Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by different motor symptoms, including tremor, which is particularly difficult to manage. Common treatments, such as dopaminergic therapy, can have limitations in efficacy. Recent advancements in non-invasive brain stimulation, specifically phase-adaptive transcranial alternating current stimulation (tACS), offer a promising approach to reduce PD tremor. In the current project, a newly developed closed-loop system delivers precisely synchronized cerebellar tACS by aligning stimulation with the intrinsic hand tremor signal. The study will assess the efficacy of this novel approach to reduce hand tremor in PD patients.