[FieldTrip] Aligning electrodes to template head model

Wu, Jia jia.wu at yale.edu
Tue Sep 15 05:00:33 CEST 2015


What a coincident. I'm also working on source analysis on EEG data using GSN HydroCel 128. I had a post a couple weeks ago about later steps. But I did get the alignment to work. The picture you posted looked like the status before the alignment. So i suspect that alignment did not happen.

I'm not sure whether you have noticed it, but the fiducial positions in elec location file were called 'FidNz', 'FidT9', 'FidT10', instead of 'Nz','LPA','RPA' as in the tutorial. So they need to be changed. Then the alignment should work.


From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Helen Wieffering [helen.wieffering at gmail.com]
Sent: Monday, September 14, 2015 4:46 PM
To: FieldTrip discussion list
Subject: [FieldTrip] Aligning electrodes to template head model

Hello all,

I have a quick question on aligning electrodes to the standard_bem headmodel, which I downloaded from the FT server.

Namely, are the standard_mri and the standard_bem in the same coordinate system? I assumed this would be so, since one was developed from the other. But when I try to align my electrodes to the standard_bem volume using fiducial positions from the standard_mri, I get very strange results: (image below and attached)

[Inline image 1]

I'm using a GSN HydroCel 128 Cap, and my elec structure contains the fiducial positions relative to the electrodes.
I've been following the tutorial at http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.fieldtriptoolbox.org_tutorial_headmodel-5Feeg&d=AwMFaQ&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=9ehCplyXHP0-m9ayYv1FOg&m=wNRiA8CLR4Y1ZrEaTkTaIoVaUczL5TYuWIx6FyQDphg&s=LjU77qpw8I7LnSHIEQrNIB0R0YLrutfAEtjjOMjBys0&e=> and would like to follow the steps under 'Automatic Alignment', but as I said: pulling the fiducial positions from the standard_mri seems to not work with the tutorial steps.

Any help is appreciated - thanks in advance!

Helen Wieffering
Bowdoin College
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