The Electrophysiological Effects of Vestibular Stimulation in Parkinson's Disease

A recent study showed that vestibular stimulation can produce long-lasting alleviation of motor and non-motor features in Parkinson’s disease (PD). The improvements observed in motor symptoms were of particular note and may provide an indication as to one of the underlying physiological mechanisms of action for vestibular stimulation. An electrophysiological marker known to be abnormal in PD is the Bereitschaftpotential (BP) of the movement-related cortical potentials (MRCPs). One aim of this thesis was to observe the effects of galvanic vestibular stimulation (GVS) on MRCPs in PD to better understand its underlying physiological mechanisms. Many studies measuring the electrophysiological response to GVS have employed pre- versus post-GVS protocols, limiting observations to only after stimulation. The investigation of the mechanisms during GVS is limited by the large artifacts that contaminate the electroencephalograph (EEG). Previous studies have described pre-processing strategies to remove the GVS-related artifact, but these have many limitations. Thus, another aim of this thesis was to describe an artifact removal strategy using a novel approach of employing Independent Components Analysis (ICA) to identify, quantify and eliminate the GVS-related artifact from the EEG data. Study 1 (n = 11) validated this strategy by successfully removing the GVS-related

artifact from MRCP data when manipulating the GVS frequency. Study 2 (n = 9) provided further validation by showing successful removal of the GVS-related artifact associated with a higher GVS intensity. Study 3 applied the methodology validated in the first two studies to a PD sample and found a significant increase in the early BP associated with GVS. This suggests that vestibular stimulation may improve motor features in PD through modulation of underlying pathological oscillations associated with motor dysfunction.