Can exercise make the brain more fit? That absorbing question inspired a new study at the University of South Carolina during which scientists assembled mice and assigned half to run for an hour a day on little treadmills, while the rest lounged in their cages without exercising.
Earlier studies have shown that exercise sparks neurogenesis, or the creation of entirely new brain cells. But the South Carolina scientists were not looking for new cells. They were looking inside existing ones to see if exercise was whipping those cells into shape, similar to the way that exercise strengthens muscle.
For centuries, people have known that exercise remodels muscles, rendering them more durable and fatigue-resistant. In part, that process involves an increase in the number of muscle mitochondria, the tiny organelles that float around a cell’s nucleus and act as biological powerhouses, helping to create the energy that fuels almost all cellular activity. The greater the mitochondrial density in a cell, the greater its vitality.
Past experiments have shown persuasively that exercise spurs the birth of new mitochondria in muscle cells and improves the vigor of the existing organelles. This upsurge in mitochondria, in turn, has been linked not only to improvements in exercise endurance but to increased longevity in animals and reduced risk for obesity, diabetes and heart disease in people. It is a very potent cellular reaction.
Brain cells are also fueled by mitochondria. But until now, no one has known if a similar response to exercise occurs in the brain.
Like muscles, many parts of the brain get a robust physiological workout during exercise. “The brain has to work hard to keep the muscles moving” and all of the bodily systems in sync, says J. Mark Davis, a professor of exercise science at the Arnold School of Public Health at the University of South Carolina and senior author of the new mouse study, which was published last month in The Journal of Applied Physiology. Scans have shown that metabolic activity in many parts of the brain surges during workouts, but it was unknown whether those active brain cells were actually adapting and changing.