[Eeglablist] [EXTERNAL] 16 Hz artifact with lower harmonics in data

[Malte Anders]

Hi Brian,

Every input here is very much appreciated, so please do not refrain from
giving very basic suggestions in case we missed something!

1) Something is also telling me that this is coming from the measuring
equipment itself. As you already suggested, this can be induced via the
grounding electrode. I need to get back in the lab next week and have a
very basic look. I was thinking of instrumentation as well, but have you
ever seen an externally induced artifact with an amplitude of 900
microvolts besides the 50/60 Hz artifact? I haven't... Even eye blinks are
200-300 microvolts max. But I will try to turn everything off anyways.
2 and 3: very good suggestions. We have connected a signal generator and
got a very clean signal on the online recording screen. But we set that
signal generator to 5V (the maximum our recorder can measure), so we
probably missed 900 microvolts of artifact if there would have been any. I
need to input some milli- or microvolts and see if the artifact persists -
in hindsight, 5 Volt was not a useful idea. So very good suggestion.

I will keep you updated. In the meantime, thank you very much!

Malte


Brian Harvey <brian.harvey at biogen.com> schrieb am Do., 31. März 2022, 18:32:

> OK, thanks for the background and clarification. Your application is novel
> to me so I am uncertain how much help I can be…
>
>
>
>    1. Your reference or ground may be adding this?  Vibrations or
>    instrumentation could be “inducing” the artifact
>    2. Have you tried a single electrode and reference in a saline bath to
>    troubleshoot your instrumentation?
>    3. Use a signal generator to input a known signal and test for
>    artifact?
>
>
>
> These are obvious troubleshooting steps so please forgive me if I am
> offering advice already known/attempted; essentially having a known signal
> and simplifying your instrumentation to barebones… then add back in one
> thing at a time can help to isolate the culprit.
>
>
>
> Brian
>
>
>
> *From:* Malte Anders <malteanders at gmail.com>
> *Sent:* Thursday, March 31, 2022 12:01 PM
> *To:* Brian Harvey <brian.harvey at biogen.com>
> *Cc:* EEGLAB List <eeglablist at sccn.ucsd.edu>
> *Subject:* Re: [EXTERNAL] [Eeglablist] 16 Hz artifact with lower
> harmonics in data
>
>
>
> Hi Brian, thanks for answering. Yes, I agree that the fft looks unusable.
> This is due to the fact that the EEG I've sent is an "EEG" of a not fully
> developed embryo where we would normally expect a flat line, except maybe
> some ZjQcmQRYFpfptBannerStart
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> Hi Brian, thanks for answering.
>
>
>
> Yes, I agree that the fft looks unusable. This is due to the fact that the
> EEG I've sent is an "EEG" of a not fully developed embryo where we would
> normally expect a flat line, except maybe some movement artifacts. In other
> words, this is just some electrodes in living tissue where the brain will
> be later on. That tissue should not produce 16 Hz amplitudes of 900
> microvolts.
>
>
>
> The eeg is recorded with a hardware bandpass between 0.1 - 100 Hz and
> refiltered in EEGLAB between 1-40 Hz. No further processing. Setting the
> hardware filter to 1 - 100 Hz with 50 Hz notch produces the same artifact
> on the online recording screen, so the raw data should be imported
> correctly.
>
>
>
> Thanks,
>
> Malte
>
>
>
> Brian Harvey <brian.harvey at biogen.com> schrieb am Do., 31. März 2022,
> 17:33:
>
> The FFT has an unusual 1/f characteristic. Question(s)
>
>
>
>    1. Awake or anesthetized (if so what anesthesia)
>    2. Did you perform any filtering, referencing, or resampling?
>    3. Have you looked at the raw data, plot the raw traces outside of
>    EEGlab
>
>
>
> Brian
>
>
>
> *From:* eeglablist <eeglablist-bounces at sccn.ucsd.edu> *On Behalf Of *Malte
> Anders
> *Sent:* Thursday, March 31, 2022 6:21 AM
> *To:* EEGLAB List <eeglablist at sccn.ucsd.edu>
> *Subject:* [EXTERNAL] [Eeglablist] 16 Hz artifact with lower harmonics in
> data
>
>
>
> Dear all, We are currently trying to record EEGs on the open brain of
> certain animals - so no "standard" human recordings. The gold electrodes
> are placed directly on the brain, without any conductive gel applied. We
> are encountering a strange ZjQcmQRYFpfptBannerStart
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> Dear all,
>
>
>
> We are currently trying to record EEGs on the open brain of certain animals
>
> - so no "standard" human recordings. The gold electrodes are placed
>
> directly on the brain, without any conductive gel applied.
>
>
>
> We are encountering a strange ~16 Hz artifact, with harmonics around ~10.x
>
> Hz and ~5.x Hz, see these images:
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__ibb.co_NKMcrf0&d=DwIBaQ&c=-35OiAkTchMrZOngvJPOeA&r=kB5f6DjXkuOQpM1bq5OFA9kKiQyNm1p6x6e36h3EglE&m=c88_VOjmnuVwvN-A41WN_LrcUXdxqhHwgozv6g_vBGXNTPB1AS0LrJkqDp8M8B44&s=E8I2mkOB0AmaOPUEUXwPZvKu-BkYWuzhow82gl11YCg&e=
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__ibb.co_Z8zkCpp&d=DwIBaQ&c=-35OiAkTchMrZOngvJPOeA&r=kB5f6DjXkuOQpM1bq5OFA9kKiQyNm1p6x6e36h3EglE&m=c88_VOjmnuVwvN-A41WN_LrcUXdxqhHwgozv6g_vBGXNTPB1AS0LrJkqDp8M8B44&s=haiZvyK3aT-jVpA4wpHVfjQQrPRs1O0cx88EnN9NitE&e=
>
>
>
> Anybody ever saw artifacts in these frequency ranges? I am trying to narrow
>
> down if those artifacts stem from our recording setup itself (maybe bad
>
> impedance between the brain and the measuring electrode?), or from any
>
> other external hardware in our recording setup.
>
>
>
> Any help is much appreciated!
>
> Malte
>
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