How do octogenarians like Gloria Vanderbilt and Justice John Paul Stevens stop the effects of aging? Those two are prolific and active despite their ages. A new study finds that the best way to avoid mental decline is to always keep your brain active with physical and mental exercises. The study, published in the journal "Neurology," found that older people that were not overweight, didn't smoke, had a good education, and active social lives held steady on intellectual tests—and some even improved. As it turns out, all those advertisements for brain-boosting puzzles, DVDs and software aren't the cure-alls they claim to be.