Electrode registration when loading EEGLAB dataset in Brainstorm

Hello All,
When I load this file (https://www.transfernow.net/01joy1o0050a) in Brainstorm, I am getting this message below:

I am not familiar with electrode registration and this worries me as there might be something wrong with the electrode positions which I cannot identify. I am not sure what this message means especially as regards to digitisation and fiducials. The electrodes were imported originally into EEGLAB using standard 10/10 electrode positions and that is all.

And what exactly does the message ('Refine registration now?') wants me to do. Should I use the 3D display (shown below) of electrode positions to realign the electrodes if they seem not to be in their correct positions as per the labels? When I click yes the electrodes seem to be adjusted automatically although I am not sure if I need to do anything after that. I also just do not understand why the original standard electrode positions loaded in EEGLAB might be inaccurate in Brainstorm.

I am interested in doing source localisation over these electrodes; I hope I will not have any issue as long as the electrode look visually in the right positions in Brainstorm 3D electrode display?? I just do not want source localisation results to be affected by electrode positioning problem which I am unaware.

Thanks for any clarifications. Sorry if these are very basic questions.

I guess you are using non-realistic electrode positions from EEGLAB.
What you import here is not something that matches the real head shape of the template (ICBM152), it is a set of spherical points only used for visualization in EEGLAB.

You need to import correct 3D positions for your electrodes. You have three options:

  • if you have a real digitized head shape of your subject, import the positions in Brainstorm as show in the EEG tutorial
  • otherwise, you can use one of the template EEG cap available in Brainstorm (right-click on the channel file > Add EEG positions > ICBM152 > …)
  • last option, not recommended because of its randomness: edit the positions you got from EEGLAB to fit the head of the subject (right-click on the channel file > MRI registration > Edit)

I recommend you start by reading the introduction tutorials (section “Get started”, at least until #23 if you want to do source analysis, using the example dataset provided with the tutorial). The read the tutorial “EEG & Epilepsy” for additional details about EEG.