A Comparative Open-Label Crossover Study of Respiratory-Gated Versus Non-Respiratory-Gated Transcutaneous Auricular Vagus Nerve Stimulation for the Treatment of Non-Motor Symptoms in Parkinson's Disease

The goal of this clinical trial is to compare the effects of different modes and frequencies of transcutaneous auricular vagus nerve stimulation (taVNS) on non-motor symptoms in people with Parkinson\'s disease. The main questions it aims to answer are: Which mode and frequency of taVNS is most effective in improving non-motor symptoms? Are there any side effects or safety concerns with different taVNS frequencies? Researchers will compare three types of taVNS: 25 Hz non-expiratory gated, 25 Hz expiratory gated, and 100 Hz expiratory gated stimulation. Participants will: Receive each type of taVNS in three 2-week cycles, with 2-month breaks between cycles Undergo neuropsychological assessments, imaging, eye-tracking, and biological sample collection before and after each cycle.