MEG data were co-registered with participants MRI structural scan by matching the digitized head shape data with surface data from the structural scan (Jenkinson and Smith, 2001). The aligned MRI-MEG image was used to create a forward model based on a single-shell description of the inner surface of the skull (Nolte, 2003), using the segmentation function in SPM8 (Litvak et al., 2011). The cortical mantle was then extracted to create a 3D cortical mesh, using Freesurfer v5.3 (Fischl, 2012), and registered to a standard fs_LR mesh, based on the Conte69 brain (Van Essen, 2012), using an interpolation algorithm from the Human Connectome Project (Van Essen et al., 2012; instructions here: https://goo.gl/3HYA3L). Finally, the mesh was downsampled to 4002 vertices per hemisphere. Due to the extensive computation time involved in these procedures, all participant-specific cortical meshes are available to download in the /anat directory of the Figshare repository (see later).
