Neuroplasticity and multisensory training invirtual reality: a multimodal MRI investigationacross healthy and hemianopic populations

Abstract

This thesis investigates behavioural, structural, and functional plasticity induced byvisuomotor and audiovisual (AV) training in healthy adults and stroke survivors withhomonymous hemianopia (HH). A multimodal neuroimaging framework was applied,combining Diffusion Kurtosis Imaging (DKI), Diffusion Tensor Imaging (DTI), task-basedfunctional MRI (fMRI), and functional connectivity (FC) analyses to characterise training-related brain adaptation.In healthy adults, 6 weeks of voluntary eye-movement training produced reliablemicrostructural changes. DKI revealed significant reductions in kurtosis and diffusivitywithin early visual cortices, particularly the cuneus, with greater sensitivity than DTI inregions such as the pericalcarine cortex. Systematic differences in Bland–Altman analysisconfirmed training-related effects localised to the trained visual field. Using the same cohort,task-based FC analyses showed strengthened coupling between the frontal eye field (FEF)and posterior occipital cortex, and between the cuneus and cerebellum. These increasesscaled with individual improvements in reaction time, demonstrating taskspecific networkreorganisation aligned with behavioural learning.In stroke survivors with HH, 6 weeks of immersive VR-based AV training yielded significantbehavioural improvements across trained and untrained tasks. DTI indicated plasticity inpreserved occipital, thalamic, and temporal regions, reflected in increases in fractionalanisotropy (FA) and reductions in axial diffusivity (AD). FC analyses identified strengthenedconnectivity between medial visual cortex and occipital and auditory regions, with structuraland functional changes overlapping spatially, suggesting convergent compensatorymechanisms. Exploratory fMRI contrasts revealed spatially restricted activation changesconsistent with practice-related efficiency rather than large-scale restoration of damagedpathways. Lesion volume was negatively associated with responsiveness across behaviouraland imaging measures.Together, these studies demonstrate that both visuomotor and AV training induce rapidstructural and functional plasticity, with early visual cortices and the cerebellum emerging asshared hubs of adaptation. In HH, additional recruitment of multisensory pathways reflectscompensatory reorganisation of spared networks. These findings highlight the potential ofimmersive VR and multisensory methods for enhancing neurorehabilitation in chronic visualfield loss.