This project studies the impulsive side effects of common treatments for Parkinson's Disease. By learning how parts of the brain involved in Parkinson's encode information related to reward and motivation, the investigators will better understand the reasons why Parkinson's patients often suffer from compulsive gambling, hypersexuality, and repetitive tinkering ("punding"). These results may lead to the design of better methods of deep brain stimulation (DBS) that minimize the behavioral side effects of Parkinson's treatment.