A Massachusetts General Hospital study in next week's Psychiatry Research: Neuroimaging shows marked brain changes over an eight-week practice of mindfulness meditation. Of course, by definition, every experience you have makes changes in your brain (that's pretty much the definition of experience: "something that changes your brain"), but in this case, the changes point to deep and lasting effects as a result of meditation that correspond to the reported experience of meditators. (This confirms earlier research from the hospital, like this study from 2005).
Meditation group participants reported spending an average of 27 minutes each day practicing mindfulness exercises, and their responses to a mindfulness questionnaire indicated significant improvements compared with pre-participation responses. The analysis of MR images, which focused on areas where meditation-associated differences were seen in earlier studies, found increased grey-matter density in the hippocampus, known to be important for learning and memory, and in structures associated with self-awareness, compassion and introspection. Participant-reported reductions in stress also were correlated with decreased grey-matter density in the amygdala, which is known to play an important role in anxiety and stress. Although no change was seen in a self-awareness-associated structure called the insula, which had been identified in earlier studies, the authors suggest that longer-term meditation practice might be needed to produce changes in that area. None of these changes were seen in the control group, indicating that they had not resulted merely from the passage of time.