The flat, silver electrodes that our clinic used to use are no longer available so we ordered a new brand (Nicolet) for ear clips and individual electrodes. We had a lot of having issues with the ear clips working with the older electrodes so we swapped them all out for new, same-brand electrodes.
This helped, but we are having other issues now. During a session, an ear clip will “stop working” and the data is suddenly full of beta waves. When we replace the reference ear clip, the data goes back to normal. None of the ear clips are broken, they just don’t seem to be referencing correctly. Has anyone else ran into this problem, where the references aren’t working properly and instead of the EEG line becomming really flat (like I have seen other times when ear clips/references stop working), there are excess beta waves? Im not sure if we need new ear clips or if it could be an issue with the amplifier?
re: flat vs cups
My impression is that practitioners like the cups because these have higher surface area than the flats and thus have increased adhesion with the paste.
re: intermittent reference
I assume your new electrodes are solid silver cups? Any type of ‘plated’ electrodes (such as gold over tin) are risky because if a chip ever occurs, a galvanic battery is formed and will introduce a large DC artifact.
Obviously you want to use all the same metal type throughout, as mixing metals can also result in galvanic effects. Even with solid silver or solid tin, oxidation can happen at the surface over time, so your cleaning technique needs to avoid this. Silver is the main culprit. Tin not so much.
When cleaning paste from the electrodes, the most common recommendation is to dip the electrode metal end ONLY, into very hot almost boiling water. The paste will then fall off naturally. Never (by mistake) insert the electrode so far that the electrode-wire junction contacts the water. That could cause unknown / unstable corrosion in the wire connection joint.
re: beta waves
I doubt this is an issue with your amp. An unstable electrode-wire junction could increase impedance substantially and allow room ambient EMF fields (such as 60 Hz and sub harmonics) to be induced. If you have a failing reference, use a DVM meter to check that it is close to zero ohms from electrode to the touchproof connector.
re: disposables
Disposable silver chloride cups (and clips) are becoming more common. These are plastic base material, plated with silver metal and then chlorided. Silver chloride is the highest stability of any electrode material.
William
Thank you so much for this response! I think the ambient EMF fields part makes a lot of sense, it also sounds like we just need new ear clips. This info is VERY much appreciated!
@wjcroft Hello, I have a quick follow-up question; Can you mix the Silver cups (ear clips) with flat Silver individual electrodes?
Yes, using the same metal (Silver) in your case, regardless of form (cups or flat), is fine because there is no galvanic battery effect. An example of improper mixing would be the silver with tin or silver with gold or gold with tin, etc.
My impression is that silver chloride may be an exception, because the chloride surface is not technically a ‘metal’. But underneath the chloride layer is a silver plate. So if the chloride were to chip or wear off, you would have the same situation with silver.