​​​Individualising Noisy Galvanic Vestibular Stimulation for Postural Control in Bilateral Vestibulopathy​​

​​​Bilateral vestibulopathy (BVP) is characterised by bilaterally reduced vestibular function, resulting in gait instability, oscillopsia, and reduced quality of life.​​ ​Noisy galvanic vestibular stimulation (​​​​​​​nGVS​​​​​​​) is a promising modality to augment vestibular afferent input and improve postural control, yet clinical translation is constrained by uncertainty regarding optimal stimulation parameters, reliance on optimisation methods that may not reflect the functional limitation of individuals with BVP, and variability in individual responsiveness.​

The objectives of this thesis were to a) Critically appraise the nGVS literature to identify how stimulation parameters, task, context, and methodological factors shape reported responses. b) Develop a theoretically grounded optimisation framework for nGVS and c) Test the feasibility of the proposed optimisation framework, investigating whether a gait‑based protocol can be used to optimise nGVS parameters in people with BVP. ​These objectives were addressed through a series of studies including: a systematic review and meta-analysis of the efficacy of nGVS in BVP, a scoping review of nGVS parameters, a perspectives paper exploring the theoretical constructs of nGVS optimisation, a pilot matched-group observational study examining the spatiotemporal characteristics of gait in individuals with BVP, and a feasibility study using an experimental repeated-measures design to investigate gait as a means of optimisation.​

The review findings suggest nGVS can produce moderate improvements in postural control in people with BVP. However, considerable heterogeneity across studies in noise waveform, amplitude, frequency band, optimisation method, electrode features, and the electrode-skin interface made comparing findings and determining optimal parameters difficult.

A gait-based optimisation framework for nGVS in people with BVP is a feasible means of identifying individualised stimulation settings associated with changes in stability and variability during gait. ​Responses to nGVS were not uniform across participants and effects did not conform to a single or consistent stochastic resonance pattern.​ Instead, nGVS appeared to influence postural control in ways that were highly task-specific, context-dependent, and individually variable. Group-level averages may obscure individual responses, and a personalised approach is likely necessary for the translation of nGVS into clinical practice.This thesis advances the field in four principal ways. First, it demonstrates that nGVS has a moderate effect on postural control in BVP, although its effects appear to be shaped by task, context, and signal parameters. Second, it identifies the nGVS parameters most likely to affect neuromodulatory efficacy and provides reporting recommendations to support more rigorous and transparent research practices. Third, it clarifies the biomechanical nature of gait impairment in BVP by distinguishing instability and variability from relatively preserved aspects of pace and rhythm, thereby identifying functionally relevant targets for optimisation. Fourth, it establishes the feasibility of a functionally grounded framework for individualising nGVS using gait-based measures. Together, these findings move the field beyond the question of whether nGVS works towards a more precise understanding of how it may be personalised and applied in rehabilitation. Although considerable work remains to establish reproducible protocols, determine clinical meaningfulness, and identify who is most likely to benefit, this thesis provides a foundation for future work aimed at developing task-specific, clinically meaningful, vestibular neuromodulation.