A Randomized Double-Blind Active-Controlled Crossover Trial of Respiratory-Gated Versus Non-Gated Transcutaneous Auricular Vagus Nerve Stimulation for the Treatment of Motor and 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 motor and 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 motor or 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.