Mental activity is key to healthy brain aging, from the Harvard Men's Health Watch

What's the best way to maintain mental skills and memory power as you get older? Just as exercise and physical activity prompt muscles to grow stronger, mental exercise keeps thinking skills and memory in tone, according to the November 2012 Harvard Men's Health Watch.

Does playing solitaire or Angry Birds qualify as mental exercise? "If it's too easy, it's not helping you," explains Dr. Anne Fabiny, chief of geriatrics at Cambridge Health Alliance and an assistant professor of medicine at Harvard Medical School.