How can I manually set a reference electrode from the Brainstorm interface?

Hello François,

I am a new Brainstromer, and I would like to know if it is possible for me to set manually a pair of electrodes from my custom Emotiv EPOC+ EEG cap as 2 reference channels.
Context: I am currently using the default ICBM 152 anatomy. I generated a 46704V iso2mesh/MergeSurf FEM mesh from the 3 head/outerskull/innerskull surfaces. Then, I imported my 16-channel Emotiv EPOC+ EEG cap configuration (including both the P3/P4 (CMS/DRL) reference channels). Now, I would like to compute a head model using DUNEuro FEM (volume) that generates a 14-rows Gain matrix, with the two missing rows corresponding to P3 and P4.
What I can see now, after computing my head model, is that Brainstorm sets the first row of my 16-rows Gain matrix to 0 (I am not sure if the order in which the 16 electrodes are stored in my channel file, and the one in which the 16 rows of my Gain matrix are displayed, are the same).
Does it mean Brainstorm considers my AF3 channel as the unique reference channelby default?
I read what you answered here Reference Electrode - #5 by Francois but I am still unsure of what I should do.
Channels Gain
Thank you for your help!
Best,
Valentin

I am a new Brainstromer, and I would like to know if it is possible for me to set manually a pair of electrodes from my custom Emotiv EPOC+ EEG cap as 2 reference channels.

If you want to re-reference your EEG recordings to the average of the P3+P4 electrodes:

Now, I would like to compute a head model using DUNEuro FEM (volume) that generates a 14-rows Gain matrix, with the two missing rows corresponding to P3 and P4.

The EEG inverse solutions are always computed from EEG recordings in average reference. No matter which referencing scheme you transform your data into before, the data will be re-converted to an average reference before the computation of the minimum norm solution.

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Thank you very much François for your quick and very informative reply!