Respiratory-gated Transcutaneous Auricular Vagus Nerve Stimulation for Improving Apathy in Parkinson's Disease

Inclusion Criteria: 1. Meet the diagnostic criteria for idiopathic Parkinson's disease (based on the MDS Clinical Diagnostic Criteria for Parkinson's Disease (2015 version)). 2. Patients with Apathy Motivation Index (AMI) score \>1.7. 3. All PD patients must be on stable, standardized medication regimens with no adjustments to medications for at least 1 month prior to the study and throughout the study period. 4. Demonstrate good compliance and adherence, capable of completing behavioral tests and taVNS therapy. 5. Mini-Mental State Examination (MMSE) score ≥22. 6. Meet safety criteria for MRI screening. Exclusion Criteria: 1. Prior brain MRI/CT showing focal brain lesions or severe white matter disease (Fazekas grade 3 or higher). 2. Secondary parkinsonism (e.g., vascular parkinsonism, drug-induced parkinsonism). 3. History of severe traumatic brain injury, neurosurgery, or deep brain stimulation (DBS) therapy. 4. Personal history of epilepsy, unexplained loss of consciousness, or current use of anticonvulsant medications for seizure control. 5. Diagnosis of neuropsychiatric disorders other than Parkinson's disease. 6. Current use of non-steroidal anti-inflammatory drugs (NSAIDs) or Non-benzodiazepine GABA receptor agonist drug or anticholinergics or corticosteroids, or history of substance abuse or drug addiction. 7. Participation in any clinical trial within the past 3 months. 8. Severe systemic comorbidities (e.g., hepatic/renal failure, arrhythmias, organic heart disease). 9. Pregnant/lactating women or subjects (including males) planning pregnancy within 6 months. 10. Contraindications to taVNS, such as cardiac pacemakers, post-DBS surgery, or auricular pathologies (e.g., tympanic membrane perforation).