This ability to change the brain's wiring, to grow new neural connections, has been demonstrated in experiments such as one conducted by Doctors Avi Karni and Leslie Underleider at the National Institutes of Mental Health. In that experiment, the researchers had subjects perform a simple motor task, a finger-tapping exercise, and identified the parts of the brain involved in the task by taking a MRI brain scan. The subjects then practiced the finger exercise daily for four weeks, gradually becoming more efficient and quicker at it. At the end of the four-week period, the brain scan was repeated and showed that the area of the brain involved in the task had expanded; this indicated that the regular practice and repetition of the task had recruited new nerve cells and changed the neural connections that had originally been involved in the task. This remarkable feature of the brain appears to be the physiological basis for the possibility of transforming our minds. By mobilizing our thoughts and practicing new ways of thinking, we can reshape our nerve cells and change the way our brains work. It is also the basis for the idea that inner transformation begins with learning (new input) and involves the discipline of gradually replacing our "negative conditioning" (corresponding with our present characteristic nerve cell activation patterns) with "positive conditioning" (forming new neural circuits). Thus, the idea of training the mind for happiness becomes a very real possibility.

— Dalai Lama

from The Art of Happiness