Spark: The Revolutionary New Science of Exercise and the Brain

by John J. Ratey

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A memory, scientists believe, is a collection of information fragments dispersed throughout the brain. The hippocampus serves as a way station, receiving the fragments from the cortex, and then bundling them together and sending them back up as a map of a unique new pattern of connections. Brain scans show that when we learn a new word, for example, the prefrontal cortex lights up with activity (as does the hippocampus and other pertinent areas, such as the auditory cortex). Once the circuit has been established by the firing of glutamate, and the word is learned, the prefrontal cortex goes dark. It has overseen the initial stages of the project, and now it can leave the responsibility to a team of capable employees while it moves on to new challenges.

“We developed the first films and, son of a gun, it showed up in the hippocampus. Well, the significance is that the hippocampus is an area of the brain that is extremely vulnerable to degenerative disease and that is needed for learning. Instantly I said, This changes the game completely.”

Among those with the least cognitive decline over a four-year period, three factors turned up: education, self-efficacy, and exercise.

Unlike humans, rodents seem to inherently enjoy physical activity, and Cotman’s mice ran several kilometers a night. They were divided into four groups: mice running for two, four, or seven nights, and one control group with no running wheel. When their brains were injected with a molecule that binds to BDNF and scanned, not only did the scans of the running rodents show an increase in BDNF over controls, but the farther each mouse ran, the higher the levels were. When Cotman saw the results—that the spike occurred in the hippocampus—he didn’t believe them himself: “I said, No, c’mon guys, we did something wrong; the darn hippocampus is lit up. We had to repeat the experiment—it was too far out. And so we did, and we got the same results.”

Indeed, in a 2007 study of humans, German researchers found that people learn vocabulary words 20 percent faster following exercise than they did before exercise, and that the rate of learning correlated directly with levels of BDNF.

BDNF gives the synapses the tools they need to take in information, process it, associate it, remember it, and put it in context.

As we age, production of all three of these factors and BDNF naturally tails off, bringing down neurogenesis with it. Even before we get old, however, a drop in these factors and in neurogenesis can show up in stress and depression, as we’ll see later. To me, this is actually encouraging news, because if moving the body increases BDNF, IGF-1, VEGF, and FGF-2, it means we have some control over the situation.

Cognitive flexibility is an important executive function that reflects our ability to shift thinking and to produce a steady flow of creative thoughts and answers as opposed to a regurgitation of the usual responses. The trait correlates with high-performance levels in intellectually demanding jobs. So if you have an important afternoon brainstorming session scheduled, going for a short, intense run during lunchtime is a smart idea.

What I would suggest, then, is to either choose a sport that simultaneously taxes the cardiovascular system and the brain—tennis is a good example—or do a ten-minute aerobic warm-up before something nonaerobic and skill-based, such as rock climbing or balance drills.

The more complex the movements, the more complex the synaptic connections. And even though these circuits are created through movement, they can be recruited by other areas and used for thinking. This is why learning how to play the piano makes it easier for kids to learn math. The prefrontal cortex will co-opt the mental power of the physical skills and apply it to other situations.

Learning the asanas of yoga, the positions of ballet, the skills of gymnastics, the elements of figure skating, the contortions of Pilates, the forms of karate—all these practices engage nerve cells throughout the brain. Studies of dancers, for example, show that moving to an irregular rhythm versus a regular one improves brain plasticity.

Humans are unique among animals in that the danger doesn’t have to be clear and present to elicit a response—we can anticipate it; we can remember it; we can conceptualize it. And this capacity complicates our lives dramatically. “The mind is so powerful that we can set off the [stress] response just by imagining ourselves in a threatening situation,” writes Rockefeller University neuroscientist Bruce McEwen in his book The End of Stress as We Know It. In other words, we can think ourselves into a frenzy.

An imbalance of these neurotransmitters is why some people with attention-deficit/hyperactivity disorder (ADHD) come across as stress junkies. They have to get stressed to focus. It’s one of the primary factors in procrastination. People learn to wait until the Sword of Damocles is ready to fall—it’s only then, when stress unleashes norepinephrine and dopamine, that they can sit down and do the work. A need for stress also explains why ADHD patients sometimes seem to shoot themselves in the foot.

Cortisol also begins restocking the shelves, so to speak, replenishing energy stores depleted by the action of epinephrine. It converts protein into glycogen and begins the process of storing fat. If this process continues unabated, as in chronic stress, the action of cortisol amasses a surplus fuel supply around the abdomen in the form of belly fat.

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 to be part of its own new circuit. It needs to clear a certain threshold to make an impression.

The stress response is elegantly adaptive behavior, but because it doesn’t get you very far in today’s world, there’s no outlet for all that energy buildup. You have to make a conscious effort to initiate the physical component of fight or flight.

The cellular stress-and-recovery dynamic takes place on three fronts: oxidation, metabolism, and excitation.

A surplus of glutamate also causes physical damage to the hippocampus. The neurotransmitter acts by allowing electron-snatching calcium ions into the cell, and they create free radicals. Without enough antioxidants on patrol, the free radicals punch holes in the walls, and the cell can rupture and die.

While chronic stress is bullying the hippocampus—pruning its dendrites, killing its neurons, and preventing neurogenesis—the amygdala is having a field day. The stress overload creates more connections in the amygdala, which keeps firing and calling for cortisol, even though there’s plenty of the hormone available, and the negative situation feeds on itself. The more the amygdala fires, the stronger it gets. Eventually the amygdala takes control of its partnership with the hippocampus, repressing the context—and thus the connection to reality—and branding the memory with fear. The stress becomes generalized, and the feeling becomes a free-floating sense of fear that morphs into anxiety. It’s as if everything is a stressor, and this colors perception and leads to even more stress. “The animal becomes more anxious even while its cognitive skills are being eroded,” says McEwen.

As McEwen writes in The End of Stress as We Know It, “It’s not inevitable or normal for the very system designed to protect us to become a threat in itself.”

The common denominator is irrational dread.

Some people also have anxiety sensitivity, which complicates any form of the disorder. Your heart rate or breathing might increase for an unrelated reason, and when you sense this physical arousal, that awareness alone can trigger a state of anxiety or panic. You lose control because you feel like you’re going to lose control. If you begin to fear the fear—whether it’s mental or physical—anxiety can quickly spiral out of control. Amy is a textbook case of generalized anxiety disorder, with shades of panic disorder and social anxiety disorder. She displays both the state—hyperalert, tense, expecting the worst—and the trait, which is the deeper, more ingrained tendency to slip into the state.

Gradually, she got into a routine, logging thirty minutes every morning. She had very little she could enjoy during this period, but she started having fun with the exercise. She described how she incorporated upper-body twists while pumping away on the trainer, and she followed her aerobic session with an hour of yoga (which has been proven to reduce anxiousness). She was gaining a sense of control over her state of anxiety, a vital step toward conquering the trait. She quickly learned that if she became anxious or panicky at home, she could jump on the elliptical for ten or fifteen minutes to quell the feelings on the spot (in the same way my patient Susan used her jump rope to cope with stress).

The truth is, her situation hasn’t changed all that much—just her response to it and thus her attitude.

Her strategy has noticeably lowered her anxiety sensitivity, which allows the brain to learn its way out of the trap.

Only the high-intensity group felt less afraid of the physical symptoms of anxiety, and this distinction started to show up after just the second exercise session. The theory is that when we increase our heart rate and breathing in the context of exercise, we learn that these physical signs don’t necessarily lead to an anxiety attack. We become more comfortable with the feeling of our body being aroused, and we don’t automatically assume that the arousal is noxious.

Feels a lot like exposure therapy

This is a key finding given the notion of anxiety as a cognitive misinterpretation. By using exercise to combat the symptoms of anxiety, you can treat the state, and as your level of fitness improves, you chip away at the trait. Over time, you teach the brain that the symptoms don’t always spell doom and that you can survive; you’re reprogramming the cognitive misinterpretation.

Moving the body also triggers the release of gammaamino-butyric acid (GABA), which is the brain’s major inhibitory neurotransmitter (and the primary target for most of our antianxiety medicines). Having normal levels of GABA is crucial to stopping, at the cellular level, the self-fulfilling prophecy of anxiety—it interrupts the obsessive feedback loop within the brain. And when the heart starts beating hard, its muscle cells produce a molecule called atrial natriuretic peptide (ANP) that puts the brakes on the hyperaroused state. ANP is another tool the body uses to regulate the stress response, which I’ll explain more later.

Anxiety is fear, but what is fear? In neurological terms, fear is the memory of danger. If we suffer from an anxiety disorder, the brain constantly replays that memory, forcing us to live in that fear.

Like most people with social anxiety, she felt on display, terrified that she would do something embarrassing or humiliating. Afterward, she would go home and berate herself for her “performance.”

In the experiment, mice with the mutant BDNF gene that were put in an anxiety-provoking situation didn’t get the relief they should have from Prozac. The antidepressant worked fine for normal mice under the same circumstances. This suggests that BDNF might be an essential ingredient in combating anxiety, probably because it helps wire in positive memories that create a detour around the fear. I

In a six-month follow-up, the exercise patients who were the most fit had the lowest anxiety scores. In the end, the exercise group landed in the same healthy place as the clomipramine group, and they did so of their own accord. There’s 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. This is a significant advantage not just for patients with full-blown anxiety disorders, but for anyone.

called fear extinction. While we can’t erase the original fear memory, we can essentially drown it out by creating a new memory and reinforcing it. By building up parallel circuitry to the fear memory, 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.

cognitive behavioral therapy (CBT). Studies show that CBT is about as effective as SSRIs in treating anxiety, although varied results suggest that the quality of the therapy is crucial. The strategy is to expose the patient to the source of fear in small doses in the company of the therapist. When we experience the symptoms without the panic, the brain goes through a cognitive restructuring. We build connections in the prefrontal cortex that help calm the amygdala, which makes us feel safe, and then the brain records a memory of that feeling. When we add in exercise, we get the neurotransmitters and neurotrophic factors bolstering the circuits between the prefrontal cortex and the amygdala, providing further control and creating a positive snowball effect.

Conquering Depression and Anxiety through Exercise,

“In essence,” he writes, his approach is a matter of “getting back on the horse that threw you.” Teaching the brain that we can survive is crucial to overcoming the anxiety.

in humans, simply by taking action we’re circumventing the mechanism for the fear memory. The basal nucleus is the action pathway, and we can even spark it with thought. For one of my patients, who was traumatized by losing both his job and his girlfriend, I suggested that he start each day by getting to the gym, to keep from stewing in the trauma. He could also shift the flow from fear to action circuits by making a list of potential employers to call—a more classic example of active coping—but it wouldn’t affect the brain as broadly.

1. It provides distraction.

2. It reduces muscle tension.

3. It builds brain resources.

4. It teaches a different outcome.

5. It reroutes your circuits.

6. It improves resilience.

7. It sets you free.

I told the young man that the A-number-one thing he needed to do was exercise with somebody. That goes for anyone who is panicky. It offers a sense of safety, but it also increases levels of serotonin immediately, just from being around another person. In his case, I suggested that he exercise at home, or close to it, until he started to associate his elevated heart rate with a positive experience. He needed to find a type of exercise he enjoyed, and, because his panic seemed to have a strong genetic component, I told him he’d really have to work at it. He’d have to start doing at least fifteen minutes of rigorous aerobic exercise a day—running, swimming, biking, rowing, or whatever would get his heart pounding. Intensity was particularly important in his case because of the evidence that only rigorous exercise alleviates sensitivity to the physical arousal of anxiety.

In Britain, doctors now use exercise as a first-line treatment for depression, but it’s vastly underutilized in the United States, and that’s a shame. According to the World Health Organization, depression is the leading cause of disability in the United States and Canada, ahead of coronary heart disease, any given cancer, and AIDS. About 17 percent of American adults experience depression at some point in their lives, to the tune of $26.1 billion in health care costs each year.

Researchers tracked 8,023 people for twenty-six years, surveying them about a number of factors related to lifestyle habits and healthiness starting in 1965. They checked back in with the participants in 1974 and in 1983. Of all the people with no signs of depression at the beginning, those who became inactive over the next nine years were 1.5 times more likely to have depression by 1983 than their active counterparts. On the other hand, those who were inactive to begin with but increased their level of activity by the first interval were no more likely to be depressed by 1983 than those who were active to begin with. In other words, changing your exercise habits changes your risk for depression.

A Finnish study of 3,403 people in 1999 showed that those who exercise at least two to three times a week experience significantly less depression, anger, stress, and “cynical distrust” than those who exercise less or not at all.

Another study, from the epidemiology department at Columbia University published in 2003, surveyed 8,098 people and found the same inverse relationship between exercise and depression.