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Thank you Jan,
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<div class="">The BEM is a volume conduction model, and describes the geometries at which the potential distributions are computed that are the consequence of the volume currents, due to the primary currents in the brain.</div>
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<div>Yes, I thought the 3-D volume defined the position of the dipoles. I was confused by the fact that even though the BEM model is defined by surfaces, it requires to compute a volume conduction model.</div>
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<div>Anyway, I have built a tutorial for people using EEGLAB so they could use their EEGLAB datasets to perform source localization in Fieldtrip using either a volumetric or a surface MNI template source model.</div>
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<div><a href="https://sccn.ucsd.edu/wiki/A08:_DIPFIT#Advanced_source_reconstruction_using_DIPFIT.2FFieldtrip" class="">https://sccn.ucsd.edu/wiki/A08:_DIPFIT#Advanced_source_reconstruction_using_DIPFIT.2FFieldtrip</a></div>
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<div>As you could tell I am not well versed in the subtleties of source reconstruction. Feel free point to any potential error or inaccuracy. In particular, when I used minimum norm estimation on P300 data, the solution leads to extremes values on some of the
vertices. I am not sure if it is a good sign (the solution is very focal), or a bad sign (values blew up). I am caping the values for visualization purposes (which is equivalent to changing the color scale) because the max is likely within a sulcus and not
visible.</div>
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<div>cfg = [];<br class="">
cfg.method = 'mne';<br class="">
cfg.grid = leadfield;<br class="">
cfg.headmodel = headmodel.vol;<br class="">
cfg.mne.lambda = 3;<br class="">
cfg.mne.scalesourcecov = 'yes';<br class="">
source = ft_sourceanalysis(cfg,dataAvg);<br class="">
m=source.avg.pow(:,180); % plotting the result at 400 ms<br class="">
<b class="">m(m>100) = 100; % clip extreme values<br class="">
</b>figure; ft_plot_mesh(source, 'vertexcolor', m);<br class="">
view([230 0]); h = light; set(h, 'position', [0 1 0.2]); lighting gouraud; material dull<br class="">
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<div>Leads to this figure <a href="https://sccn.ucsd.edu/wiki/File:Fieldtrip_surface_solution.png" class="">https://sccn.ucsd.edu/wiki/File:Fieldtrip_surface_solution.png</a></div>
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<div>Is there a regularization parameter for the MNE method that could be tuned? I could not find any documentation on that. Anyway, if anybody can comment on that behavior, I would greatly appreciate.</div>
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<div>Best wishes,</div>
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<div>Arno</div>
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