Restoring CMS-DRL error / saturation

[Evelyne]

I collected a dataset with simultaneous EEG-tDCS measurements. Looking back, I should have placed the CMS/DRL electrodes at a different location, as I am currently experiencing some issues that I am trying to resolve. Based on this post: https://teams.public.onecdn.static.micr ... links.html

I would like to ask whether these datasets are still salvageable or if it would be better to throw them away.
The main issue is that I have several datasets showing partial or complete CMS/DRL signal loss, or behavior that looks like amplifier saturation. For quite some participants, I see for all electrodes periods of very high-voltage clipping. In some recordings, the CMS/DRL indicator lights were flickering during acquisition, while in others not and I only saw this issue during data . These problems occur only when the tDCS stimulator is active. The stimulation was 2 mA using a 4×1 HD-tDCS setup with the center electrode C3 and four return electrodes arranged in a ring around it. The system was a NeuroConn DC + stimulator.
The result is either fully clipped EEG signals or very large artifacts weird / negative in the psd, even before applying any preprocessing or cleaning steps.
Is there any way to recover or restore these signals?
So far, I have tried different referencing, + more automated processing pipelines, such as GEDAI, but without success.
Thank you for any advice or recommendations.

[Coen]

The location of the CMS/DRL does not affect the result after referencing.

Data with the Common Mode not in range (blue light blinking, bit 20 in the Status channel is LOW) are not valid and not recoverable.

Best regards, Coen

[Evelyne]

Dear Coen,

Thanks for your response.
Indeed, there were times when the blue light kept flickering, but in most cases this was not the case and the blue light was on.

However, when I look at the data, it appears to be a CMS-DRL-related issue. I either see unusual clipping artefacts or extremely large negative PSD values. Therefore, I do not think these observations are caused by the CMS-DRL itself flickering. Instead, my suspicion is that the CMS-DRL may be picking up interference from the tDCS signal and, as a result, all channels are affected. I cannot think of another explanation for why some participants show such abnormal PSD patterns. If you have any other suggestions or possible explanations, I would be very interested to hear them.