For group analyses, the following procedures were applied. (1) T1-weighted sMRIs from each subject (Fig. 1A) were registered to MNI space (Montreal Neurological Institute, MNI-152 atlas as in Fig. 1B) using an affine transformation (FLIRT–FMRIB's Linear Image Registration Tool) (Jenkinson and Smith, 2001) in FSL (www.fmrib.ox.ac.uk/fsl/). (2) The cortical (Fig. 1C) and subcortical masks with pre-defined brain regions from the standard atlas were transferred to the individual's headspace (Fig. 1D), using the inverse of the transformation obtained in the first step: the Harvard-Oxford Atlas, part of the FSL software with masks of 96 cortical gray-matter regions (48 regions in each hemisphere), 21 sub-cortical regions, and cerebellum, was used. (3) The regional masks were down-sampled to a cubic source grid with voxels of 5 mm per side (Fig. 1E). (4) VESTAL MEG source imaging used the source grid from step 3. This step permits group-based analyses. In the shown example, MEG responses evoked by S1 localized to left and right Heschl's gyri (Fig. 1F). (5) Finally, for regions of interest (ROIs), the source time course was obtained by summing activity from all ROI voxels. Fig. 1H shows the time course from left Heschl's gyrus (dark blue region in Fig. 1C and D).
cortical gray-matter regions
96
regions
48
sub-cortical regions
21
cubic source grid
voxels
5 mm per side
mm per side