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

Tzvetan Popov tzvetan.popov at uni-konstanz.de
Mon Feb 27 14:23:42 CET 2017


Hi Thomas,

you might have solved it. In case not, I changed :
cfg.relnoise = 5;

and the amplitude of the baseline signal to

cfg.dip.amplitude = .1; 

and it worked. You simulate the location at 9 0 6 and it comes out (NAI) at 90.5 -.5 59.5 (see attached). 

best 
tzvetan




> 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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