[FieldTrip] simulating a dipole with a real headmodel and using DICS to locate it misplaces the source

Thomas Hartmann thomas.hartmann at th-ht.de
Fri Feb 24 18:33:52 CET 2017


hi,

i wanted to see whether i can simulate a dipole with the data provided 
by the tutorial and use the DICS beamformer to see where the source gets 
projected.

the code i used is in the attached file.

it expects the data you can download from here: 
ftp://ftp.fieldtriptoolbox.org/pub/fieldtrip/tutorial/beamformer/

in a folder called "beamformer".

the puzzling thing is that i do not seem to manage to have it project 
the sources anywhere near to the original dipole in the simulation. the 
center of the head bias come out nicely if neither baseline correction 
or NAI calculation is used. i also checked whether the the coordinate 
system of the volume and the grid i generate match. i also checked 
whether the chosen dipole shows up at the correct location when i plot 
it on the head model.

so, my question is: what do i not get here? maybe there is something 
wrong with my script? maybe ft_dipolesimulate is not supposed to be used 
that way?

i would really appreciate any suggestions.

best,
thomas

ps: i also tried with eloreta and a simple dipole fit. the results look 
slightly different but not really any better...

-- 
Dr. Thomas Hartmann

Centre for Cognitive Neuroscience
FB Psychologie
Universit├Ąt Salzburg
Hellbrunnerstra├če 34/II
5020 Salzburg

Tel: +43 662 8044 5109
Email: thomas.hartmann at th-ht.de

"I am a brain, Watson. The rest of me is a mere appendix. " (Arthur Conan Doyle)

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