Tissue properties of optic radiations representing the foveal and peripheral visual fields.

The biological properties of the foveal and peripheral visual pathways differ substantially. Here, we compared tissue properties of optic radiations (OR) carrying foveal and peripheral information to primary visual cortex (V1), measured with diffusion MRI (dMRI). We analyzed dMRI in two datasets: the Human Connectome Project (HCP; n=180; age 22-35) and the UK Biobank (UKB; n=7,088; age 45-81). In the HCP, OR was delineated using a three-dimensional atlas; parts of OR representing fovea and periphery were divided based on V1 fMRI responses close to OR endpoints. (2) In the UKB, OR was delineated using landmarks and divided using anatomically-based estimates of V1 responses close to OR endpoints. The dMRI signal was modeled using a kurtosis model, which provides information about tissue microstructure. Despite differences in data collection, population characteristics, and analysis methods, both datasets revealed higher fractional anisotropy, lower mean diffusivity, and higher mean kurtosis in the foveal OR than in peripheral OR, consistent with denser nerve fiber populations in foveal pathways. In further analysis of the UKB, we found that age is associated with increased diffusivity and decreased anisotropy and kurtosis, consistent with decreased density and tissue organization with aging. However, anisotropy in fovea decreases faster with age than in periphery, while diffusivity increases faster in periphery, suggesting foveal and peripheral OR differ in terms of aging.