[FieldTrip] Source localization of MEG resting state data

[Tzvetan Popov]

Hi MK CHOE,

Q1; please call ft_sourcedescriptives before ft_sourceinterpolate or cfg.keeptrials = ’no’; during the call to ft_sourceanalysis.
      What do you mean by “weird output”? 
Q2; If you think of GOF and the like, not really. Sometimes one can take the scalp topography into account and compare the sensor and source level outputs.
      One way to go is also to split the continuous data into high and low signal pseudo epochs and make a beamformer contrast on the high and low power. 
How to do so is illustrated here: http://www.fieldtriptoolbox.org/tutorial/networkanalysis

Good luck,
Tzvetan


 

> Dear fieldtrip users,
> 
> I tried using DICS beamforming on MEG resting state data of healthy controls.
> (e.g. no task, no baseline, eyes opened)
> 
> I analyzed to localize oscillatory sources using beamformer techniques according to the following tutorial. 
> (link: http://www.fieldtriptoolbox.org/tutorial/beamformer)
> However, the output image was weird to be considered as resting data. I would like someone to help me through source localization procedure.
> 
> 
> Q1. Is there something wrong in my script as below? 
> cfg             = [];
> cfg.output      = 'powandcsd';
> cfg.method      = 'mtmfft';
> cfg.foilim      = [8 12];
> cfg.tapsmofrq   = 2;
> cfg.channel     = {'MEG'};
> cfg.keeptrials  = 'yes';
> fft_rest = ft_freqanalysis(cfg, data_clean); % resting state MEG data (after preprocessing)
> 
> %% Computing the leadfield matrices
> cfg             = [];
> cfg.grad        = fft_rest.grad;
> cfg.vol         = vol;  % head model
> cfg.grid        = grid; % source model
> cfg.keeptrials  = 'yes';
> cfg.normalize   = 'yes'; 
> cfg.channel     = {'MEG'};
> rest_grid  = ft_prepare_leadfield(cfg);
> 
> %% Source analysis 
> cfg             = [];
> cfg.frequency   = 'all';
> cfg.grad        = fft_rest.grad;
> cfg.method      = 'dics';
> cfg.grid        = rest_grid;
> cfg.vol         = vol;
> cfg.keeptrials  = 'yes';
> cfg.keepfilter  = 'yes';
> cfg.dics.lambda = 0;
> cfg.dics.projectnoise = 'yes';
> rest_source = ft_sourceanalysis(cfg, fft_rest);
> 
> mri_slice = ft_volumereslice([], mri) %mri: volumesegmented mri
> cfg            = [];
> cfg.parameter = 'avg.pow';
> rest_sointer   = ft_sourceinterpolate(cfg, rest_source, mri_slice);
> 
> 
> Q2. Is there any way to check whether the beamforming is performed well?
> 
> Any help would be greatly appreciated.
> 
> MK CHOE
> 
> -- 
> Mi Kyung CHOE
> Department of Brain & Cognitive Sciences, Seoul National University 
> Human Brain Function Laboratory
> E-mail : cmk0803 at hbf.re.kr, cmk0803 at meg.re.kr
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