In addition to the Colin27 head model, which is based on 27 averages of a single subject, we have considered a second head atlas based on the tissue probability maps provided in SPM12. These maps have been generated based on 549 subjects from the IXI dataset18. The specific subjects used to compute TPM.nii can be found in spm_templates.man19. We spatially resampled20 the TPM.nii image from 1.5 × 1.5 × 1.5 mm3 to 2 × 2 × 2 mm3 and followed the same procedure as for Colin27 to obtain the segmented image (herein called “SPM12”), illustrated in Fig. 2B.