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

[Brian Harvey]

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<mailto: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<mailto: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<mailto: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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