Hi,
I am defining single equivalent dipole localization using the dipfit_erpeeg() function with eeglab during a generalized seizure. I do that in a loop for each sample (sampling freq is 256 Hz) of the seizure, and then I plot all the dipoles on the MNI BME head model I use to define the dipoles. As you can see from the picture shown here (dots represent dipole position; color of dots represent time (white t0 - dark brown 7 s), size of dots represent residual variance for each dipole fit) a couple of dipoles are positioned outside the head map. I do not understand how can some dipoles be positioned outside the head model used to fit the dipoles. Is anybody familiar with these results and can explain why this happens?
Thank you a lot in advance for your help!
Best,
Valentina
Hi,
first, I am not an expert on this, so please take my answer with an appropriate amount of salt. As far as I understand source localization, there are two main ways for the dipoles to be located outside the head. The first is an artefact of the localization proceedures, where whatever software you used plots the dipole outside of the head due to some misalignment or erroneous interpolation of the location using the mesh that represents the head. The other is that there are some artifacts in the data that originate outside of the head and are thus fitted there.
As far as I have been able to understand, the first option is more likely, maybe some of the attached sources can be of help;
Article Taking the EEG Back Into the Brain: The Power of Multiple Di...
- https://www.fieldtriptoolbox.org/faq/sticking_out/
- https://eeglab.org/tutorials/09_source/DIPFIT.html
- https://www.biorxiv.org/content/10.1101/2020.07.01.181875v1.full
Hope this helps you somewhat.
Jakob Sajovic
Thanks a lot for your answer!
Yes, the first option was also what I was thinking about, given that I use a standardized head model.
Thanks was more, that was very helpful!
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