Effect of taVNS of Brainstem Activation in Early and Late Parkinson's Disease Patients - an fMRI Study

This is a randomised, within-subject, double-blinded, placebo-controlled study to assess the fMRI correlates of central nervous system (CNS) response to taVNS in early vs late-stage Parkinsons disease (PD), at two different frequencies. Forty PD patients will be included: twenty patients with early-stage (Hoehn and Yahr stage (HY) 1-2) and twenty patients with late-stage (HY 3-4) PD. Each patient will undergo one stimulation session, where they will receive active taVNS at 100 Hz (taVNS100), taVNS at 25Hz (taVNS25) or will have positioned electrodes without stimulation (xVNS). The order of taVNS100, taVNS25 and xVNS will be randomized between subjects. The session will include (1) xVNS and taVNS; (2) MRI and fMRI and (3) heart rate and breathing rate monitoring. Clinical assessment with the Movement Disorder Society-Unified Parkinson's Disease Rating Scale will be done before the session.