1. Parkinson's Participants Only: A neurological examination will be performed by administering several clinical scaled. These clinical scales include the Unified Parkinson's Disease Rating Scale (UPDRS), the self-report Parkinson's Disease Quality of life scale (PDQ-39), MMSE instrument for cognitive (or memory) testing, and Beck Depression Inventory (BDI II) for evaluation of mood and depressive symptoms. The PDQ-39, MMSE, and BDI will each only be administered once and therefore will not be repeated at every study visit.