As input for MCX, we provided an *.inp text file with relevant information for the simulation, as exemplified in ref.25. We defined the number of photons to be launched to 108. The optode position has been set in coordinates in voxel space. The original direction of the photon was placed towards the center of the image, which we defined as voxel coordinates corresponding to the origin (0, 0, 0) in MNI space. The binary volume file (*.bin) has been created from the segmented NIfTI file of interest (Colin27 or SPM12). Both time gate’s step and end were set to 5 ns to result on a single flux distribution. Voxel size and dimensions were defined according to the atlas of interest. Optodes were modelled as pencil beam (default setting in MCX). Finally we considered five different media (tissues described in Methods section), whose optical properties were set in accordance to Strangman et al.27 (Table 1).Table 1Optical properties provided as input for Monte Carlo simulations.TissueScattering (1/mm)AnisotropyAbsorption (1/mm)RefractionScalp0.720.010.0172751Skull0.920.010.0119251CSF0.010.010.0025001Gray1.100.010.0195001White1.350.010.0169001