Visual cortex stability and plasticity in the absence of functional cones in achromatopsia

Abstract

Purpose: Complete achromatopsia (ACHM) is a rare inherited disorder with non-functional retinal cone photoreceptors and a deafferented foveal representation in V1. Here we investigated whether remapping of the deafferented foveal representation to process paracentral inputs [1] is a group feature in ACHM. Such remapping might interfere with gene therapeutic treatments aimed at restoring cone function. Methods: In a multi-center study we applied fMRI assessments in a cohort of 18 ACHM individuals with confirmed biallelic CNGA3 or CNGB3 mutations and a control cohort (HC). Two independent mapping approaches, conventional phase-encoded eccentricity mapping and population receptive field (pRF) mapping, were applied for both scotopic and photopic stimulation conditions. fMRI-based measures (percentage of active V1, eccentricity, pRF size) were extracted from two anatomically defined V1 regions of interest (ROI), one ROI corresponding to the central visual field (0°-4°) and one ROI corresponding to the paracentral visual field (4°-8°). Two-way ANOVAs with the factors ROI and GROUP (ACHM vs HC) were conducted, comparing scotopic HC data to photopic ACHM data. We hypothesized that remapping associated with the lack of foveal input to V1 in ACHM would lead to a significant interaction of ROIxGROUP. Results: While there were significant effects of the factors ROI and GROUP, no significant interactions (ROIxGROUP) were observed for percentage active voxels (p = 0.7), mean pRF eccentricity (p = 0.3), or mean pRF size (p = 0.6). The results were supported by phase-encoded retinotopic data. Conclusion: Sizeable remapping of the primary visual cortex is not apparent at the group level. We suggest that while functional reorganisation of the primary visual cortex might be evident in specific individuals, it is not a general feature in ACHM.