Pronounced Occipital-Dominant Activity in Brain Products EEG Recordings

Discussions
1

Hi everyone,
We have been seeing a strange and persistent pattern in our EEG recordings and would like to hear if anyone has experienced something similar.

Setup:

  • Brain Products actiCAP + BrainAmp amplifier

  • Multiple cap sizes, matched to head size & sex

  • Participants: asian adults (Both Healthy and disease model)

  • Low impedances, controlled environment Previous system (Grass/Natus + Waveguard Cap, ANT)

  • resting EEG (eye-closed)
    did not show this issue Problem Across all participants and experiments, we observe occipital-dominant activity in the topography, regardless of frequency bands.
    It appears consistently even with different caps, operators, and recording days.

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(an example of a patient, but healthy participants also showed same patterns)

While similar occipital activity can be seen in the high-frequency range with our previous Grass system, it is far less pronounced compared to the Brain Products recordings.

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(Grass system, a patient case in the same cohort)

What we’ve checked Environmental artifacts → unlikely (appears in all subjects)
Alpha–beta misclassification → no change in alpha topography when redefined
Population-specific head shape → possible, but Waveguard data from same population was normal
Multiple preprocessing pipelines → same result

I’d like to know: Has anyone observed a similar occipital-dominant pattern with Brain Products systems? Any insights on possible causes (hardware, grounding, reference) or troubleshooting steps would be greatly appreciated.

Thanks,
Tae-Gon

2

I remember that when I was working at university lab, our ERP recordings made with BrainAmp tended to show the max voltage in occipital leads, tough our paradigm was for catching frontal activity.

As far as I know, BrainAmp uses an active central reference, making hard to clean the EEGs even with re-referencing

However, I think in your case (and in the previous above) it is probably an artifact

3

Thank you for your reply.
We initially considered the possibility of an artifact as well, but found no issues with the environment or recording settings.

Moreover, the same phenomenon was observed consistently across more than 100 datasets, making it unlikely that a common artifact was responsible.

May I ask what you concluded was the cause of the occipital leads’ maximum voltage in your previous case?

4

In our case we concluded it was due to the amplifier (BrainAmp)

5

Make sure the reference electrode is properly specified or re-reference the data with respect to the mean across electrodes.

6

Thank you for your helpful comments. While I did not mention it in the previous message, AFz was used as the reference channel. The same patterns remain even after re-referencing to the average across electrodes.

Additionally, we verified that the electrodes were functioning properly by performing a saline test.