So you fell asleep easily enough, but now it's 3 a.m. and your mind is spinning and rest is elusive. You're reliving every foolish or embarrassing thing you did in the past 24 or 48 or 72 hours, and that is a lot of material to run through. And you simply can't stop.

Except maybe you could, if only you knew how to be mindful.

“When you're caught in that loop of rumination, that's very real, and it creates very intense feelings,” said psychologist and journalist Daniel Goleman, who reported on brain and behavioral sciences for a New York newspaper. “If you're mindful, you realize it's just a thought. You don't have to believe your thoughts. You can question them, and that changes them. It takes energy from the brain that creates the heaviness. Looking at it in a different way makes the rumination less intense.”

You might think, on hearing such praises of mindfulness — a form of meditative practice — that it will solve just about every problem in your life. Meditation can halt the late-night rumination cycle, right?

So can't it also make you into a better person? Enlarge your brain? Make you taller and thinner and richer? Well, no, said Goleman, who's also the author of the best-selling book “Emotional Intelligence.” Some claims of meditation's power are overblown. Some studies are less rigorous than they should be. But science has proven that meditation can induce healthy and important physical improvements, such as lowering your blood pressure, decreasing relapses into depression and managing chronic pain.

As our interest in meditation grows, how do we know what's too good to be true?

Goleman and Richard J. Davidson, who directs a brain lab and founded the Center for Healthy Minds at the University of Wisconsin-Madison, have just published “Altered Traits: Science Reveals How Meditation Changes Your Mind, Brain, and Body.” The book separates truth from fiction, debunking studies and highlighting meditation's startling effects on the brain.

“Altered Traits” also chronicles the authors' decades-long friendship and lifelong interest in the subject of meditation, which began at a time when scientific circles had little patience or interest in the subject.

“Altered Traits” examines scientific studies on meditation and the benefits of intensive retreats, learning to view our selves and our brains in a whole new light and the importance of a good teacher (“I feel strongly the quality of the teacher is important,” Goleman says).