Toosy, Ahmed Tahir; (2005) Damage and recovery of visual and motor central nervous system pathways investigated with structural and functional magnetic resonance imaging. Doctoral thesis , UCL (University College London).

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Abstract

The investigations in this thesis applied magnetic resonance imaging (MRI) techniques to study structural and functional aspects of central nervous system (CNS) damage and recovery. The principal disease model investigated was optic neuritis (ON) for the visual system. A longitudinal study of acute optic neuritis was performed, in which patients were studied over one year. Functional and optic nerve structural MRI were performed, along with detailed clinical assessments. Analysis of the functional MRI (fMRI) data revealed differential deactivation behaviours outside the occipital cortex in ON patients when compared with healthy controls. Further correlation analyses, in which fMRI and optic nerve structure data were combined, presented evidence for adaptive cortical plasticity in higher visual processing areas early after optic neuritis onset. Diffusion tensor imaging (DTI) was then introduced as a potentially valuable technique for investigating white matter structure. It was applied to the corticospinal pathways of amyotrophic lateral sclerosis patients, which showed reduced fractional anisotropy (FA), a measure of white matter structural integrity, when compared with healthy controls. DTI tractography, an exciting development of DTI, was subsequently used to develop probabilistic mapping of white matter tracts (including visual and motor pathways) for multiple subjects. This methodology was applied to a group of subjects who also underwent fMRI scanning for the visual system. The integration of DTI tractography and fMRI derived information discovered a function-structure gradient within the posterior visual pathways: the visual cortex fMRI response correlated with the FA of the probabilistically segmented optic radiations. Finally, a preliminary study of ON patients applied this novel methodology to investigate their posterior visual function-structure gradients and found differences, compared with controls.

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