[Eeglablist] Movement artifact = Liquid junction potential

Thu May 3 14:22:05 PDT 2018

Dear Michael,

Thank you for your comment.
I'm no authority of this issue, but generally speaking, if 'Movement
artifact = Liquid junction potential', motion artifact reflects the amount
of displacement of the electrode against contacting body of fluid. This
seems the movement artifact represents the first order derivative of the
amount of the electrode displacement. Slow motion artifact could be
generated by a slow motion, and sudden potential difference spikes could be
generated by sudden, jerky motion.

I'm curious to see if motion artifact time-series correlates with
accelerometer measurements recorded from the electrode.

Makoto

On Thu, May 3, 2018 at 12:54 PM, Michael D. Nunez <mdnunez1 at uci.edu> wrote:

> Thank you Makoto.
>
> In EEG recordings do we expect movement artifact (due to liquid junction
> potential) to be expressed at slow frequencies or sudden potential
> difference spikes (i.e. temporary electrical discontinuities)? I have found
> empirical evidence of both.
>
> Example references:
>
> Isolating gait-related movement artifacts in electroencephalography during
> human walking
> <https://www.researchgate.net/profile/Kristine_Snyder/publication/278792694_Isolating_gait-related_movement_artifacts_in_electroencephalography_during_human_walking/links/55873f3e08ae71f6ba914812.pdf>
>
> Electroencephalography (EEG): Neurophysics, Experimental Methods, and
> Signal Processing
> <https://www.researchgate.net/profile/Michael_Nunez4/publication/290449135_Electroencephalography_EEG_neurophysics_experimental_methods_and_signal_processing/links/57bf32c908ae2f5eb32e82a9/Electroencephalography-EEG-neurophysics-experimental-methods-and-signal-processing.pdf>
>
>
>
> On Thu, May 3, 2018 at 12:20 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:
>
>> Dear colleagues,
>>
>> Let me share this info.
>>
>> E. Huigen (2000) Noise in biopotential recording using surface electrodes
>> https://www.semanticscholar.org/paper/Noise-in-biopotential-
>> recording-using-surface-Huigen/8fc0837f7af0a36b19799139d9b763969057b985
>>
>> *%%%%%%%%%%%%%%%%%%%%%*
>>
>> *2.4 Motion artifact*
>> Movement can cause changes in the potentials that are created when an
>> electrode is applied to the skin. Normally, when the patient is relaxed,
>> and high quality electrodes are used, the recording is not distorted by
>> motion artifact. Brinkman (1993) has found no significant correlation
>> between the intentional movement of the arm and the noise signal. The
>> mechanisms that can cause motion artifact are described next.
>>
>> *Liquid junction potential variations by electrode movement*
>> The various phase junctions in the electrode-electrolyte-skin interface
>> all cause junction potentials, sensitive to motion artifact. The
>> skin-electrolyte interface can cause artifacts of 400-600 μV when the
>> electrode is moved parallel to the skin surface (Smith and Wace, 1995).
>> When the electrode is moved perpendicular to the skin the potential changes
>> can be up to 900 μV. Firm attachment to the skin can reduce the
>> potential changes. The electrode-electrolyte interface also produces
>> artifacts when mechanically disturbed. Gatzke (1974, as described in
>> Webster, 1984) measured a 15 mV potential change when a pure silver
>> electrode is moved in electrolyte. Coating with silver chloride, thus
>> creating a stable double layer, produces a 10-fold reduction of the
>> artifact. Further reduction (up to negligible value) can be achieved by
>> recessing the electrode-electrolyte interface in a protective cup, in which
>> a sponge soaked in gel is placed (figure 2-2).
>>
>> *Skin potential changes*
>> Earlier, the stratum corneum and the barrier layer have been identified
>> as the major sources of the impedance of the skin. Webster (1984) has also
>> observed a potential difference between the inside and the outside of the
>> barrier layer. Van Wijk van Brievingh (1988) however states that this
>> skin potential is a liquid junction potential between deeper skin layers
>> and the electrolyte. The skin potential has a typical value of 30 mV at
>> the thorax. Stretching of the skin decreases the skin potential to about 25
>> mV. This artifact can be reduced to negligible value by abrading the skin.
>> Webster gives 20 strokes with fine sandpaper as an indication. Shackel
>> (1959, as described in Geddes and Baker, 1989) developed a method for
>> shorting the skin potential, called the skin-drilling technique. The
>> epidermis is eroded using a dental burr. The capillaries remain
>> undisturbed, so no blood is drawn. Unfortunately, the epidermis is also the
>> layer that protects the skin from irritation. A mild electrode gel has to
>> be used to prevent
>> unwanted effects.
>>
>> %%%%%%%%%%%%%%%%%%%%%
>>
>> Wikipedia 'liquid junction potential'
>> https://en.wikipedia.org/wiki/Liquid_junction_potential
>>
>> In Huigen, Peper, Grimbergen (2002) Med. biol. Eng, they described:
>>
>> *RECORDINGS  OF  biomedical  signals  from  the  body  surface  often
>>  contain  a  substantial  noise  component. This  noise  signal  can
>>  severely  impair  the  resolution  of  biomedical  recordings  as  its
>>  magnitude  can  be  as high  as  10-60  uVp_p  (GONDRAN  et  aL,  1996).
>> This  is  in  the  range  of  EEG  potentials  and  is  at  least ten
>>  times  as  high  as  several  types  of  evoked  potentials  (e.g.  visual
>>  evoked  potentials  or  somatosensory evoked  potentials).*
>>
>> By the way I could not find Smith and Wave (1995)* European Journal of
>> Anaesthesiology. *If you have a copy, please let me know.
>>
>> Makoto
>> --
>> Makoto Miyakoshi
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
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>
>
>
> --
> Michael D. Nunez
> Associate Specialist (Neuroscientist)
> Laboratory of Computational and Translational Neuroscience
> <http://lopour.eng.uci.edu/>
> Dept. of Biomedical Engineering
> Human Neuroscience Lab <http://hnl.ss.uci.edu>
> Cognition and Individual Differences Lab <http://www.cidlab.com/>
> Dept. of Cognitive Sciences
> University of California, Irvine
>

-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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