Voxel-based morphometry (VBM) analysis was performed using the default protocol for the VBM8 toolbox for SPM8 (http://dbm.neuro.uni-jena.de/vbm/). The T1 images were spatially normalized using the high-dimensional DARTEL normalization and segmented into grey matter, white matter and cerebrospinal fluid. Further, non-linear effects of the normalization were modulated so that GMV values describe the amount of grey matter relative to the voxel size. For example, if two grey matter voxels are squeezed into a single voxel, then the modulated value would be two because one normalized voxel would describe two grey matter voxels in native space. Further, sample homogeneity and segmentation results were examined to identify any outliers in the study sample but no images required exclusion. As a final step, modulated images were smoothed with an FWHM of the Gaussian smoothing kernel of 8 × 8 × 8 mm.
