The lifelong mental benefits of exercising have long been known, from improving learning in kids to staving off dementia in seniors. Yet how working up a sweat leads to better cognition is much less clear. A study in the Journal of Applied Physiology reveals that the key may lie in the body’s power supply.

Just as a booming metropolis might build new power plants to meet a rising need for electricity, our muscles respond to the demands of exercise by producing new mitochondria, the tiny structures inside cells that supply the body with energy. J. Mark Davis, a physiolo-

gist at the University of South Carolina, and his colleagues wondered if brain cells might do the same thing. While studying mice, they found that quantities of a signaling molecule, dubbed by researchers “a master regulator” of mitochondria production, increased in the brain after half an hour a day of treadmill running. The mice’s brain cells also had more mitochondrial DNA—distinct from the regular cellular DNA found in the nucleus—providing “gold standard” evidence of more mitochondria. It appears that the brain “adapts and changes by bringing more of these power­houses” online, Davis says. The increased energy supply allows the brain to work faster and more efficiently.

The finding could help scientists understand how exercise staves off age- and disease-related declines in brain function, because neurons naturally lose mito­chondria as we age, Davis explains. Although past research has shown that exercise encourages the growth of new neurons in certain regions, the widespread expansion of the energy supply could underlie the benefits of exercise to more general brain functions such as mood regulation and dementia pre­vention. “The evidence is accumulating rapidly that exercise keeps the brain younger,” Davis says.