The Bright Side of Anger

On the whole, brain scans shore up what we've known all along about our emotions: some are positive and some are negative. Happiness, for instance, is positive — when people are in good moods, they tend to show more activity in certain regions on the left side of the brain. Emotions like depression and anxiety are negative, and tend to heighten activity in brain regions on the right.
But what about anger: positive or negative?