Act of Meditation.

How long do you have to meditate to see such results? Well, in the study, participants were told to meditate for 40 minutes a day, but the average ended up being 27 minutes a day. Several other studies suggest that you can see significant positive changes in just 15 to 20 minutes a day.

As for Lazar's own meditation practice, she says it's "highly variable. Some days 40 minutes. Some days five minutes. Some days, not at all. It's a lot like exercise. Exercising three times a week is great. But if all you can do is just a little bit every day, that's a good thing, too."

Turns out meditating can give you the brain of a 25-year-old. Too bad it can't also give you the body of one.