<div dir="ltr">Dear Ahmed,<br><br>> My question is, why the dipoles distribution is symmetric over the scalp? <br><br>I'm not an expert of this field, but the answer to 'why dipole?' should be found in electromagnetics. I hope someone who knows this topic help us here.<br><br>> According to my understanding there is an infinite number of dipoles may contribute in a specific source. Is there any justification (Please correct me if I’m wrong)?<br><br>In order for scalp channel to observe meaningful EEG, certain amount of neurons that are aligned and activating together are necessary. That's like a prerequisite for EEG measurement.<br><br>>Also why the volume conduction effect (transmission of electric current from primary source electrode to other electrodes) can be seen in some experiments only while it’s much less in some other experiment?<br><br>That's wrong. It's always there.<br><br>> What's the experimental factors may effect on volume conduction?<br><br><div>It must be very very very stable and can be hardly affected by any experimental factors.</div><div><br></div><div>Makoto<br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Dec 3, 2014 at 2:14 AM, Ahmed Almurshedi <span dir="ltr"><<a href="mailto:ahmed19875000@yahoo.com" target="_blank">ahmed19875000@yahoo.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="color:rgb(0,0,0);font-family:HelveticaNeue,'Helvetica Neue',Helvetica,Arial,'Lucida Grande',sans-serif;font-size:16px;background-color:rgb(255,255,255)">
<div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif">Dear
Experts,</span></div><div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif"><br></span></div>
<div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif">I
have noticed in some ERP experiments that the response is flipped in the
posterior part than anterior part of scalp. For example in checkerboard pattern
VEP, P100 response on mid occipital electrode and N100 response on the frontal
electrode.</span></div>
<div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif">According
to the discussion with colleagues they said that ERP response are usually from
the generation of a dipole, the field of which is picked up at different
electrode locations.<span> </span>Thus, some will
pick up the positive end, and others will pick up the negative end. This is
often called phase reversal, as the phase of waveform is 180 degrees reversed.</span></div><div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif"><br></span></div>
<div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif">My
question is, why the dipoles distribution is symmetric over the scalp?
According to my understanding there is an infinite number of dipoles may
contribute in a specific source.<span> </span>Is
there any justification (Please correct me if I’m wrong)?</span></div><div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif"><br></span></div>
<div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif">Also
why the volume conduction effect (transmission of electric current from primary
source electrode to other electrodes) can be seen in some experiments only
while it’s much less in some other experiment? What's the experimental factors
may effect on volume conduction?</span></div><div><br>
</div><div><div dir="ltr"></div><div dir="ltr">
</div><div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif">Thank you,</span></div><div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif"><br></span></div>
<div style="text-align:justify"><span style="font-size:12pt;line-height:115%;font-family:'Times New Roman',serif">AHMED</span></div>
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For digest mode, send an email with the subject "set digest mime" to <a href="mailto:eeglablist-request@sccn.ucsd.edu">eeglablist-request@sccn.ucsd.edu</a><br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="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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