When I'm in a blue funk, going for a run helps me feel a lot better. And prolonged periods of inactivity—say, after a big race—make me anxious, and something close to depressed. There are certainly a host of reasons why exercise seems to improve my mood (the Justin Timberlake on my iPod and the view from the Brooklyn Bridge, for example), but one potential factor is the idea, supported by a growing body of research, that physical exertion itself has a much bigger influence on the brain than previously thought. Just this week, a survey of existing research published by the Cochrane Library concluded that the same aerobic exercise that is good for your heart also improves cognitive function—specifically, motor function, auditory attention, and memory—in healthy older adults.
That's only one piece of what has become a burgeoning field. In Spark: The Revolutionary New Science of Exercise and the Brain, published earlier this year, psychiatrist John Ratey explores the neuroscience behind potential beneficial effects of aerobic exercise on anxiety, stress, depression, learning, aging, and even attention deficit disorder. (Research hasn't as fully explored the effects of anaerobic exercise or more passive activities like stretching and yoga.) "Even people who are overweight and who start exercising see improvements in mood and cognition in as little as 12 weeks," he says. One study found that exercise improved depression symptoms as well as medication.
A host of mechanisms are thought to be responsible. As U.S. News reported earlier this year in a story about keeping your brain fit, studies in rodents showed that running led to an increase in new brain cells in a part of the brain called the hippocampus that plays a large role in learning and memory. Researchers don't count brain cells in studies of live humans, but one study of regularly exercising adults did show increased blood flow to the same area. Because of the obvious implications for age-related memory lapses and dementia, much of the human research in this area has been in the elderly, says Henriette van Praag, a researcher in the neuroplasticity and behavior unit in the laboratory of neurosciences at the National Institute on Aging. She's now studying (in rodents) whether the progression of neurodegenerative diseases like Alzheimer's can be slowed by exercise.
Some studies have looked at kids. They haven't yet shown that getting exercise causes improvements in concentration and learning, but "what we agree on at this point is that there's a strong association between aerobic fitness and performance on standardized testing, grades, and other measures of cognitive performance," says Darla Castelli, a researcher in the department of kinesiology and community health at the University of Illinois-Urbana-Champaign. She was an investigator on a study published last year in the Journal of Sport & Exercise Psychology that looked at the relationship between physical fitness and academic performance in 259 third and fifth graders. Aerobic exercise (as well as BMI) was related to achievement in reading and math. Now she's preparing to start a study in August that will compare cognition in a group of kids who participate in an after-school physical activity program with a group that does not.
Chemicals influenced by exercise, including neurotransmitters and growth factors, are being investigated for their role in mood and brain function. Even runner's high, that elusive euphoria that some people experience after prolonged or intensive running, is becoming clearer—literally. A study done in Germany, published in March in Cerebral Cortex, used PET scans to look at the brains of 10 athletes following a two-hour run. The scans confirmed that during the run, endorphins were released in certain parts of the brain known to be involved with the processing of emotions. But while endorphins may cause the runner's high, they're not the sole regulators of mood and emotions during a workout. "A lot of things contribute to us feeling better when we exercise," says Ratey. "Endorphins are one of them, but so are norepinephrine, serotonin, dopamine, and brain-derived neurotrophic factor (BDNF)."
So you're sold. How much do you need to work out to get these fabulous brain benefits? "Something is better than nothing," says Ratey. As little as 10 minutes of brisk walking can quench the urge for a cigarette for over an hour, he says, and Castelli notes that a single 10-minute bout of physical activity in an academic setting boosts attention and problem-solving skills in kids. A study published online earlier this month in the British Journal of Sports Medicine found that mental health benefits were observed after 20 minutes of physical activity, though the more exercise and higher intensity, the better the effects. Which means that doing the recommended 30 minutes a day of aerobic activity will cover your brain as well as your heart.