Neuroscientists from Massachusetts General Hospital report that meditation actually increases the thickness of the brain’s cortex, specifically regions associated with attention and the processing of sensory information. They conducted MRI brain scans on 15 meditators of varying experience and 15 non-meditators. From New Scientist:

“You are exercising (the cortex) while you meditate, and it gets bigger,” (researcher Sara Lazar) says. The finding is in line with studies showing that accomplished musicians, athletes and linguists all have thickening in relevant areas of the cortex. It is further evidence, says Lazar, that yogis “aren’t just sitting there doing nothing”.