Cortical plasticity and recovery of visual function following optic radiation stroke

Using a modification of an existing method of probabilistic magnetic resonance tractography analysis, optic radiation images were automatically generated in young healthy subjects, which closely matched histological reference data. Optic radiation loss defined in native space in stroke patients correlated with severity of visual field loss; the strength of the correlation was reduced by visual field recovery, perhaps suggesting underlying brain plasticity. Using a rapid psychophysical method of contrast sensitivity measurement, validated in this study against a criterion-free forced-choice method, contrast sensitivity loss in different regions of the visual field was measured. In the small sample of stroke patients, losses were found both at visual field defect borders, where recovery had likely occurred and, more surprisingly, in the central visual field which appeared never to have been involved in the visual field defect. Finally, using functional magnetic resonance imaging to map the retinotopic organization of the visual areas of the cerebral cortex in the same patients, preliminary evidence was obtained fro visual cortex plasticity, in the form of topographical reorganization in visual area V2 (Brodmann area 18), and in one illustrative patient topographical reorganization of the opposite hemisphere so that V1 contained a representative of the recovered region of visual field. Overall, the study suggests that vision recovers after stroke independent of physical recovery, and this may involve topographical changes in visual cortex. It provides insights into brain structure, function and visual perception following optic radiation stroke, and has generated several tools for further study in this field.EThOS - Electronic Theses Online ServiceGBUnited Kingdo