Temporal Interference Stimulation on Motor Symptoms in Parkinson's Disease

The goal of this clinical trial is to learn whether a type of brain stimulation called transcranial temporal interference stimulation (TIS) of the internal globus pallidus (GPi) can help improve movement symptoms in people with Parkinson's disease. The study will also look at how TIS changes brain activity related to these improvements. The main questions this study aims to answer are: * How much can repeated TIS sessions improve movement symptoms in people with Parkinson's disease? * Can these improvements last for up to two months after the treatment ends? * What changes in brain activity happen along with the improvements? Researchers will compare people who receive active TIS with those who receive sham (placebo-like) stimulation to see whether active TIS leads to better movement outcomes. Participants will: * Receive 10 sessions of active or sham TIS over two weeks * Complete movement assessments during the two-week treatment and again 2, 4, and 8 weeks afterward * Complete brain activity assessments before and after the two-week treatment