[VBMEG-users:00203] Volume conductor model

[Joris van der Cruijsen]

Dear VBMEG users,

Can anyone clarify the modelling choice for the 3-layer volume conductor used for EEG source reconstruction? The VBMEG-implemented BEM model consists of three layers (scalp, skull and CSF, with corresponding conductivities); however, other 3-layer implementations such as Fieldtrip or OpenMEEG describe 3-layer models consisting of scalp, skull, and brain (with corresponding conductivities). Are there any specific reasons for the VBMEG toolbox not to model the brain but define only a CSF layer?

Best regards,
Joris

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[Yamashita Okito]

Dear Joris

In VBMEG, the EEG leadfield of the three layer volume conduction model
is actually calculated with the scalp, skull and brain similar to the
other toolbox. More precisely, we define the inner-most surface of the
three layer volume conduction model, which VBMEG labels "CSF", as a
FreeSurfer extracted cortical surface expanded by 3mm. When computing
the leadfield, the conductivity value inside this surface is assumed to
be the conductivity of grey matter (which is the same value to skin
conductivity in default).

Best regards
Okito Yamashita