller.” And of course the group in

(b) includes other bank tellers who are reactionary or apathetic.

In such a case, even sophisticated participants like graduate students in statistics make the error of

reaching a conclusion that directly contradicts logic. This strong tendency to attribute groups of

related characteristics to people without much evidence is a quick way of estimating likely outcomes,

but it may also be a root cause of many of the stereotypes and prejudices that are common in society.

To make matters worse, many of the stories we tell ourselves don’t even reflect what’s actually

happening in our own heads. A famous study of brain-damaged patients demonstrates this idea. The

patients had been treated for severe epilepsy by a surgical operation that disconnected the right and

left halves of their brain’s cortex, to prevent seizures from spreading from one side to the other. This

meant that the left half literally didn’t know what the right half was doing, and vice versa.

In one experiment, the scientists showed a picture of a chicken claw to the left side of a patient’s

brain, where the language areas are located, and a picture of a snow scene to the right side of the

brain, which cannot produce speech. Asked to pick a related image from another set of pictures, he

correctly chose a shovel with his left hand (controlled by the right side of the brain) and a chicken

with his right hand (controlled by the left side of the brain). When asked to explain his choices, he

responded: “Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to

clean out the chicken shed.” The scientists concluded that the left side of the brain contains an

“interpreter” whose job is to make sense of the world, even when it doesn’t understand what’s really

happening.

These problems of throwing away information, taking mental shortcuts, and inventing plausible

stories come together in what psychologists call “change blindness.” For an example, look at the two

photographs. What is the difference between them? (Hint: men of a certain age beware!)