why scalp is so much bigger than pial?

[Long]

Hi,
Why the scalp is so much bigger that the brain cortex in this tutorial: Working with sEEG data — MNE 1.9.0 documentation
Shouldn’t be like this in reality. They should be closer then displayed in the figure.

[wmvanvliet (Marijn van Vliet)]

Good question! For some reason, the “skin” mesh of fsaverage is very large.

import mne
subjects_dir = mne.datasets.sample.data_path() / "subjects"
mne.viz.plot_alignment(subject="fsaverage", subjects_dir=subjects_dir, coord_frame="mri", surfaces=["brain", "inner_skull", "outer_skull", "head-dense"])

This could be because the fsaverage MRI is very fuzzy (it’s the average of a lot of individual MRIs after all) and the freesurfer detection of where the skin begins exactly is a bit off.

Here is what the MRI looks like in the voxel renderer of MRIcroGL:

[Long]

Thanks for your message. It makes sense to me now.