Can Exercise Make You Smarter?

Descartes is turning over in his grave: the mind and body grow more intertwined by the day. It's becoming clear that maintaining a healthy mind into old age isn't simply a matter of keeping the brain active with card games and crossword puzzles. Perhaps equally important is an active body. Physical exercise is a crucial part of mental health:

Researchers are realizing that the mental effects of exercise are far more profound and complex than they once thought. The process starts in the muscles. Every time a bicep or quad contracts and releases, it sends out chemicals, including a protein called IGF-1 that travels through the bloodstream, across the blood-brain barrier and into the brain itself. There, IGF-1 takes on the role of foreman in the body's neurotransmitter factory. It issues orders to ramp up production of several chemicals, including one called brain-derived neurotrophic factor, or BDNF. Ratey, author of the upcoming book "Spark: The Revolutionary New Science of Exercise and the Brain," calls this molecule "Miracle-Gro for the brain." It fuels almost all the activities that lead to higher thought.

Obviously, BDNF really isn't Miracle-Gro for the brain. There's no such thing. But BDNF has been implicated in several important aspects of brain function. For starters, BDNF is repressed in response to stress. (After a stressful event, the brain releases glucocorticoids, which seem to repress BDNF.) Reduced levels of BDNF have also been implicated in depression, and it's now thought that one of the mechanisms of action of anti-depressants is to raise cortical levels of BDNF. Finally, high levels of BDNF also up-regulate the mechanisms underlying plasticity and neurogenesis. (This is why stress reduces neurogenesis.)

So it's a pretty convoluted chemical pathway - IGF-1 upregulates BDNF which might upregulate plasticity which might upregulate happiness and intelligence - but the evidence is certainly suggestive. But get some exercise anyways: even if it doesn't make you smarter, it's still good for your body.

PS. Does this quote make any sense?

"Dopamine, serotonin, norepinephrine--all of these are elevated after a bout of exercise," says Ratey. "So having a workout will help with focus, calming down, impulsivity--it's like taking a little bit of Prozac and a little bit of Ritalin."

I mean, cocaine also increases the release of dopamine and serotonin, but we don't say that crack makes us smarter. I find the BDNF and exercise story much more convincing than the more generic "exercise increases neurotransmitter release" story. Lots of things increase neurotransmitter release, and they aren't necessarily good for us.