Use it or lose it. We know that about our bodies.
But a growing line of research now shows that the same is true for our brains. How we live, and what we do, can actually have a profound impact on the physical structure of the brain.
If we are what we eat, as the old saying goes, we may also be what we think. Or how we think, as well as how much we think.
One treatment for some of our mental ills may well lie in the practice of meditation, an awareness of sensations, feelings and state of mind.
The latest evidence comes from an impressive group of researchers from some of the leading institutions in the world who have found that a serious effort at meditation can physically change the brain, leading to reduced stress, better mental focus, and possibly fewer effects from aging.
"The structure of the brain is very complex and it is constantly changing," says Sara Lazar, a psychiatrist and research scientist at Massachusetts General Hospital and Harvard University. "It is well documented that around the age of 20 to 25 the whole front of the brain starts to get thinner with age, and other parts of the brain continue to grow, and all sorts of things are happening, all of the time."
Diet, education, aging and how we use our time all have a big impact on changes in the structure of the brain, she notes.
Lazar, who is obsessed with how the human brain functions, took up meditation nearly a decade ago, partly because she had heard reports of how it can help keep the brain in tune, but she wasn't sure if it was true.
Today, she has very little doubt.
"The difference is like night and day," she says. It shows up in a reduction in stress, being able to remain focused and dealing with "difficult situations," she says.
And now, she has reason to believe it changed her brain physically, in ways that are consistent with improvement in all those areas.
Lazar led a team of researchers who used that fantastic new tool, magnetic resonance imaging, to literally peer into the brains of 20 subjects who regularly practice meditation, and 15 who don't. They found that the regions of the brain that are associated with attention, sensory processing and stimulation where "thicker" in the brains of the meditators than in the others. The evidence also suggests that meditation may help ward off the thinning of those regions of the brain caused by aging.
What's interesting about the study is these meditators aren't a bunch of monks. Previous research had already shown that Buddhist monks in Tibet who were devoted to meditation and spent many hours every day practicing it had experienced changes in mental processing.
But Lazar and her colleagues wanted to know if this only worked for those who are totally immersed in the process, or if a few hours a week do the same thing.
Participants in the study meditated only an average of about 40 minutes a day. Some had done it for only a year or so. Others had done it for decades.
The structural changes were most prominent among those who have meditated for longer periods, and it was especially strong for those who showed evidence of having mastered the art.
The participants in the study were "people who practice mindfulness-based meditation, paying attention to breathing and internal processes," says Jeremy Gray, a cognitive psychologist at Yale and a co-author of the study, which appeared in a November issue of NeuroReport.
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.