[FieldTrip] Problem averaging sources ("vary in the field 'inside'")

Constantino Méndez Bértolo constantino.mendezbertolo at ctb.upm.es
Tue Dec 2 18:50:11 CET 2014

Dear fieldtrippers,

We are doing beamformer with ERF acquired with an Elekta-Neuromag.
Regardless our different approaches, we always end with the same problem at
the end of the pipeline - the 'inside' field slightly varies between
subjects. I attach a plot of the difference between the inside field of two
different subjects where one can see that there are truly minor differences.

We follow the standard pipeline, I think. We use a template grid and
template mri for all the subjects, which we realign using individual
headpoints. The resulting leadfield (every subject has the same numbers of
dipoles) is used in the sourceanalysis ('lcmv'), and the difference between
pre and post periods is first interpolated (using the individual mri
aligned) and finally normalized. We also tried using volumereslice before

Individual results seem coherent but not matter what we end up with
different 'inside' fields and sourcegrandaverage complains about that. We
are using the fieldtrip-20141201 version and if we use
the fieldtrip-20111101 sourcegrandaverage does not complain about that.

I don't want to make a really complex mail so I leave it here looking
forward to hear input from anybody and willing to give more precise


Constantino Méndez-Bértolo
Laboratorio de Neurociencia Clínica, Centro de Tecnología Biomédica (CTB)

Parque Científico y Tecnológico de la UPM, Campus de Montegancedo

28223 Pozuelo de Alarcón, Madrid, SPAIN
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