Parkinson’s results from the loss of cells in the brain that produce a neurotransmitter known as dopamine. The treatment for Parkinson’s is to increase the patients’ dopamine levels—usually by increasing the body’s production of the chemical, and sometimes by using medications that directly bind to dopamine receptors. But it turns out that dopamine is a chemical on double duty in the brain. Along with its role in motor commands, it also serves as the main messenger in the reward systems, guiding a person toward food, drink, mates, and all things useful for survival. Because of its role in the reward system, imbalances in dopamine can trigger gambling, overeating, and drug addiction—behaviors that result from a reward system gone awry