[This is no longer accurate, see next post below.]
I’m happy to say that the disposable electrodes I purchased as a trial a while back have lasted much longer than I initially expected. So we’ll keep using those for our usual EOG/ECG setup. I just added 2 new bundles with the same color code as last time:
for ECG/VEOG/HEOG respectively.
Green is always ground.
Sadly, the last batch of disposable electrodes I purchased (same brand) are much worse quality and only lasted a few uses before starting breaking. So I don’t recommend using those anymore. Instead, I made a bundle with others we had which are good quality reusable gold cup electrodes (tarnished but still work fine). They are kept on the left of the electrode rack, with grey connectors.
The electrodes we’ve been using lately, Grass gold-plated cup electrodes, are very slightly magnetic. This was confirmed recently and explains the very small low-frequency artefact we regularly saw in the MEG channels around the top VEOG electrode, associated with head movements. While the artefact is very small, it’s still best to avoid it completely by using instead the disposable electrodes hanging on the right side of the hooks on the wall.
I will look for a better alternative since these are now poor quality and break easily. In the meantime, don’t hesitate to swap electrodes when one doesn’t seem to work (impedance meter shows “1___”). Please set the “bad” ones aside for me to test, or put them in the garbage if they’re broken.
Note: this is not related to the EEG system issue also posted today, though both can affect the same MEG channels close to the electrodes. The artefact here is related to movement and very low frequency, whereas the other one is high frequency, from the electronics.
