The assessment of the main effects of APOE ε4 and SVD-based tau scores on cortical thickness at each vertex was carried out by statistical inference over the coefficients in a voxelwise linear model with interaction terms.

The reduction in cortical thickness was more related to tau than with β-amyloid scores, particularly in the precuneus, posterior cingulate cortex, and entorhinal cortex (top panel). Neither APOE ε4 nor the interactions tau x APOE ε4 and β-amyloid x APOE ε4 showed areas of strong statistical significance. Similarly, the interaction tau x β-amyloid did not show a significant effect on cortical thickness.

The reduction of cortical thickness associated with tau remained statistically significant after accounting for the concurrent effect of β-amyloid, particularly within the entorhinal cortex and posterior cingulate cortex. Such a relationship seems to be stronger in magnitude and spatial extent than the corresponding tau-FDG association (middle panel).

The effect of tau on cortical atrophy was consistent in spatial location across the different measures of atrophy. Among all different atrophy measures, cortical volume is the one showing the weaker association with tau. In contrast, cortical thickness turns out to be the atrophy measure that showed the stronger and more spatially extended association with tau, supporting the idea that the most significant tau-related anatomical changes of the cortex occur along the trajectory of the cortical columns.