 - Participants with any form of drug-induced or atypical parkinsonism, cognitive impairment Mini-Mental State Examination MMSE score 23, a history of Diagnostic and Statistical Manual of Mental Disorders IV DSM IV diagnosed major depression, unstable mild depression or psychosis, or participants taking tolcapone will be excluded. Participants with mild depression who are well controlled on a stable dose of an antidepressant medication for at least 4 weeks before screening will be eligible. 