One clear measure of how deeply the participants slipped into meditation was changes in their breathing rates.
"How much it slowed down showed their degree of expertise while engaged in meditation," Gray says.
Those whose breathing slowed the most, and thus were more deeply involved in meditation, were the ones who showed the greatest changes in their brain structure.
Lazar says that "strongly suggests" the difference in the brain structure was caused by meditation, and not the other way around -- that differences in their brains is what got them into meditation in the first place.
The findings are consistent with other research showing that physical activity can also change the brain.
There have been some studies, for example, showing that people who engage in such things as juggling change more than their dexterity. They also change their brains.
"People learned how to juggle three balls, and after doing that for a couple of months the brain structure in regions that are related to visual attention was thickened," says Gray. "After they stopped juggling the thickness started to decrease again."
The new research shows a similar result from meditation.
The findings were enough to convince Gray to take a crack at it. And he admits it wasn't easy.
"It's very difficult to not do anything," he says. "We're so primed to do things that we're always leaping up to do things. It's hard to just completely chill."
But after trying it a few times, he began to get the hang of it.
"Its very different from day dreaming, and it's different from sleeping," Gray says. "It's very active, but very calm and focused. In day dreaming you're not paying attention at all. You're being carried along by the stream of your thoughts rather than noticing them and observing them and reflecting upon them."
There are, of course, many forms of meditation. Whether all forms have the same affect is unknown, but the researches suspect that other types of mental discipline, like yoga, could also alter the physical structure of the brain. But so far it looks like if you want to get the benefits, you've got to do the work.
"We suspect it's going to be a lot like physical exercise," Lazar says. "If you go to the gym once a week, versus every day, it gives you some benefits, but going every day is going to give you a lot more.
"These are people [the study participants] who go to the 'gym' every day, but we suspect that people who do less than that will still receive benefits," she says.