Core I performs a comprehensive clinical assessment of all subjects (controls and PD patients) to be studied in Projects II and III. Subjects are comprehensively assessed with well-established clinical, motor, and neuropsychological instruments. We use the recently published consensus neuropsychological measures recently published by PANUC and the University of Pennsylvania Udall Center to facilitate our growing interactions with these Centers. This core also performs vesicular monoaminergic transporter type-2 (VMAT2) positron emission tomography (PET) using 11C-DTBZ brain and magnetic resonance (MR) imaging.