Thanks to the Dalai Lama, lots of monks have lent Richard Davidson their brains. For almost 20 years Davidson, a neuropsychologist at the University of Wisconsin, Madison, and a long-time meditator himself, has been curious about how Buddhist meditation of the kind the monks practice might change their brains. He has lugged electronic equipment up into the hills above Dharamsala (the Dalai Lama's home in exile in northern India) to test the brains of yogis, lamas and monks living in primitive huts there, and persuaded other monks to visit his lab.

Over the years he has found that the brains of monks who are the most experienced meditators are indeed different from other brains. They have a much stronger "gamma" wave, a form of electrical activity in the brain that is associated with consciousness and pulling together information and perceptions from different regions of the brain. They also have much greater activity in the left than the right prefrontal cortex (just behind the forehead), a mark of well-being and happiness.

But all of these studies came with an asterisk. There was no way to tell if the monks' brains started out different. That is, maybe people with high gamma-wave activity and lopsided left-prefrontal activity were more likely to become Buddhist monks. If so, then their brain traits caused them to become expert meditators, rather than their years of meditation changing their brain.

Now Davidson has taken a big step toward showing that the causal arrow really does point from meditation to brain changes rather than from brain differences to a life of meditation. Specifically, meditation can change brain circuits linked to attention.

The old dogma that the adult human brain cannot generate new neurons was overthrown almost 10 years ago, but a question persists: do those new neurons do any good?

In 1998 scientists led by Fred (Rusty) Gage of the Salk Institute for Biological Sciences discovered that older adults "well into their 50s, 60s and even 70s "continue to produce new neurons in their brains. Last November, a study found that as little as three hours a week of brisk walking increases blood flow to the brain and increases production of new neurons, researchers reported in the Journal of Gerontology: Medical Sciences. The same team, led by Arthur Kramer of the University of Illinois, had earlier shown that older adults who engage in physical activity have better working memory, are more adept at switching between mental tasks (a skill that generally declines with age), and are better able to screen out distractions (ditto) compared to people of the same age who did not get exercise training. The obvious question arose: is the reason exercise improves cognitive function in older adults that it boosts "neurogenesis," the production of new brain neurons?