A wealth of evidence suggests that happiness is mediated by an area of the brain known as the left pre-frontal cortex. The frontal cortex takes up about half of the entire cortex, which is the outer covering of the brain. The prefrontal cortex is the most anterior (or forward) part of the frontal cortex (see Chapter 3 for more on brain anatomy). Brain imaging studies, electro-encephalogram (EEG) studies, and even research on the effect of strokes all support the role of the left prefrontal cortex in positive emotions.

Richard Davidson has conducted a number of investigations in this area. In one 2003 study conducted with John Cabott Zinn and a group of other colleagues, 25 subjects trained in meditation techniques were compared to a control group who had been put on a wait list. Meditation has been shown to have a strong impact on positive mood. Study subjects who completed the eight-week course in meditation showed a much greater increase in electrical activity in the left frontal regions than did wait-listed controls. Moreover, this group also showed a better immune response to a flu vaccine they received after their meditation course.