[Eeglablist] DIPFIT Biosemi MNI head model coordinates

[James Jones-Rounds]

Hello Abigail,

I spent some time looking for the same thing you are, I think. I'm assuming
you have electrode coordinates from the BioSemi website, but that what
you're looking for is how to manually coregister them to a dipfit head
model. I found some assistance in an eeglablist post last year, linked here
<http://sccn.ucsd.edu/pipermail/eeglablist/2012/005354.html>

I don't know if you have an ABC or 1020 electrode montage, but for the ABC
montage, I needed to put in the following dipfit settings in order to get
the montage to fit the 4-shell BESA head model (as I have no MRI scans to
use):

EEG = pop_dipfit_settings( EEG,
'hdmfile','C:\\...\\eeglab\\plugins\\dipfit2.2\\standard_BEM\\standard_vol.mat','coordformat','MNI','mrifile','C:\\...\\eeglab\\plugins\\dipfit2.2\\standard_BEM\\standard_mri.mat','chanfile','C:\\...\\eeglab\\plugins\\dipfit2.2\\standard_BEM\\elec\\standard_alphabetic.elc','coord_transform',[0
-15 0 0.1 0 -1.5708 103 90 100] ,'chansel',[1:132] );

The Coordinate Transform part took the most trial and error, and here is
the explicit description for what I put in each GUI box (when you're in the
"manual co-registration" step):

-pi/2 radians yaw for z-axis roll; -15mm move 'front' for y-axis; 0.1
radians pitch for x-axis; resize - {x} 103; {y}90; {z}100

Good luck!

James


-- 
James Jones-Rounds
Laboratory Manager
Human Development EEG and Psychophysiology (HEP) Laboratory,
Department of Human Development,
--------------------------------------------
Cornell University | Ithaca, NY
607-255-9883
eeg at cornell.edu
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