Cortical covariance networks in ageing: Cross-sectional data from the Irish Longitudinal Study on Ageing (TILDA)

Ageing is associated with widespread alterations to the brain's anatomy and to attendant cortical networks. Yet, few studies to date have indexed anatomical covariance network differences within the age distribution of older adulthood, despite known phenotypic variation. Here, we explored cortical anatomical covariance networks in middle and older age cross-sectionally, using a large sample of community-dwelling older adults from the Irish Longitudinal Study on Ageing (TILDA). We assayed age-related anatomical changes via cortical thickness. Moreover, we explored age-related alterations in small-world and global properties of cortical thickness covariance networks, by targeting analyses towards the elder (ages 75-88; n = 88) and younger (ages 52-64; n = 95) sample members. Age, sex, and chronic disease-adjusted vertex-wise analyses revealed robust reductions in cortical thickness with age. Graph theoretical analyses of cortical thickness covariance networks revealed significantly lower betweenness centrality (i.e., network hub status) at left inferior parietal cortex in the eldest participant group as compared to the youngest. Furthermore, indices of small-worldness revealed greater lambda (i.e., less effective integration) across the right hemisphere of the eldest participant group versus the youngest. Our results are interpreted in the context of mechanisms of cortical atrophy in ageing, functional network organisation, and cognition in ageing.