In between meditations, the gamma signal in the monks never died down. Even when they were not meditating, their brains were different from the novices' brains, marked by waves associated with perception, problem solving and consciousness. Moreover, the more hours of meditation training a monk had had, the stronger and more enduring the gamma signal.

It was something Prof. Davidson had been seeking since he trekked into the hills above Dharamsala to study lamas and monks: evidence that mental training can create an enduring brain trait.

"This positive state is a skill that can be trained," Prof. Davidson says. "Our findings clearly indicate that meditation can change the function of the brain in an enduring way."