TRUDEAU: And people who exercised had larger hippocampi, a critical memory center. Other brain areas, too central for decision-making, planning and multi-tasking were also larger, larger than when they began the aerobic exercise program.

　　Dr. KRAMER: There are number of regions that on MRI scans tend to show not just stability, but increases as a function of exercise in middle-age and older brains.

　　TRUDEAU: And these scientists are walking the walk. For all you baby boomers out there with middle-aged brains, heres what Dr. Kramer, age 56 and next, Dr. Small, age 58, do to keep their own brains healthy.

　　Dr. KRAMER: Before this interview, I was over at the gym, and I was riding a stationary bike and reading a few newspapers. And I was also lifting weights.

　　Dr. SMALL: And I'll start out in the New York Times, and I'll do "KenKen." And then either Ill solve it, or I get to the point where I screwed it up. And then I move on to the crossword. That's my typical day.

　　For NPR News, I'm Michelle Trudeau.