= 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, using the existing TutorialCTF protocol.

{{attachment:openmeeg.gif||height="75px",width="274px"}}

== 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.The surfaces created with Brainstorm are by construction non-intersecting.

 1. Select the TutorialCTF protocol
 1. Go to the anatomy view (first button on top of the database explorer)
 1. Right-click on Subject01 > Compute BEM surfaces...You can set the approximate number of vertices you want for each layer. Leave the default parameters and click on Ok.<<BR>><<BR>> {{attachment:bemPopup.gif}} {{attachment:bemOptions.gif}}
 1. At the end of the process, three new surfaces are added to the in the database:<<BR>><<BR>> {{attachment:bemFiles.gif}} {{attachment:bem3d.gif}}

== Forward model ==
 1. Switch to the view "Functional data (sorted by subjects)"
 1. Right-click on Subject01 / Right > Compute head model. Select OpenMEEG BEM in the list.
 1. Click on Run

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.