Wired 14.02: Buddha on the Brain is a really interesting Wired story I just read about observations of Tibetan monks who have changed to physiology of their brain structure through meditation.
Apparantly, Tibetan mocks showed massive, positive differences in their brain activity, compared with a control group of non meditators:

• “… The monks produced gamma waves that were 30 times as strong as the students’. In addition, larger areas of the meditators’ brains were active, particularly in the left prefrontal cortex, the part of the brain responsible for positive emotions…”

I can personally attest to the relaxing affects of yoga, the most effective stress reliever ever.
The most gratifying thing about this is that you _can_ train your brain through activity…I better crackout those Soduko books.