Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School

by John Medina

The brain appears to be designed to (1) solve problems (2) related to surviving (3) in an unstable outdoor environment, and (4) to do so in nearly constant motion. I call this the brain’s performance envelope.

Though we have been stuffing them into classrooms and cubicles for decades, our brains actually were built to survive in jungles and grasslands. We have not outgrown this.

There are two ways to beat the cruelty of a harsh environment: You can become stronger or you can become smarter. We did the latter.

One trait really does separate us from the gorillas: the ability to use symbolic reasoning.

Stated informally, we can make things up that aren’t there. We are human because we can fantasize. We are so good at dual representation, we combine symbols to derive layers of meaning. It gives us the capacity for language, and for writing down that language. It gives us the capacity to reason mathematically. It gives us the capacity for art. Combinations of circles and squares become geometry and Cubist paintings. Combinations of dots and squiggles become music and poetry. There is an unbroken intellectual line between symbolic reasoning and the ability to create culture. And no other creature is capable of doing it.

Eventually, we migrated out of Africa in successive waves, our direct Homo sapiens ancestors making the journey as little as 100,000 years ago. Then, 40,000 years ago, something almost unbelievable happened. Our ancestors suddenly took up painting and sculpture, creating fine art and jewelry. This change was both abrupt and profound. Thirty-seven thousand years later, we were making pyramids. Five thousand years after that, rocket fuel. Many scientists think our growth spurt can be explained by the onset of dual-representation ability. And many think our dual-representation ability—along with physical changes that precipitated it—can be explained by a nasty change in the weather.

The founding population of our direct ancestors is not thought to have been much larger than 2,000 individuals; some think the group was as small as a few hundred.

Because the trees were gone or going, we needed to travel increasingly long distances between food sources. Walking on two legs instead of four both freed up our hands and used fewer calories. It was energy-efficient. Our ancestral bodies used the energy surplus not to pump up our muscles but to pump up our minds.

Your most ancient neural structure is the brain stem, or “lizard brain.” This rather insulting label reflects the fact that the brain stem functions the same way in you as in a Gila monster. The brain stem controls most of your body’s housekeeping chores: breathing, heart rate, sleeping, waking.

Sitting atop your brain stem is your “mammalian brain.” It appears in you the same way it does in many mammals, such as house cats, which is how it got its name. It has more to do with your animal survival than with your human potential. Most of its functions involve what some researchers call the “four Fs”: fighting, feeding, fleeing, and … reproductive behavior.

The amygdala allows you to feel rage. Or fear. Or pleasure. Or memories of past experiences of rage, fear, or pleasure. The amygdala is responsible for both the creation of emotions and the memories they generate.

The hippocampus converts your short-term memories into longer-term forms.

The thalamus is one of the most active, well-connected parts of the brain—a control tower for the senses. Sitting squarely in the center of your brain, it processes and routes signals sent from nearly every corner of your sensory universe.

Folded atop all of this is your “human brain,” a layer called the cortex.

Each region of the cortex is highly specialized, with sections for speech, for vision, for memory.

A lot of mothers and babies died on the way to reaching an anatomical compromise. Human pregnancies are still remarkably risky without modern medical intervention. The solution? Give birth while the baby’s head is small enough to fit through the birth canal. The problem? You create childhood. Most mammals reach adulthood within months. Our long childhood gave the brain time to finish its developmental programs outside the womb. It also created a creature vulnerable to predators for years and not reproductively fit for more than a decade. That’s an eternity when you live in the great outdoors, as we did for eons.

Of course, it was no use having babies who took years to grow if the adults were eaten before they could finish their thoughtful parenting. We weaklings needed to out-compete the big boys on their home turf, leaving our new home safer for sex and babies. We decided on a strange strategy. We decided to try to get along with each other.

Brain Rule #1 The human brain evolved, too. • The brain appears to be designed to (1) solve problems (2) related to surviving (3) in an unstable outdoor environment, and (4) to do so in nearly constant motion. • We started with a “lizard brain” to keep us breathing, then added a brain like a cat’s, and then topped those with the thin layer known as the cortex—the third, and powerful, “human” brain. • We adapted to change itself, after we were forced from the trees to the savannah when climate swings disrupted our food supply. • Going from four legs to two to walk on the savannah freed up energy to develop a complex brain. • Symbolic reasoning is a uniquely human talent. It may have arisen from our need to understand one another’s intentions and motivations. This allowed us to coordinate within a group, which is how we took over the Earth.

Homo sapiens started in Africa and then took a victory lap around the rest of the world.

Given our relative wimpiness in the animal kingdom (we don’t even have enough body hair to survive a mildly chilly night), what these data tell us is that we grew up in top physical shape, or we didn’t grow up at all. These data also tell us the human brain became the most powerful in the world under conditions where motion was a constant presence.

One of the greatest predictors of successful aging, they found, is the presence or absence of a sedentary lifestyle.

Just about every mental test possible was tried. No matter how it was measured, the answer was consistently yes: A lifetime of exercise results in a sometimes astonishing elevation in cognitive performance, compared with those who are sedentary.

researchers looked at more than 10,000 British civil servants between the ages of 35 and 55, grading their activity levels as low, medium, or high. Those with low levels of physical activity were more likely to have poor cognitive performance. Fluid intelligence, the type that requires improvisatory problem-solving skills, was particularly hurt by a sedentary lifestyle.

Like producers of a makeover show, researchers found a group of elderly couch potatoes, measured their brain power, exercised them, and then reexamined their brain power. The researchers consistently found that all kinds of mental abilities began to come back online—after as little as four months of aerobic exercise. A different study looked at school-age children. Children jogged for 30 minutes two or three times a week. After 12 weeks, their cognitive performance had improved significantly compared with prejogging levels. When the exercise program was withdrawn, the scores plummeted back to their preexperiment levels. Scientists had found a direct link.

In the laboratory, the gold standard appears to be aerobic exercise, 30 minutes at a clip, two or three times a week. Add a strengthening regimen and you get even more cognitive benefit.

Your lifetime risk for general dementia is literally cut in half if you participate in physical activity. Aerobic exercise seems to be the key. With Alzheimer’s, the effect is even greater: Such exercise reduces your odds of getting the disease by more than 60 percent.

The researchers showed you have to participate in some form of exercise just twice a week to get the benefit. Bump it up to a 20-minute walk each day, and you can cut your risk of having a stroke—one of the leading causes of mental disability in the elderly—by 57 percent.

The brain gobbles up 20 percent of the body’s energy, even though it’s only about 2 percent of the body’s weight. When the brain is fully working, it uses more energy per unit of tissue weight than a fully exercising quadricep. In fact, the human brain cannot simultaneously activate more than 2 percent of its neurons at any one time. More than this, and the brain’s energy supply becomes so quickly exhausted that you will faint.

How important is oxygen? The three requirements for human life are food, drink, and fresh air. But their effects on survival have very different timelines. You can live for 30 days or so without food, and you can go for a week or so without drinking water. Your brain, however, is so active that it cannot go without oxygen for more than five minutes without risking serious and permanent damage. When the blood can’t deliver enough oxygen sponges, toxic electrons overaccumulate.

Recall that our evolutionary ancestors were used to walking up to 12 miles per day. This means that our brains were supported for most of our evolutionary history by Olympic-caliber bodies.

The benefits of exercise seem nearly endless because its impact is systemwide, affecting most physiological systems. Exercise makes your muscles and bones stronger, improving your strength and balance. It helps regulate your appetite, reduces your risk for more than a dozen types of cancer, improves the immune system, changes your blood lipid profile, and buffers against the toxic effects of stress (see the Stress chapter). By enriching your cardiovascular system, exercise decreases your risk for heart disease, stroke, and diabetes. When combined with the intellectual benefits exercise appears to offer, we have in our hands as close to a magic bullet for improving human health as exists in modern medicine. So I am convinced that integrating exercise into those eight hours at work or school will only make us normal. All we have to do is move.

Brain Rule #2 Exercise boosts brain power. • Our brains were built for walking—12 miles a day! • To improve your thinking skills, move. • Exercise gets blood to your brain, bringing it glucose for energy and oxygen to soak up the toxic electrons that are left over. It also stimulates the protein that keeps neurons connecting. • Aerobic exercise just twice a week halves your risk of general dementia. It cuts your risk of alzheimer’s by 60 percent.

Some researchers, though not all, think this equanimity in tension drives the need to nap. Some think that a long sleep at night and a short midday nap represent default human sleep behavior, that it is part of our evolutionary history.

Mendeleyev single-handedly systematized the entire science of chemistry. His Periodic Table of the Elements—a way of organizing every atom that had so far been discovered—was so prescient, it allowed room for all of the elements yet to be found and even predicted some of their properties. But what’s most extraordinary is this: Mendeleyev says he came up with the idea in his sleep. Contemplating the nature of the universe while playing solitaire one evening, he nodded off. When he awoke, he knew how all of the atoms in the universe were organized, and he promptly created his famous table. Interestingly, he organized the atoms in repeating groups of seven, just the way you play solitaire.

Students were given a series of math problems and prepped with a method to solve them. The students weren’t told there was also an easier “shortcut” way to solve the problems, potentially discoverable while doing the exercise. The question was: Is there any way to jump-start, even speed up, the insight into the shortcut? The answer was yes, if you allow them to sleep on it. If you let 12 hours pass after the initial training and ask the students to do more problems, about 20 percent will have discovered the shortcut. But, if in that 12 hours you also allow eight or so hours of regular sleep, that figure triples to about 60 percent. No matter how many times the experiment is run, the sleep group consistently outperforms the non-sleep group about three to one.

Sleep also has been shown to enhance tasks that involve visual texture discrimination (the ability to pick out an object from an ocean of similar-looking objects), motor adaptations (improving movement skills), and motor sequence learning. The type of learning that appears to be most sensitive to sleep improvement is that which involves learning a procedure. Simply disrupt the night’s sleep at specific stages and retest in the morning, and you eliminate any overnight learning improvement. Clearly, for specific types of intellectual skill, sleep can be a great friend to learning.

Brain Rule #3 Sleep well, think well. • The brain is in a constant state of tension between cells and chemicals that try to put you to sleep and cells and chemicals that try to keep you awake. • The neurons of your brain show vigorous rhythmical activity when you’re asleep—perhaps replaying what you learned that day. • People vary in how much sleep they need and when they prefer to get it, but the biological drive for an afternoon nap is universal. • Loss of sleep hurts attention, executive function, working memory, mood, quantitative skills, logical reasoning, and even motor dexterity.

There is no unique grouping of physiological responses capable of telling a scientist whether you are experiencing stress. That’s because many of the mechanisms that cause you to shrink in horror from a predator are the same mechanisms used when you are having sex—or even while you are consuming your Thanksgiving dinner. To your body, saber-toothed tigers and orgasms and turkey gravy look remarkably similar. An aroused physiological state is characteristic of both stress and pleasure.

About one million people stay home from work every day because of stress (about 40% of all absences occur because of tension felt at work!). The Bureau of Labor Statistics found the average amount of time off due to stress was 20 days. That’s costly.

The perfect storm of occupational stress appears to be a combination of two factors: (1) a great deal is expected of you, and (2) you have no control over whether you will perform well.

About 36 percent of the employees in an insurance company who enrolled in mindfulness training noticed a marked reduction in stress after taking the program. About 30 percent noticed an improvement in sleep. It has also been found to be effective against depression.

They found that babies raised in the intervention households didn’t look anything like the babies raised in the controls. Their nervous systems didn’t develop the same way. Their behaviors weren’t in the same emotional universe. Children in the intervention groups didn’t cry as much. They had stronger attention-shifting behaviors. They responded to external stressors in remarkably stable ways. Physiologically, the intervention babies showed all the cardinal signs of healthy emotional regulation, while the controls showed all the signs of unhealthy, disorganized nervous systems. The differences were remarkable and revealed something hopeful and filled with common sense.

Brain Rule #4 Stressed brains don’t learn the same way. • Your body’s defense system—the release of adrenaline and cortisol—is built for an immediate response to a serious but passing danger, such as a saber-toothed tiger. Chronic stress, such as hostility at home, dangerously deregulates a system built only to deal with short-term responses. • Under chronic stress, adrenaline creates scars in your blood vessels that can cause a heart attack or stroke, and cortisol damages the cells of the hippocampus, crippling your ability to learn and remember. • Individually, the worst kind of stress is the feeling that you have no control over the problem—you are helpless. • Emotional stress has huge impacts across society, on children’s ability to learn in school and on employees’ productivity at work.

Charles Darwin noted similar differences between the brains of wild animals and their domestic counterparts. The brains of wild animals were 15 to 30 percent larger than those of their tame, domestic counterparts. It appeared that the cold, hard world forced the wild animals into a constant learning mode. Those experiences wired their brains much differently.

The brain acts like a muscle: The more activity you do, the larger and more complex it can become. Whether that equates to more intelligence is another issue, but one fact is indisputable: What you do in life physically changes what your brain looks like. You can wire and rewire your brain with the simple choice of which musical instrument—or professional sport—you play.

What does a nerve cell look like? Like an uprooted tree: a large mass of roots on one end, connected to a small mass of branches on the other. The root mass in a nerve cell is called the cell body, and within it lies the nucleus. The tips of the roots are called dendrites. The thin, connecting trunk is called an axon, and the smaller mass of branches is called the axon terminal.

Suddenly, a researcher whips out a photo of Jennifer Aniston and shows it to the patient. A neuron in the man’s head fires. The researcher lets out a war whoop. This experiment really happened. The neuron in question responded to seven photographs of actress Jennifer Aniston, while it practically ignored the 80 other images of everything else, including famous and nonfamous people. Lead scientist Quian Quiroga said, “The first time we saw a neuron firing to seven different pictures of Jennifer Aniston—and nothing else—we literally jumped out of our chairs.” There is a neuron lurking in your head that is stimulated only when Jennifer Aniston is in the room.

Psychologist Howard Gardner believes we have at least seven categories of intelligence: verbal/linguistic, musical/rhythmic, logical/mathematical, spatial, bodily/kinesthetic, interpersonal, and intrapersonal. It’s a much broader idea of intelligence than the standard IQ test implies.

Brain Rule #5 Every brain is wired differently. • What you do and learn in life physically changes what your brain looks like—it literally rewires it. • The various regions of the brain develop at different rates in different people. • Neurons go through a growth spurt and pruning project during the terrible twos and teen years. • No two people’s brains store the same information in the same way in the same place. • We have a great number of ways of being intelligent, many of which don’t show up on IQ tests.

Different cultures create different expectations as well. For example, Science magazine notes that “Asians pay more attention to context and to the relationships between focal (foreground) objects and background in their descriptions of visual scenes, whereas Americans mention the focal items with greater frequency.” Such differences can affect how an audience perceives a given business presentation or class lecture.