Inclusion Criteria:
* Diagnosis of idiopathic Parkinson's disease,
* On stable medication for the preceding month and anticipated over the next 3 months,
* Able to ambulate without the use of an assistive device for more than 50 meters.
Control Cohort:
* Age (± 3 years) and sex distribution matched to the PD cohort,
* Able to ambulate without the use of an assistive device for more than 50 meters.
Exclusion Criteria:
* Failure to demonstrate capacity to consent (based on UBACC and/or MacArthur-CR),
* History of significant neurological disorder (besides PD in the PD group),
* History of stroke, traumatic brain injury, intracranial aneurysm, intracranial hemorrhage, brain tumor or atypical parkinsonian disorder,
* Severe orthopedic or other related musculoskeletal pathology that has significant adverse effects on gait,
* Women who are pregnant or may be pregnant,
* Insufficient comprehension of the English language,
* History of substance abuse in past 2 years;
Additional exclusion criteria for VNS experiment
* Pain at the nVNS treatment site (e.g., dysesthesia, neuralgia, cervicalgia);
* Lesion (including lymphadenopathy), previous surgery (including carotid endarterectomy or vascular neck surgery) or abnormal anatomy at the stimulation site (open wound, rash, infection, swelling, cut, sore, drug patch, surgical scar\[s\]);
* Known or suspected severe atherosclerotic cardiovascular disease, severe carotid artery disease (e.g., bruits or history of TIA or stroke), congestive heart failure, known severe coronary artery disease or prior myocardial infarction;
* Abnormal baseline electrocardiogram (ECG) within the last year (e.g., second or third-degree heart block, prolonged QT interval, atrial fibrillation, atrial flutter, history of ventricular tachycardia or ventricular fibrillation);
* Recent history of uncontrolled high blood pressure, bradycardia, tachycardia, or know recent history orthostatic hypotension;
* Previous unilateral or bilateral vagotomy;
* Implanted metal cervical spine hardware, other metallic implants or implantable medical devices such as deep brain stimulator, hearing aid implant, pacemaker, implanted cardioverter defibrillator, cranial aneurysm and/or cranial aneurysm clips, history of facial/orbital/metallic fragments, implanted electronic device, neurostimulator, valve replacements/stents, metallic implants/prostheses) near the stimulation site such as a bone plate or bone screw;
* History of syncope or seizures (within the last 2 years);
