Functional and anatomical properties of visual cortex in individuals with congenital loss of cone photoreceptor function and normally sighted controls

The aim of this thesis was to systemically assess reported cortical reorganisation in achromatopsia, a congenital loss of cone photoreceptor function, to inform the current development of vision restoration approaches. Both, functional and structural magnetic resonance imaging (MRI) were used to answer if and to what extend the brain undergoes changes when visual input is lost from birth.
First, visual cortical representations of rod and cone driven signals were examined in normally sighted participants to detail differences between these two retinal pathways. We showed that spatial summation properties of the rod pathway are expressed at a cortical level and highlighted that low light levels mainly affect primary visual cortex, while extra striate areas, likely related to their increased spatial pooling properties, still show robust responses.
Further, functional MRI showed no differences in cortical responses at central visual field representations between achromats and controls, while achromats that presented with reduced rod function are characterised by a more severe reduction in cortical responses. Notably, traces of remapping in form of an eccentricity shift cannot be ruled out for some participants,
Last, this thesis examined brain integrity in achromatopsia using surface-based morphometry and revealed that surface area is reduced across primary visual cortex. Further, patients showed highly localised thickening of the foveal representation in primary visual cortex, supporting the notion of aberrant pruning processes.
In summary, findings presented in this thesis allowed insights into cortical mechanisms that maximise sensitivity when visual information is sparse and clearly showed that remapping is not a general feature in achromatopsia while the absence of visual input has distinct effects on cortical structure, comparable to other patient groups with congenital loss of vision.