Previous studies found that fitter kids generally scored better on such tests. And in this case, too, those children performed better on the tests. But the M.R.I.’s provided a clearer picture of how it might work. They showed that fit children had significantly larger basal ganglia, a key part of the brain that aids in maintaining attention and “executive control,” or the ability to coordinate actions and thoughts crisply. Since both groups of children had similar socioeconomic backgrounds, body mass index and other variables, the researchers concluded that being fit had enlarged that portion of their brains.
Meanwhile, in a separate, newly completed study by many of the same researchers at the University of Illinois, a second group of 9- and 10-year-old children were also categorized by fitness levels and had their brains scanned, but they completed different tests, this time focusing on complex memory. Such thinking is associated with activity in the hippocampus, a structure in the brain’s medial temporal lobes. Sure enough, the M.R.I. scans revealed that the fittest children had heftier hippocampi.