[FieldTrip] Source fitting with template MRI/Headmodel

[Tommy Wilson]

Hi all,

I'm working with EEG data and I'm trying to get some basic source fitting
up and running. Unfortunately, I don't have individual subject MRIs, so I'm
using the templates provided by fieldtrip. I've co-registered my 160
Biosemi electrodes to the standard_bem template (see attached picture). For
the sourcemodel, I'm using the standard_sourcemodel3d5mm grid (picture
attached, overlaid on standard_bem). I can prepare the leadfield from there
with ft_prepare_leadfield (cfg.normalize = 'yes'), as per the LCMV tutorial.

To test this configuration, I've selected a time window in my data and
averaged across it (the covariance matrix was also calculated); the
topography of this averaged data is attached. I then attempted a source fit
with the LCMV beamformer:

cfg                     = [];
cfg.method              = 'lcmv';
cfg.grid                = leadfield;
cfg.vol                 = vol;
cfg.elec                = elec;
cfg.lcmv.lambda         = '15%';
cfg.lcmv.keepfilter     = 'yes';
cfg.lcmv.fixedori       = 'yes';
cfg.lcmv.projectnoise   = 'yes';

sourceA = ft_sourceanalysis(cfg,A);

After interpolating to the single_subj_T1.nii provided with
ft_sourceinterpolate and plotting with ft_sourceplot, I am given a
sourceplot that is highly focal in nature (see attached picture).

I'd find it very surprising if this topography were generated primarily by
a source that isn't even inside the brain (as the sourceplot indicates).
So, I'm not sure exactly where/how I'm going wrong with this one, nor am I
sure how to trouble shoot it. Any guidance you might provide would be
greatly appreciated.

Thanks so much,

Tommy
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