Converting spherical Biosemi coordinates to Talairach

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John
Posts: 1
Joined: Fri May 27, 2011 9:53 pm
Location: McMaster University

Converting spherical Biosemi coordinates to Talairach

Post by John »

I'm trying to use sLORETA for source estimation, but the program requires that the coordinates be Talairach coordinates. We have a 128-electrode Active Two Biosemi system.

Does anyone know how to convert the spherical Biosemi electrode coordinates to Talairach, or have a link to share?

Thanks in advance,

John

bdornan
Posts: 7
Joined: Wed Jul 20, 2011 3:51 pm
Location: Sheffield

Post by bdornan »

Hey,

I'm guessing you've solved this problem by now, but I thought I'd post here to save anyone else having to spend as long as I did trying to figure this out!

As it turns out, the LORETA software (as opposed to the newer sLORETA software) has a tool to convert between BESA spherical coordinates (the format used in the spreadsheet containing the electrode locations given on the Biosemi website) and Talairach coordinates. This software is available from the same location as it's replacement (apparently I can't put a URL in my first post - google sloreta and it should be the first link)

So, first you'll need to dump the appropriate sheet of the xls file to a text document, open the LORETA software then go Electrodes Coordinate Maker (In Talairach Space) -> Based on spherical coordinates in the Schern-Berg convention. Once you've converted you can eyeball the outcome using Electrodes Viewer -> On 3D Cortical Surface - looks fine to me for the 128 electrode cap.

Hope this saves someone having as rubbish a morning as I did...

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