[FieldTrip] beamforming pipeline & comparing sources between groups of participants?

[Ioanna Zioga]

Dear Vladimir,


For anyone interested, I used SPM to make a template head model which I'm going to use to do beamforming in FT.

I have queries with regards to the source analysis pipeline I'm using in FT, as the results I get don't seem right.


Vladimir, following our previous email exchange (and thanks to your suggestions), I have now managed to compute the lead field matrix in FT (by removing eeglab and fieldtrip directories from the path, and adding spm's).


I want to contrast the sources of two groups of participants (high- vs. low-learners) in two frequency bands (low: 2.5-4.5 Hz; high: 12-32 Hz), from 0.20-1 sec post stimulus onset.


Here is my pipeline:


% Calculate the cross spectral density matrix (e.g., for the 12-32 Hz frequency band)

cfg                    = [];
cfg.method     = 'mtmfft';
cfg.output       = 'powandcsd';
cfg.foilim         = [22 22];
cfg.taper          = 'dpss';
cfg.tapsmofrq = 10;
cfg.keeptrials   = 'yes';
cfg.keeptapers = 'no';
cfg.toi                = 0.6;
cfg.t_ftimwin   = 0.4;
freq                    = ft_freqanalysis(cfg, EEGft);


% Source analysis using DICS beamformer
cfg                      = [];
cfg.headmodel = vol1;
cfg.grad             = sens1;
cfg.senstype     = 'eeg';
cfg.grid              = grid;
cfg.method       = 'dics';
cfg.frequency   = [12 32];
cfg.latency        = [0.2 1];
cfg.dics.projectnoise   = 'yes';
cfg.dics.lambda            = 0;
cfg.dics.keepfilter        = 'yes';
cfg.dics.realfilter          = 'yes';
sourceA                         = ft_sourceanalysis(cfg, freq);

% Plot sources
cfg                           = [];
cfg.method            = 'slice';
cfg.funparameter = 'pow';
ft_sourceplot(cfg, sourceA);

=> The source plots look weird though - they scale from 0 to x10^45, and are totally black.


1) Am I doing something wrong in the freqanalysis or the sourceanalysis?

2) Do I need to do the ft_sourceanalysis separately for each participant?

3) Is there a way to average the results of the source analysis over groups of participants?

4) Could you give any direction/resource on how to statistically compare the sources of different groups?


As you all know this is a very exciting but also not trivial analysis.. so I'd be extremely grateful for any help at this point, it'd be very much appreciated! Thanks so much in advance!


Best,

Ioanna

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https://doi.org/10.1371/journal.pcbi.1002202