Title: Investigating the effects of galvanic vestibular stimulation on dynamic balance control in Parkinson’s disease
Supervisor: Dr. Mark Carpenter
Committee members: Dr. Tim Inglis, Dr. Romeo Chua
Abstract: Parkinson’s disease (PD) is a neurodegenerative disease characterized by tremor, bradykinesia, rigidity, and postural instability. As postural instability worsens with disease progression, this can result in falls, leading to loss of independence and quality of life. Previous research on PD has attributed dynamic balance deficits to ineffective sensory integration, abnormal generation of motor patterns, and excessive background muscle tone, however further research is needed to investigate the dynamic characteristics of responses to balance perturbations. Furthermore, a common treatment method in PD is a dopaminergic medication that shows mixed effects on balance control. Recently, using galvanic vestibular stimulation (GVS) as a non-invasive treatment method for PD has shown some benefits in postural stability, gait, and motor control. However, the majority of research on GVS and postural stability in PD has focused on static balance, and there has been little research using dynamic posturography. Therefore, the proposed research has two main goals: (1) characterize dynamic balance responses in PD during transient and continuous support-surface tilt perturbations and (2) examine the effect of subthreshold GVS on these dynamic perturbation responses.
PD patients (proposed n=15) in their best clinical “ON”-medication state and healthy controls (proposed n=15) will complete one visit. GVS subthreshold stimulation and sham-stimulation (0mA) trials will be used to control for placebo effects and participants will be blinded to the type of stimulation. In the anteroposterior (AP) direction on a tilting platform, participants will complete: (1) a series of transient perturbations at both 3° and 6° amplitudes, (2) a series of continuous perturbations with (a) eyes open (EO), (b) eyes closed (EC), (c) EO-EC, where participants will start with EO then are instructed to close their eyes randomly (by an auditory signal), and (d) EC-EO (vice versa), and (3) maximal voluntary contractions (MVCs), recorded from several muscles of the leg using surface electromyography (EMG). EMG activity during the perturbations and MVCs will be used to calculate onset latencies and amplitudes. Kinematic data from perturbation trials will be recorded from the head, hip, and ankle to calculate average displacement, AP inclination, and center of mass (COM) sway. Force plate data from perturbation trials will be used to calculate AP ankle torque.
Based on previous work, it is hypothesized that PD patients will exhibit abnormal balance across both types of perturbations. This will be characterized by larger and inappropriately scaled reflex amplitudes, excess co-contraction, and decreased AP ankle torque changes during transient perturbations. During continuous perturbations, this will be characterized by greater sway and a delayed implementation of new postural strategies when changing visual reference. Additionally, it is hypothesized in PD patients that subthreshold GVS will improve AP ankle torque changes during transient perturbations, and during continuous perturbations, will improve COM sway and the implementation of postural strategies when changing visual reference.