Does anyone have experience with iEEG recordings? One of our projects tried to record iEEG with an ANT Neuro amplifier and touch-proof connectors. The ANT Neuro amplifiers are designed to record ānormalā EEG with either dry, gel-base, or sponge-base caps from 32 to 256 channels. With the touch-proof connectors, we can record from any kind of cap/electrodes, in this case from intracranial electrodes.
Both the GND and the reference are 2 intracranial electrodes, similar to the others. The signal had a massive drift, going up 80 mV in a couple of minutes (and clipping to the boundaries of the amplifier measurement range 150 mV).
Is this drift something ānormalā when recording with intracranial electrodes? Any idea how we could reduce it without hardware filters (which the ANT amplifier does not have as itās not really designed for iEEGā¦)?
We can connect additional electrodes on AUX channels, and we can connect an additional GND if needed (I have no clue what the impact would be).
Any tips and feedback from iEEG users would be welcome, thank you!
Hmmm, I have experience with intracranial recordings but typically the setup done by a hospital and not primarily driven by research purposes so I would guess that using not-as-the-manufacturer-specified would be pretty rare. That being said, signal drift is ubiquitous in all kinds of electrophysiology recordings but is usually compensated for in the hardware. The things you could try are moving the ground, trying to lower the impedance on the reference or changing the referencing scheme in the hardware. Iām guessing youāve tried those kinds of things but maybe changing the recordings settings in regards to the reference is something that might be worth a try.
The thing is, we were not present when they did the recordings at the hospital, and something went wrong and we have no idea what + we are very inexperienced in iEEG.
I will suggest they try connecting different electrodes to the GND and REF lead and see what comes out of it.
Those amplifiers work fine with ānormalā EEG caps, with a large DC offset, but a very small drift. Do you think it might be that the DC drift measured by intracranial electrodes is way stronger/different than the one measured with ānormalā EEG caps, and thus is badly compensated for by the hardware that is not designed to handle it?
Iām still surprised that the drift would be so different between intracranial electrodes and scalp ānormalā electrodes. I canāt find a reason why this would be the case.
Yeah, Iām not sure about what the extra source of drift would be intracranially. Unfortunately, I think this sort of thing is terribly hard to troubleshoot remotely and really involves someone with a bit of experience and a good amount of common sense taking a look around and thinking things through in person. Sorry, thatās not much help!
Also, engineers at ANT Neuro might have some advice, the amplifier designs are actually quite a bit different as Iāve discovered (not really my field but Iāve had issues with a photodiode deflecting too sharply which is the opposite issue which was caused when the manufacturer changed from a DC to an AC differential amplifier).
Thank you, I agree someone knowledgeable on-site is a necessity to troubleshoot this (and I hope this will be the case next time). Iām not even sure about what they tried and what they did notā¦
We are contacting ANT in parallel. So in your experience, the design of the ANT amplifiers changed? Iām curious because we have 2 that are 7 years old, and 2 that are very recent.
Iām not sure about what the extra source of drift would be intracranially.
Me neitherā¦ thatās the aspect that eludes me and that I hoped someone might explain
I donāt have any solid input or experience with ANT but I thought Iād share my thoughts on this. I regularly work with ieeg and that kind of signal drift is very unusual. We record using both the clinical system amplifier and an amplifier from Tucker-Davis Technologies (TDT) for better signal quality. However, the TDT amplifier is usually the one that will produce some error in the signal if there is any. The clinical system usually records at a lower sampling rate but is usually more reliable. When we experience some signal error itās usually due to hardware. Whenever an ieeg recording is done someone should always be monitoring the signal on the amplifier being used. Both because something can go wrong with the signal and your neural data becomes worthless and because, if these are people with seizures, thereās a chance for some abnormal activity. Best way to tell is to look at the clinical system signal and the ANT amplifier signal simultaneously. If your ANT signal is drifting but not the clinical system, you know itās probably something wrong with the ANT hardware. Sometimes what my lab does is record from the clinical amplifier and TDT amplifier simultaneously by sending TTL pulses, or some kind of burst to sync them, to both amplifiers. If the TDT, or your case ANT, amplifier produces an odd signal, youāll still have the clinical system signal.
That being said, you can try something like creating a bipolar reference of the data and see if that makes the data look any better. Hope this helps.
One more piece of information: someone pointed out that iEEG electrodes are usually made out of steel/platinum while caps electrodes are Silver/Silver Chloride electrodes. Both are not subject to the same drift (battery effect?), but eventually, after a period of time, the drift should settle.
