Kinematic and Neural Dynamics of Postural Instability in Parkinson's Disease

This study is examining the movement patterns and brain activity that contribute to balance and posture problems in veterans with Parkinson's disease. The goal is to better understand what causes falls and unsteadiness and to explore how deep brain stimulation (DBS) affects these problems. **You may be eligible if...** - You are a veteran with a clinical diagnosis of Parkinson's disease - Your disease is at Hoehn and Yahr stage 2 or 3 (moderate, but you are still physically independent) - You are able to give informed consent (capacity assessed using a brief standardized tool) - For a sub-study: you also have a specific DBS device (STN DBS with a Percept unit) implanted **You may NOT be eligible if...** - You have dementia that significantly affects your ability to make healthcare decisions - You have another form of parkinsonism (such as PSP or CBGD) — not standard Parkinson's disease - Your disease is past stage 3 (you need assistance walking) - You have symptomatic low blood pressure when standing Talk to your doctor to see if this trial is right for you.