= OpenMEEG BEM head model =
This forward model uses a symmetric boundary element  method (symmetric BEM) and was developed by the French public research institute INRIA ([[http://www-sop.inria.fr/athena/software/OpenMEEG/|website]]).  It uses three realistic layers (scalp, inner skull, outer skull). The goal of this forward solution is mostly for EEG users, to provide a better model than the existing "3-shell sphere". It is not necessary for MEG  users, as the "overlapping spheres" method gives very similar results  but much faster. Nevertheless, for demonstration purpose, we are going to compute this solution on MEG recordings.

== BEM surfaces ==
We need three realistic layers extracted from the subject's MRI (scalp, inner skull, outer skull), plus the source space (cortical surface). Those layers are sometimes complicated to generate. In the case you do not have any way to calculate the inner skull and outer skull surfaces, Brainstorm can generate rough approximations based on the subject's cortex and head surfaces and Colin27's inner and outer skull surfaces.



It provides for EEG a much better  forward solution than the previous "3-shell sphere" model. EEG users  should try to switch to this method quickly.