[FieldTrip] neuromag306 sources look vertically smeared.

[Hanneke van Dijk]

Dear all,

My data (that are recorded with a neuromag306 system) look vertically
smeared after sourceanalysis (see attached picture). The sources look like
columns. The location (when plotted with method 'surface') looks comparable
to the sensor analysis so I am not worried about that.

The noise projection (cfg.dics.lambda) is something that I have been
playing around with, but other then 'nai amplitude' de- or increases, this
does not change the sources 'verticallness'. This indicates to me that this
might be the problem...

I am wondering if any of you has an idea where I should look to find a
solution.

Further information:

I am using a mni-normalised headmodel such as described on the site:
http://fieldtrip.fcdonders.nl/example/create_single-subject_grids_in_individual_head_space_that_are_all_aligned_in_mni_space
but
adapted to the neuromag system (I will make changes to the specific site
:-) ).

Then compute the fourier, and do sourceanalysis as follows:

cfg                     = [];
cfg.method              = 'dics';
cfg.grid                = mni_grid;
cfg.grid.filter         = source.avg.filter; % precomputed filter and
leadfield to project all trials through the same filter
cfg.grid.leadfield   = source.leadfield;
cfg.vol                 = ft_convert_units(mni_vol,'mm'); % this step is
needed somehow...
cfg.vol.unit           = 'cm';
cfg.frequency       = 60;
cfg.latency           = 3;
cfg.dics.projectnoise   = 'yes';
cfg.dics.lambda         = '0.05%';
cfg.dics.normalize      = 'yes';
cfg.keeptrials          = 'yes';
cfg.rawtrial            = 'yes';      % project each single trial through
the filter
s = ft_sourceanalysis(cfg, f);

Thanks in advance for any suggestion!

Groetjes Hanneke
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