[FieldTrip] Deviations in Inverse Solutions between Fieldtrip and MNE-C packages?

[Burkhard Maess]

Dear Frieldtrip experts,

since I like to use freesurfer segmentations and the nicely prepared
coupling with MNE, I took some effort to import those volume conductors
and source space models into fieldtrip as well. This seems to work as
fas as it concerns the geometric representation in space (the
coregistration - pp04a_volume_sources.png). The coregistration was made
via MNE-C and also imported into fieldtrip. In summary, I am using the
same model (volume conductor + source space), the same coregistration
and the same data.

For visualization, I have attached figures made by either MNE-C or by
matlab/fieldtrip. In general, all attached jpg-files were generated
using MNE-C and all png-files were produced by matlab/fieldtrip.
Attached figs can be downloaded from this file share:
https://owncloud.gwdg.de/index.php/s/19WpPrV5Dw0gD28

Using sloreta as the inverse method, there is also a reasonable match
between both packages of software. Please check the attached files
pp04a_sloreta_90ms*.{jpg,png} .

However, what is when using a different method, e.g. minimum norm
estimates? Please see the corresponding pics: pp04a_mne_90ms*.{jpg,png}.
The MNE solution estimated via MNE-C is similar to the sloreta solution.
Fieldtrip, however, estimates something completely different. The MNE
solution by fieldtrip rather appears to have some meshing problem, or
so? The same pattern can also be observed for different subjects' data.
Fieltrip also offers eloreta as a method - again a different solution,
but also very unexpected (no figs attached, though).

What could be possible reasons for this unexpected behaviour?

Regularization? Covariance matrices? Here is the relevant part in my
matlab script which switches between the methods. Which options do I
need to activate in case of the 'mne'-method or the 'eloreta' method -
both deviating strongly from the expected solution.

%% Source localization using different methods
% sourcemethod      = 'sloreta';
% sourcemethod      = 'eloreta';
sourcemethod      = 'mne';
cfg               = [];
cfg.method        = sourcemethod;
cfg.grid          = leadfield;
cfg.headmodel     = headmodel;
cfg.latency       = 'all';
cfg.mne.lambda      = 0.03;
cfg.eloreta.lambda  = 0.03;
cfg.sloreta.lambda  = 0.03;
source            = ft_sourceanalysis(cfg, tl);

If needed, I could share all data files needed to run the same analysis
on your computer.

Hints would be much appriciated - thank you very much in advance,

all the best,

Burkhard






-- 
Dr. Burkhard Maess
Brain Networks (@brainnetleipzig)
Max Planck Institute for Human Cognitive and Brain Sciences
Stephanstr. 1a, D-04301 Leipzig, Germany
phone/fax: +49 341 9940-2526/-2511   mail: maess 'at' cbs.mpg.de,   http://www.cbs.mpg.de