[FieldTrip] LCMV beamforming, source.avg.pow is not the power?

Ta Dinh, Son son.ta.dinh at tum.de
Tue Jan 10 08:20:58 CET 2017

Hi Fieldtrippers,

I have been trying to do a source analysis on my (resting-state) data using LCMV beamforming and as part of a sanity check, I wanted to plot the alpha power.

Using ft_sourceanalysis I get a source structure containing avg.pow and intuitively I expected this field to contain the averaged power of the time series. Therefore, I band-passed the data on the sensor level before doing the LCMV source reconstruction.

Surprisingly however, when I used the resulting LCMV spatial filter to construct virtual channels and calculated the alpha power spectrum of the resulting time series using ft_freqanalysis, the average power between these 2 approaches differed by several orders of magnitude over many voxels.

Did I make some conceptual misunderstanding? Are the 2 approaches I used not equivalent? Or does source.avg.pow not contain the average power at all?

Any comments would be greatly appreciated!

Best regards,

Son Ta Dinh, M.Sc.
PhD student in Human Pain Research
Klinikum rechts der Isar
Technische Universit√§t M√ľnchen
Munich, Germany
Phone: +49 89 4140 7664<tel:%2B49%2089%204140%207664>

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