<div dir="ltr">Dear Michael,<div><br></div><div>Thank you for your comment.</div><div>I'm no authority of this issue, but generally speaking, if '<h2 id="gmail-:17j" class="gmail-hP" tabindex="-1" style="margin:0px;padding:0px 10px 0px 0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;font-size:inherit;line-height:inherit;font-family:inherit;display:inline;outline:none">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.</h2></div><div><h2 class="gmail-hP" tabindex="-1" style="margin:0px;padding:0px 10px 0px 0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;font-size:inherit;line-height:inherit;font-family:inherit;display:inline;outline:none"><br></h2></div><div><h2 class="gmail-hP" tabindex="-1" style="margin:0px;padding:0px 10px 0px 0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;font-size:inherit;line-height:inherit;font-family:inherit;display:inline;outline:none">I'm curious to see if motion artifact time-series correlates with accelerometer measurements recorded from the electrode.</h2></div><div><h2 class="gmail-hP" tabindex="-1" style="margin:0px;padding:0px 10px 0px 0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;font-size:inherit;line-height:inherit;font-family:inherit;display:inline;outline:none"><br></h2></div><div><h2 class="gmail-hP" tabindex="-1" style="margin:0px;padding:0px 10px 0px 0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;font-size:inherit;line-height:inherit;font-family:inherit;display:inline;outline:none">Makoto</h2></div><div><h2 class="gmail-hP" tabindex="-1" style="margin:0px;padding:0px 10px 0px 0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;font-size:inherit;line-height:inherit;font-family:inherit;display:inline;outline:none"><br></h2></div><div><h2 class="gmail-hP" tabindex="-1" style="margin:0px;padding:0px 10px 0px 0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;font-size:inherit;line-height:inherit;font-family:inherit;display:inline;outline:none"><br></h2></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, May 3, 2018 at 12:54 PM, Michael D. Nunez <span dir="ltr"><<a href="mailto:mdnunez1@uci.edu" target="_blank">mdnunez1@uci.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div>Thank you Makoto.<br><br></div>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.<br><br></div>Example references:<br><br><a href="https://www.researchgate.net/profile/Kristine_Snyder/publication/278792694_Isolating_gait-related_movement_artifacts_in_electroencephalography_during_human_walking/links/55873f3e08ae71f6ba914812.pdf" target="_blank">Isolating gait-related movement artifacts in electroencephalography during human walking</a><br><br><a href="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" target="_blank">Electroencephalography (EEG): Neurophysics, Experimental Methods, and Signal Processing</a><div><br><br></div></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Thu, May 3, 2018 at 12:20 PM, Makoto Miyakoshi <span dir="ltr"><<a href="mailto:mmiyakoshi@ucsd.edu" target="_blank">mmiyakoshi@ucsd.edu</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5"><div dir="ltr"><div>Dear colleagues,</div><div><br></div><div>Let me share this info.</div><div><br></div><div>E. Huigen (2000) Noise in biopotential recording using surface electrodes</div><div>
<span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><a href="https://www.semanticscholar.org/paper/Noise-in-biopotential-recording-using-surface-Huigen/8fc0837f7af0a36b19799139d9b763969057b985" target="_blank">https://www.semanticscholar.or<wbr>g/paper/Noise-in-biopotential-<wbr>recording-using-surface-<wbr>Huigen/8fc0837f7af0a36b1979913<wbr>9d9b763969057b985</a></span>
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<div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><b>%%%%%%%%%%%%%%%%%%%%%</b><br></div></div><div><b><br></b></div><div><b>2.4 Motion artifact</b></div><div>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.</div><div><br></div><div><b>Liquid junction potential variations by electrode movement</b></div><div>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 <span style="background-color:rgb(244,204,204)">400-600 μV</span> when the electrode is moved parallel to the skin surface <span style="background-color:rgb(207,226,243)">(Smith and Wace, 1995)</span>. When the electrode is moved perpendicular to the skin the potential changes can be up to <span style="background-color:rgb(244,204,204)">900 μV</span>. 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 <span style="background-color:rgb(244,204,204)">15 mV</span> 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).</div><div><br></div><div><b>Skin potential changes</b></div><div>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 <span style="background-color:rgb(244,204,204)">this skin potential is a liquid junction potential between deeper skin layers and the electrolyte.</span> 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</div><div>unwanted effects.</div><div><br></div><div>%%%%%%%%%%%%%%%%%%%%%</div><div><br></div><div>
<div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial">Wikipedia 'liquid junction potential'</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><a href="https://en.wikipedia.org/wiki/Liquid_junction_potential" target="_blank">https://en.wikipedia.org/wiki/<wbr>Liquid_junction_potential</a></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial">In Huigen, Peper, Grimbergen (2002) Med. biol. Eng, they described:</div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><br></div><i>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 <span style="background-color:rgb(244,204,204)">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).</span></i><br></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoration-style:initial;text-decoration-color:initial">By the way I could not find Smith and Wave (1995)<i><span> </span>European Journal of Anaesthesiology.<span> </span></i>If you have a copy, please let me know.</div><span class="m_1610435864102569510HOEnZb"><font color="#888888">
<br></font></span></div><span class="m_1610435864102569510HOEnZb"><font color="#888888"><div>Makoto</div>-- <br><div class="m_1610435864102569510m_-615631374590747166gmail_signature"><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div></div>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div></div>
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