If you’re over 50, you need exercise to stay fit–no disputing that. But what are you doing to keep your brain lean and mean? The concept of brain fitness has caught fire lately. “It’s as simple as ‘use it or lose it,'” says Nancy Merz Nordstrom., director of the Elderhostel Institute Network. “If we want to do everything possible to keep our whole being alert, vibrant and connected as we age, we have to continue to challenge ourselves.” A growing body of brain research suggest that the brain’s physical anatomy responds to learning by regenerating brain cells. The benefits include enhanced mental alertness, thought processes, response times and reflexes.