[FieldTrip] Create BEM model for EEG source localisation

Maria Pefkou Maria.Pefkou at unige.ch
Mon Mar 26 18:01:00 CEST 2012

Dear FieldTrip users,

I started using the toolbox fairly recently to analyse EEG data and I have
huge trouble making a BEM model, which I need for source localisation.
Following the online tutorial, I processed my subjects' individual
structural MRIs in FreeSurfer and MNE and managed to prepare the
triangulated mesh. However, my problem is the volume conduction model. I
can get a singleshell one, using the ft_prepare_singleshell function, but
as far as I understand it is excusively used for MEG data. I came to this
conclusion because when I try to compute the forward model, given that I
provide information about the electrodes position, I always get the
following error:

"unsupported volume conductor model for EEG".
I guess this is because the vol.type is 'nolte' and there is no such case
for EEG data, at least not in the ft_prepare_vol_sens.m function, which is
automatically called.

I have tried to prepare a BEM model using the ft_prepare_headmodel function
with cfg.method='bemcp' or cfg.method='dipoli' but I was unsuccessful.
The problem is that, after having tried various functions/options, I lost
the general picture and I'm running in circles... The question is: I have a
segmented mri, how can I get a BEM model out of this? I must be missing a
fundamental part of the procedure but I can't quite find out what it is.
Any suggestions/help would be very much appreciated.

Thank you in advance,
Maria Pefkou

Research Assistant
Functional Brain Mapping Lab
University of Geneva
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