Pain in Parkinson's Disease: Exploration of the Serotonin System in Positron Emission Tomography (PET [18F]-MPPF)

This study is investigating whether changes in the brain's serotonin system (a chemical messenger) might explain why some Parkinson's disease patients experience chronic pain. Researchers will use a special type of brain scan (PET scan) to compare brain activity in Parkinson's patients with and without pain. **You may be eligible if...** - You have a confirmed diagnosis of Parkinson's disease - You have been on a stable Parkinson's medication regimen for at least 4 weeks - You score above 25 on a standard memory and thinking test (MoCA) - You have mild-to-moderate depression (HADS-D score ≥11) - If enrolling in the "pain" group: you have chronic central pain related to Parkinson's for at least 3 months, rated at least 4/10 in severity - If enrolling in the "no pain" group: your pain is 4/10 or less and does not interfere with daily life **You may NOT be eligible if...** - You are receiving second-line Parkinson's therapy - You have a significant psychiatric history - You take medications that interact with serotonin receptors (5HT1A) - You have a contraindication to MRI (e.g., metal implants) - You have severe involuntary movements (dyskinesias) that would interfere with the scan Talk to your doctor to see if this trial is right for you.