Introduction — Making the Connection
The real reason you feel so good when you get your blood pumping has nothing to do with your waistline. It is that exercise makes the brain function at its best, and that benefit is far more important—and far more fascinating—than anything it does for the body.
Exercise is crucial to the way we think and feel. It cues the building blocks of learning in the brain, affects mood, anxiety, and attention, guards against stress, and reverses some of the effects of aging in the brain. In women it can help stave off the sometimes tumultuous effects of hormonal changes. Most people have no idea that toxic levels of stress erode the connections between the billions of nerve cells in the brain, or that chronic depression shrinks certain of its areas. Conversely, exercise unleashes a cascade of neurochemicals and growth factors that can reverse this process, physically bolstering the brain’s infrastructure.
Why should you care how your brain works? Because it is running the show. Right now the front of your brain is firing signals about what you are reading, and how much of it you soak up has a great deal to do with whether there is a proper balance of neurochemicals and growth factors to bind neurons together. If you had half an hour of exercise this morning, you are in the right frame of mind to sit still and focus on this paragraph, and your brain is far more equipped to remember it. In order to cope with anxiousness, for instance, you need to let certain well-worn neural paths grow over while you blaze alternate trails.
In October of 2000, researchers from Duke University made the New York Times with a study showing that exercise is better than sertraline—Zoloft—at treating depression. The news was buried on page fourteen of the Health and Fitness section. If exercise came in pill form, it would be plastered across the front page, hailed as the blockbuster drug of the century. Exercise has a profound impact on cognitive abilities and mental health. It is simply one of the best treatments we have for most psychiatric problems. The hope here is that once you understand how physical activity improves brain function, you will be motivated to include it in your life in a positive way, rather than thinking of it as something you merely should do.
Chapter 1 — Welcome to the Revolution
Students in the Zero Hour PE program at Naperville Central High School work out intensely before their first academic class of the day. At the end of the semester, they show a seventeen percent improvement in reading and comprehension, compared to a ten-point-seven percent improvement among the other literacy students who opted to sleep in and take standard phys ed. The administration is so impressed that it incorporates the program into the high school curriculum as a first-period class called Learning Readiness PE. The experiment continues: literacy students are split between a second-period class—when they are still feeling the effects of the exercise—and an eighth-period class. As expected, the second-period group performs best.
Phil Zientarski, the teacher behind Zero Hour, has a clear view of what his job actually is. “I tell people it’s not my job as a PE teacher to make kids fit,” he says. “My job is to make them know all of the things they need to know to keep themselves fit. Exercise in itself is not fun. It’s work. So if you can make them understand it, show them the benefits—that’s a radical transformation.” And one of the things too many people forget, he adds, is that you have to find something that allows a student to feel comfortable at excelling.
Chapter 2 — Learning
In addition to priming your state of mind, exercise influences learning directly, at the cellular level, improving the brain’s potential to log in and process new information. Darwin taught us that learning is the survival mechanism we use to adapt to constantly changing environments. Inside the microenvironment of the brain, that means forging new connections between cells to relay information. When you learn something—a French word or a salsa step—cells morph in order to encode that information; the memory physically becomes part of the brain. What we now know is that the brain is flexible, or plastic in the parlance of neuroscientists—more Play-Doh than porcelain. Your thoughts, your behavior, and your environment reflect back on your neurons, influencing the pattern of connections. Far from being hardwired, as scientists once envisioned it, the brain is constantly being rewired.
Understanding the mechanics of that rewiring starts with the synapse. An electrical signal shoots down the axon—the outgoing branch of a neuron—until it reaches the synapse, where a neurotransmitter carries the message across the gap in chemical form. On the receiving side, the neurotransmitter plugs into a receptor like a key into a lock, opening ion channels in the cell membrane and turning the signal back into electricity. About eighty percent of the signaling in the brain is carried out by two neurotransmitters that balance each other: glutamate stirs up activity to begin the signaling cascade, and gamma-aminobutyric acid, or GABA, clamps down on activity. The more often a connection is activated, the stronger the attraction becomes—neurons that fire together wire together. This makes glutamate a crucial ingredient in learning. Going for a run is like taking a little bit of Prozac and a little bit of Ritalin, because exercise elevates these same neurotransmitters. But the deeper explanation is that exercise balances neurotransmitters—along with the rest of the neurochemicals in the brain.
Beyond neurotransmitters, there is another class of master molecules that over the past fifteen years has dramatically changed our understanding of how brain connections develop and grow: a family of proteins loosely termed factors, the most prominent of which is brain-derived neurotrophic factor, or BDNF. Whereas neurotransmitters carry out the actual signaling, neurotrophins such as BDNF build and maintain the cell circuitry—the infrastructure itself. About a dozen papers on BDNF were published before 1990, the year scientists discovered that it exists in the brain and nourishes neurons like fertilizer. When researchers sprinkled BDNF onto neurons in a petri dish, the cells automatically sprouted new branches, producing the same structural growth required for learning. That is why BDNF is best thought of as Miracle-Gro for the brain. It is a crucial biological link between thought, emotions, and movement.
To see how this plays out, consider learning a French word. The first time you hear it, nerve cells recruited for a new circuit fire a glutamate signal between each other. If you never practice the word again, the attraction between those synapses naturally diminishes and you forget. But the discovery that astonished memory researchers—and earned Columbia University neuroscientist Eric Kandel a share of the 2000 Nobel Prize—is that repeated activation causes the synapses themselves to swell and make stronger connections. A neuron is like a tree that, instead of leaves, has synapses along its dendritic branches; eventually new branches sprout, providing more synapses to further solidify the connections. These changes are a form of cellular adaptation called synaptic plasticity, and this is where BDNF takes center stage.
Brain scans show that when you learn a new word, the prefrontal cortex lights up with activity. Once the circuit has been established and the word is learned, the prefrontal cortex goes dark. It has overseen the initial stages of the project and can now leave the responsibility to a capable team of employees while it moves on to new challenges. This is how activities like riding a bike become second nature.
The news that exercise itself sparks BDNF came out of left field. Carl Cotman, the neuroscientist who made the discovery, had just finished working on a long-term aging study designed to see what people whose minds hold up best share in common. Among those with the least cognitive decline over a four-year period, three factors turned up: education, self-efficacy, and exercise. By showing that exercise directly spikes the master molecule of the learning process, Cotman nailed down a direct biological connection between movement and cognitive function. One of the prominent features of exercise, he says—sometimes not appreciated in the studies—is an improvement in the rate of learning: “If you’re in good shape, you may be able to learn and function more efficiently.” A 2007 study by German researchers confirmed the practical stakes: people learn vocabulary words twenty percent faster following exercise than before it, and the rate of learning correlated directly with levels of BDNF. People with a gene variation that robs them of BDNF are more likely to have learning deficiencies. As Cotman points out, though, “You can’t just inject BDNF and be smarter. With learning, you have to respond to something in a different way. But the something has to be there.”
Environmental enrichment compounds the effect. The branching caused by learning, exercise, and social contact causes synapses to form more connections, and those connections have thicker myelin sheaths, which allow them to fire signals more efficiently. Neuroscientist Fred Gage found that simply putting a running wheel in a rodent’s cage had a profound effect on the number of new cells born in the brain. Ironically, the same percentage of cells die as in the control group—it is just that you have a bigger starting pool. But in order for a new cell to survive and integrate, it has to fire its axon. Exercise spawns neurons, and the stimulation of environmental enrichment helps those cells survive. The body was designed to be pushed, and in pushing our bodies we push our brains too. Learning and memory evolved in concert with the motor functions that allowed our ancestors to track down food.
Exercise improves learning on three levels: it optimizes your mind-set to improve alertness, attention, and motivation; it prepares and encourages nerve cells to bind to one another, which is the cellular basis for logging in new information; and it spurs the development of new nerve cells from stem cells in the hippocampus. One thing scientists know for sure is that you cannot learn difficult material while exercising at high intensity, because blood is shunted away from the prefrontal cortex, hampering executive function. College students perform poorly on tests of complex learning while working out at seventy to eighty percent of their maximum heart rate. But blood flow shifts back almost immediately after you finish, and the post-exercise window is the perfect time to focus on anything requiring sharp thinking and complex analysis. If you have an important afternoon brainstorming session scheduled, going for a short, intense run at lunchtime is a smart idea.
For sustained improvement in executive function, one scientifically sound study from Japan found that jogging thirty minutes just two or three times a week for twelve weeks was enough. But it is important to mix in some form of activity that demands coordination beyond putting one foot in front of the other. In a comparison study, rats trained on complex motor skills—walking across balance beams, unstable objects, and elastic rope ladders—showed a thirty-five percent increase of BDNF in the cerebellum, whereas running rats had none in that area. Aerobic exercise and complex activity have different beneficial effects on the brain. The ideal prescription is either a sport that simultaneously taxes the cardiovascular system and the brain—tennis is a good example—or a ten-minute aerobic warm-up before something nonaerobic and skill-based, such as rock climbing or balance drills. Learning tango puts further demands on attention, judgment, and precision of movement, because you have to react to another person. Add in the fun and social aspect, and you are activating the brain and the muscles all the way down through the system.
Chapter 3 — Stress
Neurons get broken down and built up just like muscles—stressing them makes them more resilient. This is how exercise forces the body and mind to adapt. If we strip away everything else, our ingrained reaction to stress is about focusing on the danger, fueling the reaction, and logging in the experience for future reference—which can be thought of as wisdom.
The fight-or-flight response calls into action several of the body’s most powerful hormones and scores of neurochemicals in the brain. The amygdala, the brain’s panic button, sets off the chain reaction on receiving sensory input about a possible threat to the body’s equilibrium. Its job is to assign intensity to incoming information, which may or may not be obviously survival-related—it is not just about fear, but any intense emotional state, including euphoria or sexual arousal. Winning the lottery or dining with a supermodel can trigger the amygdala. Our brains do not distinguish between good and bad demands on the system; in evolutionary terms, good fortune and a good date are both related to survival. Two neurotransmitters put the brain on alert: norepinephrine arouses attention, then dopamine sharpens and focuses it. An imbalance of these neurotransmitters is why some people with ADHD come across as stress junkies—they have to get stressed to focus. It is one of the primary factors in procrastination, as people learn to wait until the deadline looms and stress finally unleashes the neurochemicals they need to sit down and do the work.
Once the alarm fires, cortisol takes over for epinephrine and signals the liver to make more glucose available in the bloodstream, while blocking insulin receptors at nonessential tissues and shuttling fuel only to areas important for fight-or-flight. The strategy is to make the body insulin-resistant so the brain has enough glucose. Cortisol also restocks energy stores by converting protein into glycogen and storing fat. If this process continues unabated, as in chronic stress, it amasses a surplus fuel supply around the abdomen in the form of belly fat. Unrelenting cortisol also explains why some marathon runners carry a slight paunch despite all their training—their bodies never get a chance to adequately recover.
Operating on a fixed budget of fuel, the brain has evolved to shift energy resources as necessary, meaning that mental processing is competitive. If one structure is active, it must come at the expense of another. One of the central problems with chronic stress is that if the HPA axis is guzzling all the fuel to keep the system on alert, the thinking parts of the brain are being robbed of energy. During acute stress, beefed-up cells cement the survival memory and shield those neurons from other demands. A neuron might be part of any number of memories, but if a potential memory comes along during stress, it has a more difficult time recruiting neurons for its own new circuit. This likely explains why memories unrelated to the stressor are blocked during the stress response—and why people with chronically high cortisol, from depression or chronic anxiety, have so much difficulty learning new material. It is not just lack of motivation; the hippocampal neurons have bolstered their glutamate machinery and shut out less important stimuli. They are obsessed with the stress. Excess cortisol can also block access to existing memories, which explains how people can forget where the fire exit is when there is actually a fire. The neurological point of fire drills is to make those circuits stronger, to burn in the memory.
The stress response is elegantly adaptive behavior, but because it does not get you very far in today’s world, there is no outlet for all that energy buildup. You have to make a conscious effort to initiate the physical component of fight or flight. The great paradox of the modern age may be that there is not more hardship, just more news—and too much of it. The twenty-four-hour streaming torrent of tragedy and demands keeps the amygdala flying. It is no wonder that obesity has doubled in the past twenty years—our lifestyle today is both more stressful and more sedentary.
Cellular stress takes two distinct forms. Metabolic stress happens when cells cannot produce adequate ATP, either because glucose cannot get into the cell or because there is not enough of it to go around. Excitotoxic stress occurs when there is so much glutamate activity that there is not enough ATP to keep up with the energy demand. If this continues without recovery, the dendrites shrink back and the cell eventually dies—neurodegeneration, the mechanism underlying diseases such as Alzheimer’s, Parkinson’s, and aging itself. Research into these diseases has revealed the body’s natural countermeasures. Mark Mattson, chief of the neurosciences lab at the National Institute on Aging, uses dietary restriction to cause mild cellular stress in his experiments and has found that mice and rats given a third of their normal calories live up to forty percent longer than average. His work has helped identify protective molecules unleashed during various types of stress, including aerobic exercise. The advantage of using exercise to inoculate the brain is that it ramps up growth factors more than other stimuli do. The best way to build up these defenses is by bringing mild stress on yourself: using the brain to learn, restricting calories, exercising, and, as Mattson would remind you, eating your vegetables.
Sometimes the fight-or-flight switch gets stuck in the on position. It can be a function of genetics: those whose parents suffered from hypertension still show elevated levels of cortisol twenty-four hours after a stressful public speaking situation. Or it can be environmental: prenatal rats whose mothers are subjected to repeated stress grow up with a lower stress threshold than their normal counterparts—they get stressed more easily, both physically and psychologically.
It is what happens after exercise that optimizes the brain. In addition to raising the fight-or-flight threshold, exercise kick-starts the cellular recovery process. It increases the efficiency of intercellular energy production, allowing neurons to meet fuel demands without increasing toxic oxidative stress. You do get waste buildup, but you also get the enzymes that chew it up, plus a janitorial service that disposes of broken bits of DNA and other by-products of normal cellular use and aging—both of which help prevent the onset of cancer and neurodegeneration. While exercise induces the stress response, if the activity level is not extreme, it should not flood the system with cortisol. The stress of exercise is predictable and controllable because you are initiating the action, and these two variables are key to psychology. With exercise you gain a sense of mastery and self-confidence. As you develop awareness of your own ability to manage stress without relying on negative coping mechanisms, you increase your ability to snap out of it. The mechanisms by which exercise changes how we think and feel are far more effective than donuts, medicines, and wine. When you say you feel less stressed after you go for a swim, or even a fast walk, you are.
Chronic stress is linked to some of our most deadly diseases. Repeated spikes in blood pressure damage vessels, plaque builds up, and atherosclerosis follows. An unchecked stress response stockpiles fat around the midsection, which studies show is more dangerous than fat stored elsewhere. A 2004 study at Leeds Metropolitan University found that workers who used their company’s gym were more productive and felt better able to handle their workloads. Among two hundred and ten participants—most taking aerobics classes at lunchtime, though some lifted weights or practiced yoga—sixty-five percent fared better on days they exercised in all three categories: interacting with colleagues, managing their time, and meeting deadlines. They also felt less fatigued in the afternoon, despite expending energy during the day. In recent years, doctors have started recommending exercise for cancer patients, both to boost the immune response and to fend off stress and depression. Activity is clearly a factor: twenty-three of thirty-five studies show an increased risk of breast cancer for inactive women; physically active people have fifty percent less chance of developing colon cancer; and active men over sixty-five have a seventy percent lower chance of developing the advanced, typically fatal form of prostate cancer. The more stress you have, the more your body needs to move to keep your brain running smoothly.
Chapter 4 — Anxiety
When you are facing an upcoming speech or a brewing confrontation with your boss, anxiety sharpens your attention so you can meet the challenge. Physical symptoms range from feeling tense, jittery, and short of breath to a racing heart, sweating, and—in the case of full-blown panic attacks—severe chest pains. Emotionally, what you feel is fear. In neurological terms, fear is the memory of danger. If you suffer from an anxiety disorder, the brain constantly replays that memory, forcing you to live inside that fear.
It all starts when the amygdala sounds the survival call, but unlike the normal stress response, in anxiety the all-clear signal is not working properly. Your cognitive processors fail to tell you there is no problem, or that the problem has passed and you can relax. One of the correlations scientists have found among people with generalized anxiety disorder is brain scans showing the area of the prefrontal cortex responsible for sending cease-and-desist signals to the amygdala as being smaller than it should be. Left unchecked, the overexcited amygdala tags too many situations as challenges to survival and burns them into memory. The fear memories form connections with each other and the anxiety snowballs. Eventually, the amygdala overwhelms attempts by the hippocampus to tone down the fight-or-flight response by putting the fear in context. As the snowball grows and more and more memories become associated with fear, your world shrinks.
A huge part of the problem with social anxiety is that the more you withdraw, the less practice you get interacting, and the scarier the prospect becomes. Just as anxiety can feed on itself, so can courage. The majority of studies show that aerobic exercise significantly alleviates symptoms of any anxiety disorder, and it helps the average person reduce normal feelings of anxiousness too. Over time, you teach the brain that the symptoms do not always spell doom and that you can survive—you are reprogramming the cognitive misinterpretation. Moving the body also triggers the release of GABA, which is the brain’s major inhibitory neurotransmitter and the primary target for most antianxiety medicines.
While you cannot erase the original fear memory, you can essentially drown it out by creating a new memory and reinforcing it. By building up parallel circuitry, the brain creates a neutral alternative to the expected anxiety, learning that everything is OK. By wiring in the correct interpretation, the trigger is disconnected from the typical response—weakening the association between, say, seeing a spider and experiencing terror and a racing heart. Scientists call it reattribution. You can force the brain to trade fear memories for neutral or positive ones through cognitive behavioral therapy, or CBT. Everyone’s initial instinct in the face of anxiety is to avoid the situation, but by doing just the opposite—engaging in what is called cognitive restructuring—we use our bodies to cure our brains.
Because anxiety brings the sympathetic nervous system into play, rapid, shallow breathing expels too much carbon dioxide, dropping the blood’s pH level and triggering an alarm from the brain stem that causes muscles to constrict even more. This is why breathing into a paper bag stops hyperventilation: it forces you to rebreathe the carbon dioxide. There is certainly nothing wrong with taking medicine, but if you can achieve the same results through exercise, you build confidence in your own ability to cope—a significant advantage not just for patients with full-blown anxiety disorders but for anyone.
Exercise works on anxiety through seven distinct pathways. First, it provides distraction—moving quite literally puts your mind on something else, and while anxious people respond well to any directed distraction, the antianxiety effects of exercise last longer and carry additional benefits. Second, it reduces muscle tension, serving as a circuit breaker that interrupts the negative feedback loop from body to brain; in 1982, researcher Herbert de Vries showed that people with anxiety have overactive electrical patterns in their muscle spindles and that exercise reduced that tension, which he called the tranquilizing effects of exercise. Third, it builds brain resources by raising serotonin and norepinephrine both in the moment and over the long term—serotonin works at nearly every junction of the anxiety circuitry, improving the prefrontal cortex’s ability to inhibit fear and calming down the amygdala itself—while also increasing GABA and BDNF, which are important for cementing alternative memories.
Fourth, exercise teaches a different outcome: because the physical symptoms of anxiety—elevated heart rate, quickened breathing—are also inherent to aerobic exercise, beginning to associate those symptoms with something positive that you initiated and can control causes the fear memory to fade. Think of it as a biological bait and switch—your mind is expecting a panic attack, but instead it ends up with a positive association. Fifth, it reroutes your circuits by activating the sympathetic nervous system through deliberate action rather than passive dread, breaking free from the amygdala’s danger-filled view and paving a safe detour. Sixth, it improves resilience: you learn you can control anxiety without letting it turn into panic, developing what psychologists call self-mastery—a powerful prophylactic against anxiety sensitivity and against the depression that can develop from anxiety. And seventh, it sets you free. People who are anxious tend to immobilize themselves, curling into a safe spot to hide from the world. Agoraphobics feel trapped in their homes, but in a sense any form of anxiety feels like a trap. The opposite of that, and the treatment, is taking action, going out and exploring, moving through the environment.
For panic disorder specifically, combining medicine with exercise can be a powerful approach. Medicine provides immediate safety, and exercise gets at the fundamentals of anxiety. Because panic disorder is so frightening, starting with medication can help flip a switch fast—but it does not necessarily lead to permanent change, and the relearning process is needed for long-term relief. For anyone who is panicky, the number-one recommendation is to exercise with somebody. It offers a sense of safety and increases serotonin immediately, just from being around another person.
One long-term study followed seven hundred children into adulthood. Of those who suffered from anxiety as children, most grew out of it. But of those who developed a mood disorder, in two-thirds of the cases the problem started as preadolescent anxiety. What is tragic is that anxiety is relatively easy to treat but often goes undiagnosed in children—the anxious kids are sitting quietly at the back of the class, terrified, and nobody notices because they are well behaved. Meanwhile, anxiety is wearing negative patterns into their brains that can become entrenched and set those children up for future problems. The farther you get from your last panic episode, the less likely you are to have another one. The same holds for any brand and any degree of anxiety. The more your life changes, the more you engage with the world, the more likely you are to put the anxiety behind you for good.
Chapter 5 — Depression
Depression is best thought of as an erosion of connections—in your life as well as between your brain cells. When elevated levels of endorphins were detected in the blood of runners, it seemed to explain the good feeling everyone got from exercise. It gave us the expression runner’s high, an extreme version of the effect. But the story of how exercise defeats depression goes far deeper than endorphins.
Nobody had done a scientifically sound head-to-head comparison of exercise and antidepressants until researchers at Duke University took up the task in 1999. In the landmark study affectionately called SMILE—Standard Medical Intervention and Long-term Exercise—James Blumenthal and his colleagues randomly divided one hundred and fifty-six patients into three groups: Zoloft, exercise, or a combination of the two. The exercise group was assigned to supervised walking or jogging at seventy to eighty-five percent of their aerobic capacity for thirty minutes, three times a week. All three groups showed a significant drop in depression, and about half of each group was completely out of the woods—in remission. Another thirteen percent experienced fewer symptoms but did not fully recover. Blumenthal concluded that exercise was as effective as medication. If everyone knew that exercise worked as well as Zoloft, it could put a real dent in the disease. Subsequent research made the case even stronger: Madhukar Trivedi, a clinical psychiatrist who directs the Mood Disorders Research Program at the University of Texas Southwestern Medical School, published a pilot study in 2006 showing that patients who were not responding to antidepressants lowered their scores on a common depression test by 10.4 points on a seventeen-point scale—a huge drop—after twelve weeks of exercise.
To understand why exercise works so powerfully, you have to look at what depression does to the brain. In 1996, Yvette Sheline of Washington University in St. Louis compared ten patients with depression to ten healthy controls and found that the hippocampus of depressed patients was up to fifteen percent smaller than that of the controls. The degree of shrinkage was directly related to the length of depression—which explained why so many patients complain of learning and memory trouble, and why mood deteriorates in Alzheimer’s, the neurodegenerative disease that begins with erosion of the hippocampus. High levels of the stress hormone cortisol kill neurons in the hippocampus. If you put a neuron in a petri dish and flood it with cortisol, its vital connections to other cells retract. Fewer synapses develop, the dendrites wither, and this communication breakdown could partly explain why a depressed brain gets locked into negative thoughts—it is recycling a negative memory because it cannot branch out to form alternative connections.
Redefining depression as a connectivity issue helps explain the wide range of symptoms. It is not just a matter of feeling empty, helpless, and hopeless; it affects learning, attention, energy, and motivation—disparate systems involving different parts of the thinking brain. Depression also shuts down the drive to sleep, eat, have sex, and generally look after ourselves on a primitive level. Psychiatrist Alexander Niculescu sees depression as a survival instinct to conserve resources in an environment void of hope—to keep still and stay out of harm’s way. It is a form of hibernation: when the emotional landscape turns wintry, our neurobiology tells us to stay inside. Except that it can last much longer than a season.
Exercise boosts BDNF at least as much as antidepressants, and sometimes more, in the hippocampus. One study showed that combining exercise with antidepressants spiked BDNF by two hundred and fifty percent. Conversely, scientists have bred mice with genes that produce fifty percent less BDNF and found that they do not respond well to antidepressants, suggesting it is a necessary ingredient for the drugs to work at all. Such mice were significantly slower to try to escape stress than their peers with normal BDNF function. What makes aerobic exercise so powerful is that it is our evolutionary method of generating the spark. It lights a fire on every level of the brain, from stoking the neurons’ metabolic furnaces to forging the very structures that transmit information from one synapse to the next.
Part of the initial recovery from depression is simply getting moving. The best kind of behavioral therapy is to go outside and take a walk. It does not require elaborate planning and does not put you into a negative spin. Physical activity is very quickly reinforcing because, before, you could not initiate anything for yourself. If your prefrontal cortex has been offline for a while, you need to reprogram it, and exercise is the perfect tool. You begin to look at the world differently, seeing trees instead of a barren wasteland. When you see yourself moving, that alone is an achievement—proof that you can help yourself. Because human beings are social animals, the ideal is to choose a form of exercise that encourages making connections and takes place outside or in some environment that stimulates the senses. Asking someone to join you and putting yourself in a new setting give newly hatched neurons a powerful reason for being; new connections need to form to represent the sensory stimulation.
Trivedi has tried to cast exercise treatment in terms the medical profession might accept by quantifying it as a dose. In a study dividing eighty depressed patients into groups of varying intensities and frequencies, the high-intensity groups burned an average of fourteen hundred calories—eight calories per pound—over the course of either three or five sessions per week and cut their depression scores in half. The low-intensity groups burned an average of five hundred and sixty calories and lowered their scores by only a third, about the same as the stretching control group—roughly equivalent to a placebo. The message is what it always is: some exercise is good, more is better. The high dose is based on public health recommendations suggesting thirty minutes of moderate aerobic activity on most days—roughly three hours per week for a hundred-and-fifty-pound person.
In some ways, exercise is even more important for prevention than for treatment. One of the first symptoms of depression, even before your mood drops to new lows, is sleep disturbance—you cannot get up, or you cannot get to sleep, or both. Then you lose your energy, then your interest. The key is to get moving immediately and not stop. Set up a schedule for a daily walk, run, jog, bike ride, or dance class. If you cannot sleep, go for a walk in the dawn light and do it every day. First see your doctor about medication and start on omega-3 supplements, which are proven to have antidepressant effects—this will, hopefully, loosen the brain lock enough to at least go for a walk. Ask for help: get a friend or family member to agree to come by every day, at the same time if possible, to escort you outside and around the block. If that is not an option and you have the means, set up a regular time with a personal trainer. Start slowly and build on it. At its core, depression is defined by an absence of moving toward anything, and exercise is the way to divert those negative signals and trick the brain into coming out of hibernation.
Chapter 6 — Attention Deficit
While it is true that people with ADHD just need to get motivated, motivation is biological. What about the child who cannot pay attention in class but can sit perfectly still for hours playing a video game? Obviously they can pay attention when they want to, right? Not exactly. Functional MRI scans reveal distinct differences in activity at the reward center—a cluster of dopamine neurons called the nucleus accumbens, which is responsible for doling out pleasure or satisfaction signals to the prefrontal cortex, providing the necessary drive or motivation to focus. The sort of stimulation that activates the reward center enough to capture the brain’s attention varies from person to person.
Paradoxically, the ability to hyperfocus is a common trait of ADHD, and it often leads people to miss the diagnosis—they cannot possibly have attention problems since they sometimes get completely absorbed in what they are reading or doing. But the glitch in the attention system is not strictly a deficit; it is more an inability to direct attention or to focus on command. A more helpful way to think of ADHD is as an attention variability disorder—the deficit is one of consistency. It is easy to get distracted in today’s world. The amount of data is doubling every few years, but our attention system was built to make sense of the surrounding environment as it existed ten thousand years ago. Experts estimate that just over four percent of American adults—thirteen million people—have ADHD, though the remaining ninety-six percent are not completely free of attention problems either. To a certain degree, everyone suffers from fleeting attention, and there are varying degrees of severity—shadow syndromes that do not necessarily meet the full diagnostic checklist.
Over the years, countless parents have offered the same observation about their ADHD children: Johnny is so much better when he is doing tae kwon do. You could substitute any of the martial arts, or any highly structured form of exercise such as ballet, figure skating, or gymnastics. Less traditional sports—rock climbing, mountain biking, whitewater paddling, and skateboarding—are also effective in the sense that they require complex movements in the midst of heavy exertion. The combination of challenging the brain and the body has a greater positive impact than aerobic exercise alone. One study from a graduate student at Hofstra University found that ADHD boys ages eight to eleven who participated in martial arts twice a week improved their behavior and performance on a number of measures compared to those on a typical aerobic exercise program—though both kinds of exercise led to dramatic improvement over nonactive controls.
There is a great deal of overlap between attention, consciousness, and movement. The attention circuits are jointly regulated by norepinephrine and dopamine, which are so similar on a molecular level that they can plug into each other’s receptors—these are the chemicals targeted by ADHD medications. The reward center needs to be sufficiently activated before it will tell the prefrontal cortex that something is worth paying attention to, and this engages the prioritizing aspect of executive function, a central component of motivation. People with ADHD favor immediate gratification over mundane tasks that will help them down the road; they are prisoners of the present. They cannot maintain focus on a long-term goal, and so it seems as though they lack drive. A failure of working memory is also why people with ADHD are terrible at keeping track of time and thus prone to procrastination—they literally forget to worry about the passing time, so they never get started on the task at hand.
This is where the attention system ties in with movement and thus exercise: the areas of the brain that control physical movement also coordinate the flow of information. The cerebellum takes up just ten percent of the brain’s volume but contains half of our neurons—a densely packed area constantly buzzing with activity. For decades it was assumed to govern only movement. But it keeps rhythm for more than motor movements: it regulates certain brain systems so they run smoothly, updating and managing the flow of information to keep it moving seamlessly. Dopamine works like transmission fluid in this system—if there is not enough of it, as in ADHD, attention cannot easily be shifted, or can only be shifted all the way into high gear.
This parallel matters for Parkinson’s disease as well. Neurologists now recommend daily exercise in the early stages of the disease to stave off symptoms. Scientists induced Parkinson’s in rats by killing the dopamine cells in their basal ganglia, then forced half of them to run on a treadmill twice a day in the ten days following the onset of the disease. The runners’ dopamine levels stayed within normal ranges and their motor skills did not deteriorate. In one human study, intensive activity improved motor ability as well as mood, and those positive effects lasted for at least six weeks after the exercise stopped.
A controversial treatment for dyslexia—which occurs in about thirty percent of ADHD patients—relies entirely on physical movements to train the cerebellum. DDAT, or dyslexia, dyspraxia, and attention treatment, is based on the theory that a disruption in the brain’s ability to coordinate movement might be responsible for eye-tracking problems and thus difficulties in learning to read and write. Most children with dyslexia perform worse than average on tests of cerebellar function. DDAT involves practicing a collection of fairly simple motor-skills drills twice a day for ten minutes. In 2003, British researchers tested the effectiveness of DDAT on thirty-five children with dyslexia and declared the results astounding: after six months, students showed significant improvement in reading and writing fluency, eye movement, cognitive skills, dexterity, and balance. Notably, within a large population of prisoners, more than eighty percent had had serious learning problems as children.
With regular exercise, you can raise the baseline levels of dopamine and norepinephrine by spurring the growth of new receptors in certain brain areas. Exercise also increases norepinephrine, and the more complex the exercise, the better: rats practicing acrobatic motor skills improved BDNF levels in the cerebellum more dramatically than those running on a treadmill. The best strategy for managing ADHD is to exercise in the morning, then take medication about an hour later—generally when the immediate focusing effects of exercise begin to wear off. Many patients find that daily exercise allows them to take a lower dose of stimulant. Beyond the exercise itself, developing what might be called militant vigilance around scheduling and structure is essential. Arranging your day and your surroundings in a way that encourages focus and accomplishment—corralling your attention through your own deliberate actions—is how the system starts working for you.
Chapter 7 — Addiction
Scientists are now characterizing behaviors such as gambling, compulsive shopping, and even overeating in the same biological terms they use to explain substance abuse. The common denominator is an out-of-control reward system, which some people are born with and some develop. By studying how dopamine works as the key messenger in the reward system, scientists have drawn a crucial distinction between liking something and wanting it. As behavioral neuroscientist Terry Robinson of the University of Michigan explains, liking refers to the actual experience of pleasure, while wanting is the motivational state—the willingness to work for rewards. Dopamine is involved in wanting, but not in liking.
Typically, when you learn something, the connections stabilize and dopamine levels tail off over time. With addiction, especially drug addiction, dopamine floods the system with each use, reinforcing the memory and pushing other stimuli further into the background. Animal studies show that drugs such as cocaine and amphetamine make the dendrites in the nucleus accumbens bloom, increasing their synaptic connections. These changes can remain months and maybe even years after the drugs are stopped, which is why relapse is so easy. If you continually subject your brain to a dopamine overload, the number of receptors dwindles—so the more drugs you take, the more you need to feel the same rush. The same is true of overeating.
Imaging studies have shown that the prefrontal cortex does not fully develop until well into our twenties, which could explain why most people who experiment with drugs and get hooked do so as teenagers or in early adulthood, when their inhibition has not fully developed. As Robinson puts it, they end up with a hypersensitive system that wants drugs, and they make very bad decisions. Exercise was a conduit for shifting focus to a more productive life for many patients, and that is how it should be understood: as a way of offsetting the hopelessness and uselessness that many drug users feel. The routine and physical activity get the brain engaged and the mind moving in a direction other than toward the drug, reprogramming the basal ganglia to wire in an alternative reflexive behavior. In giving someone in recovery access to exercise, you are presenting them with something most have never had—the goals of exercise, the feeling of exercise, the challenge of it, the pleasure and the pain, the accomplishment, the physical well-being, the self-esteem. All that exercise gives us suddenly becomes a very compelling option.
Exercise fights the urge to smoke because in addition to smoothly increasing dopamine, it lowers anxiety, tension, and stress levels—the physical irritability that makes quitting so difficult. Exercise can fend off cravings for fifty minutes and double or triple the interval to the next cigarette. The fact that exercise sharpens thinking also comes into play, because one of the withdrawal symptoms of nicotine is impaired focus. People are more impulsive when they feel lousy, and both strength training and aerobic exercise decrease symptoms of depression in recovering alcoholics and smokers who have quit.
Self-regulation is a resource that can be depleted but also recharged like a muscle—and the more you use this faculty, the stronger it gets. Exercise is by far the best form of self-regulation we have. Thirty minutes of vigorous aerobic exercise five days a week is the bare minimum if you want to root out an addiction. To begin, it is best to do something every day, because the exercise will keep you occupied and focused on something positive. If you are unemployed, having exercise in place is especially essential—many people bury themselves in addiction when they lose their jobs. While morning exercise is often the best general prescription, if your goal is to break an evening habit such as having a drink every night when you come home, exercising in the evening is probably a better strategy—use the aerobic shot for a different kind of buzz. If you have not been in the habit of exercising, joining a gym or hiring a personal trainer can help, because spending the money is a strong motivator. For a food addiction, even a quick walk around the block, a few minutes with a jump rope, or a set of jumping jacks can snap your mind out of the cycle of thinking about the reward.
Chapter 8 — Hormonal Changes
”The week before my period I have to do an hour of cardio four days a week or I can’t stand myself.” That simple confession captures something millions of women experience but rarely see named in clinical terms: exercise is not optional for hormonal health, it is central to it.
German researchers decided to test whether exercise would have any impact on the painful process of labor by bringing a stationary bicycle into the labor suite. They found fifty women who agreed to pedal for periods of twenty minutes, rate their pain levels, and have their blood tested for endorphins right up until they gave birth. Eighty-four percent of them said contractions were less painful during exercise than at rest, and their ratings were inversely proportional to endorphin levels. The researchers concluded that exercising on a bicycle during labor is safe for the fetus, a stimulus to uterine contractions, and a source of analgesia.
For ten to fifteen percent of new mothers, everything seems fine at first—and then postpartum depression strikes, and it can stick around for a year or more. Exercise may be even more effective for new mothers experiencing depression than for the general population because it normalizes neurotransmitter levels. Women over sixty-five who reported higher levels of physical activity were fifty percent less likely than their inactive peers—women and men alike—to develop any form of dementia. The best type of aerobic activity is whatever is going to allow you to build it into your lifestyle.
The advice that surprises people the most is that it is important to keep up exercise during pregnancy—a recommendation now endorsed by the American College of Obstetricians and Gynecologists, which specifies thirty minutes of moderate-intensity aerobic activity every day during pregnancy for healthy women. It is important to get clearance directly from your obstetrician, but it is safe for most women. Equally important is picking up your routine as soon as possible after the baby is born, ideally within a few weeks. Although it seems contradictory, moving will actually reduce fatigue, and for women who develop postpartum depression it melts away anxiety and depression. When women are younger, one of the big motivations to exercise is to stay trim, and that is fine—use whatever gets you going. But the message to carry forward is that even as your body changes, exercise will keep your mind firm and taut. In this state of mental fitness, you will be well equipped to handle the hormonal fluctuations that every woman experiences throughout her life.
Chapter 9 — Aging
The average seventy-five-year-old suffers from three chronic medical conditions and takes five prescription medicines, according to the Centers for Disease Control. Among those over sixty-five, most suffer from hypertension; more than two-thirds are overweight; and nearly twenty percent have diabetes, which triples the chance of developing heart disease. The leading killers—heart disease, cancer, and stroke—together account for sixty-one percent of all deaths in this age group. As neuroscientist Mark Mattson of the National Institute on Aging sees it, the good news—if we take it seriously—is that many of the same factors that reduce our risk for cardiovascular disease and diabetes also reduce the risk for age-related neurodegenerative disorders. Running to lower your blood pressure also keeps the capillaries in the brain from collapsing or corroding. Lifting weights to prevent osteoporosis releases growth factors that make dendrites bloom. Omega-3 fatty acids taken for mental acuity also strengthen your bones. The mental and physical diseases of old age are tied together through the cardiovascular and metabolic systems—which explains why obese people are twice as likely to suffer from dementia, and why those with heart disease are at far greater risk of Alzheimer’s.
Paradoxically, Mattson notes, it is good that cells be periodically subjected to mild stress because it improves their ability to cope with more severe stress. Exercise is preventive medicine as well as an antidote. Age happens—there is nothing you can do about the why, but you can do something about the how and the when. The hormones estrogen in women and testosterone in men decrease with age, leading to shifts in mood or a loss of vigor and interest. Depression is a risk factor for dementia because of its corrosive effects on the hippocampus: if cortisol stays elevated, it eats away at synapses. A study from the Rush Alzheimer’s Disease Center found that people who feel lonely—those who identify with statements such as “I miss having people around” or “I experience a general sense of emptiness”—are twice as likely to develop Alzheimer’s. Exercise reduces depression and is even better than Zoloft at keeping people from relapsing.
There are nine specific ways exercise keeps you going as you age. It strengthens the cardiovascular system: a strong heart and lungs reduce resting blood pressure, putting less strain on the vessels of the body and brain. It regulates fuel, increasing levels of insulin-like growth factor, or IGF-1, which regulates insulin in the body and improves synaptic plasticity in the brain; by drawing down surplus fuel, exercise also bolsters BDNF, which is reduced by high glucose. It reduces obesity—body fat has its own nasty effects on the brain beyond its damage to the cardiovascular and metabolic systems, and exercise counteracts obesity on two fronts by burning calories and reducing appetite. It elevates your stress threshold, combating the corrosive effects of too much cortisol and bolstering neurons against excess glucose, free radicals, and the excitatory neurotransmitter glutamate, while making proteins that fix damage and delay the process. It lifts your mood, with more neurotransmitters, neurotrophins, and connectivity shoring up the hippocampus against the atrophy of depression and anxiety, while staying mobile keeps you involved with people and helps you make new friends.
It boosts the immune system: the most consistent risk factor for cancer is lack of activity, and exercise brings the immune system back into equilibrium so it can stop chronic inflammation and combat disease. It fortifies your bones: more women die from hip fractures every year than from breast cancer, and women reach peak bone mass around thirty and lose about one percent per year until menopause, when the pace doubles—calcium, vitamin D, and weight-bearing exercise or strength training counteract this loss. It boosts motivation, counteracting the natural decline of dopamine in the motivation and motor systems, strengthening connections between dopamine neurons while guarding against Parkinson’s; it is important to have plans and goals and appointments, which is why sports such as golf and tennis are great. And it fosters neuroplasticity, which is the best way to guard against neurodegenerative diseases—aerobic exercise strengthens connections between brain cells, creates more synapses to expand the web of connections, and spurs newly born stem cells to become functional neurons in the hippocampus.
The one proven way to live longer, at least in lab rodents, is to consume fewer calories: mice and rats given thirty percent fewer calories live up to forty percent longer than animals allowed to eat as much as they want. For the rest of us, the practical program looks like this. Walking is perfectly adequate for your aerobic base—do it outside with a friend if possible, and find something you will enjoy over the long haul. Try a more intense pace for two days a week, at seventy to seventy-five percent of your maximum heart rate, for twenty to thirty minutes; if you have not been exercising, build up to this speed, and that is fine. Consistency is probably more important than intensity. Hit the weights or resistance machines twice a week, doing three sets at weights that allow ten to fifteen repetitions per set—a Tufts University study of women fifty to seventy years old showed that those who participated in strength training for a year added one percent of bone density in their hips and spine, while the sedentary group lost two-and-a-half percent. Focus on balance and flexibility twice a week for thirty minutes or so; yoga, Pilates, tai chi, martial arts, and dance all involve skills important to staying agile. And volunteer—it involves social contact, which is inherently challenging for the brain. Anything that keeps you in contact with other people helps you live better and longer; statistics show a tight inverse relationship between sociability and mortality. Novel experiences demand more from your brain and build its ability to compensate. You get more Miracle-Gro, more connections, more neurons, and more possibilities.
Chapter 10 — The Regimen
The point this book has tried to make—that exercise is the single most powerful tool you have to optimize your brain function—is based on evidence gathered from hundreds and hundreds of research papers, most of them published only within the past decade. Body and brain are connected. Why not take care of both?
The most important thing is to do something, and to start. For the sedentary—especially if inactivity is due to depression—taking that first step may seem impossible. Some people face a genuine catch-22: they cannot start because they do not have the energy, and they do not have the energy because they are not exercising. This is a very real problem, not simply an issue of willpower. The key is to attack the business of starting as a challenge in itself. It is also crucial to build in recovery time, so your body and brain have the opportunity to bounce back and the adaptations have a chance to stick.
One of the key differences between moderate and high-intensity exercise is that once you get closer to your maximum—and especially when you get into the anaerobic range—the pituitary gland unleashes human growth hormone, or HGH. This is what life-extension groups call the fountain of youth. HGH levels naturally secreted into the bloodstream decrease over your life span, dwindling to a tenth of childhood levels by middle age, and a sedentary lifestyle exacerbates this decline—high levels of cortisol, insulin resistance, and excess fatty acids in the bloodstream all clamp down further on the hormone’s release. HGH is the body’s master craftsman: it burns belly fat, layers on muscle fiber, and pumps up brain volume. Researchers believe it can reverse the loss of brain volume that naturally occurs as you age. Athletes such as Olympic sprinters and football players are essentially spiking their levels of HGH when they do interval training—doping the natural way.
High-intensity exercise toughens you up both physiologically and psychologically. But you do not need to go to extremes to reap the rewards. A single thirty-second sprint on a stationary bike generated a sixfold increase in HGH, peaking two hours after the sprint, in a study from the University of Bath. Neurologists at the University of Muenster reported that interval training improves learning ability: during a forty-minute treadmill run, volunteers who did two three-minute sprints separated by two minutes at lower intensity showed significantly higher increases in BDNF as well as norepinephrine compared to subjects who stayed at low intensity. Even doing squats doubled HGH levels compared with running at high intensity for thirty minutes. Every day is best, but even intermittent exercise works wonders.
Finding the right social context can be the key to sticking with it. For some adults, being part of a team gets them hooked—whether it is a city basketball program, an adult soccer league, or Masters swimming. Maybe walking with the one you love will turn out to be the answer, or maybe you have always wanted to learn tae kwon do, or maybe you will discover a passion for the infinite challenge of rock climbing. The point is cooperation over competition, and finding the activity that makes you want to come back. What the teachers at Naperville built—a culture of movement and understanding rather than performance and fear—is the template. Exercise is not the punishment at the end of a bad day. It is the most powerful thing you can do for the organ running your life. Lace up your shoes.