Subject participation includes two 25-30 minute MRI scans. The subject will arrive in the "off" state (PD medications withheld for approximately 12 hours prior to the scan). Following the initial scan, the subject will receive 125% of his or her usual daily morning dose of PD medications which is calculated as levodopa dose equivalents (LDE) and is given as carbidopa-levodopa. The subject will then wait for an hour allowing for the medication to begin working. During this time the subject will complete cognitive assessments, questionnaires regarding the history and current state of PD, and motor assessments. The subject will then undergo a second MRI scan of approximately 25-30 minutes. The subject after completing the second MRI scan is free to leave. The entire study is approximately 2 and 1/2 hours long.