From an article in the New York Times titled Is Buddhism Good for Your Health?:

“In Buddhist tradition,” Davidson explains, “‘meditation’ is a word that is equivalent to a word like ‘sports’ in the U.S. It’s a family of activity, not a single thing.” Each of these meditative practices calls on different mental skills, according to Buddhist practitioners. The Wisconsin researchers, for example, are focusing on three common forms of Buddhist meditation. “One is focused attention, where they specifically train themselves to focus on a single object for long periods of time,” Davidson says. “The second area is where they voluntarily cultivate compassion. It’s something they do every day, and they have special exercises where they envision negative events, something that causes anger or irritability, and then transform it and infuse it with an antidote, which is compassion. They say they are able to do it just like that,” he says, snapping his fingers. “The third is called ‘open presence.’ It is a state of being acutely aware of whatever thought, emotion or sensation is present, without reacting to it. They describe it as pure awareness.”

The fact that the brain can learn, adapt and molecularly resculpture itself on the basis of experience and training suggests that meditation may leave a biological residue in the brain — a residue that, with the increasing sophistication of new technology, might be captured and measured. “This fits into the whole neuroscience literature of expertise,” says Stephen Kosslyn, a Harvard neuroscientist, “where taxi drivers are studied for their spatial memory and concert musicians are studied for their sense of pitch. If you do something, anything, even play Ping-Pong, for 20 years, eight hours a day, there’s going to be something in your brain that’s different from someone who didn’t do that. It’s just got to be.”