Dear Francois,
Thanks so much for your quick and helpful reply!
I would have 2 short follow up questions:
1.In that case, I assume a workaround (although computationally very expensive) would be to first perform a source inversion of the EEG signal, and then compute the regressions at source level?
2. What about arithmetic differences in EEG amplitude between 2 conditions? These are not 'actual' EEG signals anymore and might have very different statistical properties than the original data. is it also problematic to compute sources for such condition differences?
Many thanks again for your help!
Ulrich