[FieldTrip] Help Regarding the Source Level Connectivity

[Schoffelen, J.M. (Jan Mathijs)]

Hi Kaniska,

Welcome on board! With respect to source level analysis of connectivity I would like to suggest and recommend NOT to use the rawtrial (or singletrial) options in ft_sourceanalysis. This corner of the code is not particularly robust. Rather I would use a combination of ft_sourceanalysis (with cfg.<method>.keepfilter = ‘yes’;) and ft_virtualchannel, to get the single trial signal time courses, followed by a downstream post processing of the virtualchannel data to obtain a connectivity estimate.

This being said, I think that the cause of the error that you get may be due to the fact that you try to compute a frequency domain measure of connectivity based on time domain input (since you used lcmv). Coherence requires frequency domain data as input (as can e.g. be obtained with cfg.method = ‘pcc’ or ‘dics’ in ft_sourceanalysis, but PROVIDED you have used ft_freqanalysis first on the time domain data). Alternatively, you’d need to spectrally transform the source level single trial time courses (as obtained with lcmv, mne or whatever) before supplying the result to ft_connectivityanalysis.

Best wishes,
Jan-Mathijs


On 6 Mar 2024, at 22:20, Kaniska Samanta via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:

Hi all,

I am new in using fieldtrip toolbox and source level connectivity analysis. I have constructed source form MEG data (Elekta Neuromag Triux system with 306 channels) by using LCMV beamformer technique (method = 'rawtrials'; to construct source level momentums for each individual trial).

Now when I try to compute brain connectivity using 'ft_connectivityanalysis' using method as 'coh' and complex as 'imag', I am getting the following error,

<image.png>

please not I have 300 trials and the signal length is 401. And I have 67 sources.

<image.png> <image.png>

In the documentation of 'ft_connectivityanalysis' it has been mentions that 'coh' supports source data and I have no idea why I am getting the error. I am using the following code snippet for connectivity,

cfg = [];
cfg.method = 'coh';  % Compute coherence
cfg.complex = 'imag';  % Compute imaginary part of coherence
coh_results = ft_connectivityanalysis(cfg, source);

Can anyone please help me out to get it sorted?

Thanks in advance.

Best Regards,
Kaniska Samanta
PhD Researcher, Intelligent Systems Research Center (ISRC)
Ulster University
Derry~Londonderry, Northern Ireland, United Kingdom



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