[FieldTrip] calculate DICS Beamformer on a group level?

[christian.merkel at med.ovgu.de]

Hello,


I hope some of you can give me some advice regarding a more conceptual problem with localizing specific oscillations within MEG data:

I wanted to use the DICS-approach to localize a specific spectral effect in my MEG-data within the source space. Now I don't know whether this can be done on an averaged dataset across multiple subjects, since in this case the cross-spectral-density matrices of all the subjects would have to be averaged as well and I am not sure whether such an averaged CSD-matrix still makes sense.

In more detail, I have spectral timeseries (complex) of several seconds within one specific frequency-band (sens x time). I calculate the grand average across time to get the evolution of the topography of this effect over time. Additionally, I ran a PCA on that averaged timecourse to extract the specific source (component) in sensorspace that I am interested in. Then I used the resulting unmixing-matrix to multiply that components weights with each subjects timecourses (sens x time). Thus I have one overall topography of that effect in sensorspace and its timecourse + variance (which I can run statistics on). Now I thought I can also look for the same effect in sourcespace but I actually just have the topography without the CSD-Matrix. And even if one could average the single-subjects CSDs, how would I retain the CSD for a specific component after a pca?


Thanks for any help,


Christian M.