Testing of an Interface for Synchronizing tACS-DBS With a Phase-locked-loop

This study is testing whether a brain stimulation technique called transcranial alternating current stimulation (tACS) can be synchronized with a deep brain stimulator (DBS) device in people who already have a DBS implant for Parkinson's disease. The goal is to assess the safety and feasibility of combining these two brain stimulation approaches. **You may be eligible if...** - You already have a deep brain stimulator (DBS) implanted for Parkinson's disease or another approved condition - Your DBS device is compatible with the study's synchronization interface - You are in stable health and able to attend study sessions **You may NOT be eligible if...** - You have a DBS device that is incompatible with external stimulation - You have a history of seizures - You have metal implants in your head besides the DBS that could interact with tACS - You are pregnant Talk to your doctor to see if this trial is right for you.