channel positions missing after setting montage

šŸ’¬ Support & Discussions
1
  • MNE version: 1.6.0
  • operating system: Google Colab
    My dataset(bcic iv 2a) have 22 EEG channel and 3 EOG channels. The channel names are EEG-Fz, EEG-0, EEG-1, EEG-2, EEG-3, EEG-4, EEG-5, EEG-C3, EEG-6, EEG-Cz, EEG-7, EEG-C4, EEG-8, EEG-9, EEG-10, EEG-11, EEG-12, EEG-13, EEG-14, EEG-Pz, EEG-15, EEG-16, EOG-left, EOG-central, EOG-right.
    I tried to set montage using this:
raw.set_channel_types({'EOG-left':'eog','EOG-central':'eog','EOG-right':'eog'})
montage = mne.channels.make_standard_montage('standard_1020')
raw.set_montage(montage,on_missing='ignore')

But if I run raw.info['dig'] , it only shows LPA, Nasion and RPA and no channel positions.
Also, if I run raw.plot_sensors() , an error is being shown (RuntimeError: No valid channel positions found).
How to set the montage correctly?

2

Your data contains non-standard electrode labels. Before assigning a montage with raw.set_montage(), you need to rename your channels to standard 10ā€“20 labels (e.g. C3, Cz, C4, ā€¦). You can do this with raw.rename_channels().

2 Likes
3

Now I renamed the 5 channels whose corresponding standard 1020 channels I could understand.

map = {'EEG-Fz':'Fz', 'EEG-C3':'C3','EEG-Cz':'Cz','EEG-C4':'C4','EEG-Pz':'Pz'}
raw.rename_channels(mapping=map)

I could not understand if other channels are custom electrodes or else (dataset description mentions interelectrode distance of 3.5 cm). Do I have to calculate their co-ordinates from the co-ordinates of these five electrodes?
montage2
montage

4

It looks like these electrodes are placed according to the extended 10ā€“20 system (sometimes referred to as 10ā€“10), so Iā€™d also rename these accordingly (see e.g. 10ā€“20 system (EEG) - Wikipedia).

2 Likes