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Abstract

Impaired motor vigour (MV) is closely associated with bradykinesia, a cardinal motor symptom of Parkinson’s disease (PD), and has been primarily characterized through discrete movements. It remains unclear whether MV deficit also underlies motor impairments in rhythmic contexts, such as the bradykinetic balance control during locomotion. The sequence effect (SE), defined as the progressive decline in movement amplitude and speed over repetitions, is another proposed manifestation of diminished MV. Galvanic vestibular stimulation (GVS) has shown promise for improving MV; however, its efficacy is hampered by considerable variability in individual responsiveness. Moreover, the effects of GVS on the SE and on dynamic balance control during gait in PD have not been systematically investigated. This thesis implemented a precision-designed GVS protocol for each participant based on improvements in MV. Seventeen participants with PD performed finger-tapping and walking tasks under personalized optimal and sham GVS conditions delivered via a wireless stimulator while in the ON medication state. Finger-tapping kinematics were extracted from video recordings, and tri-axial trunk sway amplitudes during walking were analyzed using ten wearable sensors to indicate dynamic balance. Compared with the sham condition, optimal GVS increased tapping amplitude and velocity on the more affected side, in addition to shortening inter-tap intervals. However, variability and SE, modeled as the slope of parameter decrements over the sequence, were not significantly affected by optimal GVS. During walking, trunk frontal range of motion (ROM) was reduced by optimal GVS across walking speeds, thereby conserving trunk frontal dynamics during locomotion. The absence of sagittal ROM changes, along with speed-dependent modulation of GVS effects on trunk frontal and horizontal ROMs, confirms that vestibular contributions to motor control are selective and dynamically modulated according to movement state. Overall, this thesis supports the use of personalized GVS protocols as a complementary therapy to current pharmacological treatments for PD. Findings from two rhythmic motor tasks highlight the central role of impaired MV in diverse motor deficits and establish a framework for precision neuromodulation to target MV as the fundamental aspect of PD pathophysiology.