It is never too late for the lazy and the old to get off their haunches and exercise. This week, a study found that physical activity beginning in old age, even after a whole life lost to sloth, can help rescue the brain from mental decline-at least in mice. The link between taking exercise and remaining mentally astute into the golden years is well known but not well understood. Exercise seems to stimulate the growth of new neurons in certain parts of the brain. Physically active animals (including humans) perform better on tests of cognition than their inactive counterparts. But the assumption was that, at some point, people might be past salvaging.
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