Brain Rules (Updated and Expanded). John Medina

to write a seminal paper on fitness and mortality. The study stands as a landmark example of how to do work with rigor and integrity in this field. His analysis inspired other investigators. What about using exercise not only as prevention, they asked, but as intervention, to treat mental disorders such as depression and anxiety? That turned out to be a good line of questioning.

      A growing body of work now suggests that physical activity can powerfully affect the course of both diseases. We think it’s because exercise regulates the release of most of the biochemicals associated with maintaining mental health. In one experiment on depression, rigorous exercise was substituted for antidepressant medication. Even when compared to medicated controls, the treatment outcomes were astonishingly successful. For both depression and anxiety, exercise is beneficial immediately and over the long term. It is equally effective for men and women. The longer the person exercises, the greater the effect. Although exercise is not a substitute for psychiatric treatment (which usually involves therapy along with medication), the role of exercise on mood is so pronounced that many psychiatrists prescribe physical activity as well. It is especially helpful in severe cases and for older people.

      In asking what else exercise can do, researchers looked beyond our oldest members to our youngest.

       6) Does exercise help kids do better in school?

      The number of studies in children is downright microscopic. Still, the data point in a familiar direction. Physically fit children identify visual stimuli much faster than sedentary ones. They appear to concentrate better. Brain-activation studies show that children and adolescents who are fit allocate more cognitive resources to a task and do so for longer periods of time. “Kids pay better attention to their subjects when they’ve been active,” Dr. Antronette Yancey said in an interview with NPR. “Kids are less likely to be disruptive in terms of their classroom behavior when they’re active. Kids feel better about themselves, have higher self-esteem, less depression, less anxiety. All of those things can impair academic performance and attentiveness.”

      Of course, many ingredients make up academic performance. Finding out what those components are—and then which are most important for improving performance—is difficult. But these preliminary findings hint that exercise may be one key ingredient.

      An exercise in road building

      Why exercise works so well in the brain, at a molecular level, can be illustrated by competitive food eaters—or, less charitably, professional pigs. The crest of the International Federation of Competitive Eating proudly displays the motto In Voro Veritas—literally, “In Gorging, Truth.” Like any sporting organization, competitive food eaters have their heroes. The reigning gluttony god is Takeru “Tsunami” Kobayashi. He is the recipient of many eating awards, including the vegetarian dumpling competition (83 dumplings downed in eight minutes), the roasted pork bun competition (100 in 12 minutes), and the hamburger competition (97 in eight minutes). Kobayashi also is a world champion hot-dog eater. One of his few losses was to a 1,089-pound Kodiak bear. In a 2003 Fox-televised special called Man vs. Beast, the mighty Kobayashi consumed only 31 bunless dogs compared with the ursine’s 50, all in about 2½ minutes. The Tsunami would not accept defeat. In 2012, Kobayashi ate 60 bunless dogs in that amount of time. But my point isn’t about speed.

      Like the Tsunami’s, the brain’s appetite for energy is enormous. 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.

      That energy supply is glucose, a type of sugar that is one of the body’s favorite resources. After all of those hot dogs slide down the Tsunami’s throat, his stomach’s acid and his wormy intestines tear the food apart (not getting much help from the teeth, in his case) and reconfigure it into glucose. Glucose and other metabolic products are absorbed into the bloodstream via the small intestines. The nutrients travel to all parts of the body, where they are deposited into cells, which make up the body’s various tissues. The cells seize the sweet stuff like sharks in a feeding frenzy. Cellular chemicals greedily tear apart the molecular structure of glucose to extract its sugary energy.

      This energy extraction is so violent that atoms are literally ripped asunder in the process. As in any manufacturing process, such fierce activity generates a fair amount of toxic waste. In the case of food, this waste consists of a nasty pile of excess electrons shredded from the atoms in the glucose molecules. Left alone, these electrons slam into other molecules within the cell, transforming them into some of the most toxic substances known to humankind. They are called free radicals. If not quickly corralled, they will wreck havoc on the innards of a cell and, cumulatively, on the rest of the body. These electrons are fully capable, for example, of causing mutations in your DNA.

      The reason you don’t die of electron overdose is that the atmosphere is full of breathable oxygen. The main function of oxygen is to act like an efficient electron-absorbing sponge. At the same time the blood is delivering glucose to your tissues, it is also carrying these oxygen sponges. Any excess electrons are absorbed by the oxygen and, after a bit of molecular alchemy, are transformed into equally hazardous—but now fully transportable—carbon dioxide. The blood is carried back to your lungs, where the carbon dioxide leaves the blood and you exhale it. So whether you are a competitive eater or a typical one, the oxygen-rich air you inhale keeps the food you eat from killing you. 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.

      Getting energy into tissues and getting toxic electrons out are essentially matters of access. That’s why blood—acting as both waitstaff and hazmat team—has to be everywhere inside you. Any tissue without enough blood supply is going to starve to death, your brain included. More access to blood is better. And even in a healthy brain, the blood’s delivery system can be improved.

      That’s where exercise comes in.

      It reminds me of a seemingly mundane little insight that literally changed the history of the world. John Loudon McAdam, a Scottish engineer living in England in the early 1800s, noticed the difficulty people had trying to move goods and supplies over hole-filled, often muddy, frequently impassable dirt roads. He had the splendid idea of raising the level of the road using layers of rock and gravel. This immediately made the roads less muddy and more stable. As county after county adopted his process, now called macadamization, people instantly got more dependable access to one another’s goods and services. Offshoots from the main roads sprang up. Pretty soon entire countrysides had access to far-flung points using stable arteries of transportation. Trade grew. People got richer. By changing the way things moved, McAdam changed the way we lived.

      What does this have to do with exercise? McAdam’s central notion wasn’t to improve goods and services, but to improve access to goods and services. You can do the same for your brain by increasing the roads in your body, namely your blood vessels, through exercise. Exercise does not provide the oxygen and the food. It provides your body greater access to the oxygen and the food.

      How this works is easy to understand. When you exercise, you increase blood flow across the tissues of your body. Blood flow improves because exercise stimulates the blood vessels to create a powerful, flow-regulating molecule called nitric oxide. As the flow improves, the body makes new blood vessels, which penetrate deeper and deeper into the tissues of the body. This allows more access to the bloodstream’s goods and services, which include food distribution and waste disposal. The more you exercise, the more tissues you can feed and the more toxic waste you can remove. This happens all over the body. That’s why exercise improves the performance of most human functions. You stabilize existing transportation structures and add new ones, just like McAdam’s roads. All of a sudden, you are becoming