The "other" side of Dopamine

"While dopamine neurons are relatively rare, they are clustered in very specific areas in the center of the brain, such as the nucleus accumbens and ventral striatum. These cortical parts make up the dopamine reward pathway, the neural system that’s responsible for generating the pleasurable emotions triggered by pleasurable things.  It doesn’t matter if we’re having sex or eating sugar or snorting amphetamine: These things fill us with bliss because they tickle these cells.

But the caricature of dopamine as simply the chemical of hedonism is woefully incomplete. For instance, studies have shown that the dopamine reward pathway is also extremely active when people are forced to eat something disgusting, or when a subject is gasping for air after holding their breath. These are intensely unpleasant experiences, and yet our dopamine neurons are pumping out neurotransmitter. This leaves two possibilities: 1) We are all secret masochists, and take pleasure in pain or 2) Dopamine is really about attention and motivation, and is not just the chemical of pleasure and rewards."

-more here