Voxelwise differences between patient groups in rates of cortical thinning over time. Image overlays are t-statistic maps for the interaction of each group with time, calculated from LME models and thresholded at voxelwise P < 0.001 with a minimum cluster volume of 600 µl, corresponding to a corrected cluster-wise threshold of P < 0.05. Warm colours indicate that cortical thinning over time is more rapid in the second group than the first; cool colours indicate that cortical thinning is more rapid in the first group than the second. aAD = amnestic Alzheimer’s disease; fvAD = frontal variant Alzheimer’s disease.