Properties of visual field maps in health and disease

• Main Author: Gouws, André D.
• Other Authors: Morland, Antony B. ; Green, Gary G. R.
• Published: University of York 2015
• Subjects: 150
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682326

The visual world that surrounds us is represented in and processed by multiple topographically organised maps in the human brain. The organising principle underlying these retinotopic maps is also apparent across other sensory modalities and appears highly conserved across species. Moreover, the template for these visual maps is laid down during development, without the need for visual experience. This thesis binds and summarises seven publications describing work to characterise the functional properties of visual maps in the human brain. Initially, we describe TMS and fMRI measurements designed to probe the functional specificity of two spatially distinct but spatially adjacent maps, LO-1 and LO-2. Concurrently I developed software (visualisation tools) for precise dissection of these areas and to more broadly facilitate the visualisation of neuroimaging data. Our experiment revealed a double dissociation in the functional specificity of these areas, with preferential processing of orientation and shape information by LO-1 and LO-2, respectively. We then used fMRI to examine the effect of spatial attention on the responses measured from visual field maps. We showed that attention modulated visual responses by both enhancing attended locations and suppressing unattended locations; these effects were evident in the maps of early visual cortex and subcortical structures including the lateral geniculate and pulvinar nuclei. Finally, we examined the properties of visual field maps in patients with retinal lesions. Although maps can be abnormally organised with certain congenital visual deficits, we asked whether normally developed maps were able to reorganise when input to them is lost later in life, specifically due to central retinal lesions. Our measurements showed no evidence of reorganisation in the maps of patients with macular degeneration: the extent of activity measured in these maps was both highly predictable based on individual retinal lesions and could be reliably simulated in normally sighted individuals.