Using diffusion-weighted tractography to investigate dysfunction of the visual system

Holly Bridge

(Oxford)

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Date: May 16, 2014

Description:

The functional consequences of damage to, or dysfunction of, different parts of the visual pathway have been well characterized for many years. Possibly the most extreme dysfunction is the lack of eyes (anophthalmia) which prevents any stimulation of this pathway by light input. In this case, functional MRI indicates the use of the occipital cortex for processing of language, and other auditory stimuli. This raises the question of how this information gets to the occipital cortex; are there differences in the underlying anatomical connectivity or can existing pathways be used to carry different information? Here I’ll describe several approaches we have taken to try to understand the white matter connectivity in anophthalmia using diffusion tractography. Damage to the visual pathway can also be sustained later in life, either to the periphery or to the post-chiasmatic pathway (optic tract, lateral geniculate nucleus, optic radiation or visual cortex). When damage occurs in adulthood, any changes to white matter are likely to be the result of degeneration. Sensitive measures of white matter integrity can be used to illustrate patterns of degeneration in patient populations. However, it is also the case that in the presence of lesions, and where white matter tracts are relatively small (e.g. optic tract) measures derived from diffusion-weighted imaging can be misleading. In summary I will present an overview of the potential for employing diffusion tractography to understand plasticity and degeneration in the abnormal visual system, highlighting potential confounds that may arise in patient populations.




Created: Friday, May 23rd, 2014