[Eeglablist] Bipolar montage channel location question

[Delorme, Arnaud]

Dear Babak,

> I am working on a sleep eeg dataset with bipolar montage. I can not find channel location for bipolar montage on eeglab and besa doesn't accept these channels too. I need to determine electrodes position for further analysis such as extracting topographical map. I read some of your references and asked mr delorme about it, he answered me briefly in his webinar presentation but i am not sure wheter I underestood the soltion correctly or not. Please correct me if i am wrong.
> To solve this problem I should first rerefrence all channels with average rereference

You first need to reference to a common reference. You will need to do this in a script because EEGLAB cannot handle daisy chain montages. So if you have 4 channels in a daisy chain montage:

C1: FP1-FP2
C2: FP2-FPz
C3: FPz-Pz
C4: Pz-Oz

To reference all channels to Pz (for example, do)

C1': C1+C2+C3 (FP1-Pz) or EEG.data(1,:) = EEG.data(1,:)+EEG.data(2,:)+EEG.data(3,:);
C2’: C2+C3 (FP2-Pz) or EEG.data(2,:) = EEG.data(2,:)+EEG.data(3,:);
C3’: C3 (FPz-Pz)
C4’: -C4 (Oz-Pz) or EEG.data(4,:) = -EEG.data(4,:);

Now all channels are referenced to Pz (and you can then compute average reference if you want to).
Best wishes,

Arno