Dear List,<div><br></div><div>I was under the impression that positive deflections reflect dipoles moving toward an electrode and negative deflections reflect dipoles moving away from an electrode. I would be interested in seeing the evidence correlating negative potentials with cortical activation and positive potentials with cortical inhibition.</div>
<div><br></div><div>Cheers,</div><div>Teresa Hawkes</div><div>University of Oregon<br><br><div class="gmail_quote">On Thu, Jun 16, 2011 at 6:55 PM, Geert van Boxtel <span dir="ltr"><<a href="mailto:G.J.M.vBoxtel@uvt.nl">G.J.M.vBoxtel@uvt.nl</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><u></u>
<div text="#000000" bgcolor="#ffffff">
Dear list,<br>
<br>
The historical "accidents" that Steve describes actually had a sound
basis in neurophysiology in that negativity measured at the scalp
was supposed to reflect cortical activation, whereas positivity
measured at the scalp was thought to reflect cortical inhibition,
both at the level of postsynaptic potentials (EPSPs and IPSPs,
respectively). Much research in the 1960s focused on three types of
ERPs: the negative Contingent Negative Variation (CNV) and Readiness
Potential (RP), and the positive P300. For the CNV and RP, an
increase in negativity meant an increase in cortical activity, so it
made perfect sense to plot these potentials negative-up.<br>
<br>
Nowadays, the convention originating from physics to plot positivity
upwards is becoming more and more current. Of course, polarity
depends on the reference used in the recording, so it should be
considered good science to be able to think both negative-up and
positive-up.<br>
<br>
Best regards,<br>
Geert<br>
<br>
<br>
<br>
Op 16-6-2011 21:42, Steve Luck schreef:
<blockquote type="cite"><div><div></div><div class="h5">
<div>Mehmet-</div>
<div><br>
</div>
<div>The polarity conventions in ERP research are arbitrary and
partially reflect historical accidents. You can plot negative
upward if you mainly want to communicate your results to people
who are used to looking at ERPs with negative upward. You
should plot positive upward if you mainly want to communicate
your results to the 99.999999% of scientists who use the
Cartesian convention of plotting positive upward.</div>
<div><br>
</div>
<div>Steve</div>
<div><br>
</div>
<div><br>
<blockquote type="cite"><br>
<div style="margin:0px"><span style="font-family:'Helvetica';font-size:medium;color:rgb(127, 127, 127)"><b>From: </b></span><span style="font-family:'Helvetica';font-size:medium">mehmet ali <<a href="mailto:theretinaguy@gmail.com" target="_blank">theretinaguy@gmail.com</a>><br>
</span></div>
<div style="margin:0px"><span style="font-family:'Helvetica';font-size:medium;color:rgb(127, 127, 127)"><b>Date: </b></span><span style="font-family:'Helvetica';font-size:medium">June 16, 2011 5:29:38 AM
PDT<br>
</span></div>
<div style="margin:0px"><span style="font-family:'Helvetica';font-size:medium;color:rgb(127, 127, 127)"><b>To: </b></span><span style="font-family:'Helvetica';font-size:medium"><a href="mailto:eeglablist@sccn.ucsd.edu" target="_blank">eeglablist@sccn.ucsd.edu</a><br>
</span></div>
<div style="margin:0px"><span style="font-family:'Helvetica';font-size:medium;color:rgb(127, 127, 127)"><b>Subject: </b></span><span style="font-family:'Helvetica';font-size:medium"><b>[Eeglablist] p300
convention</b><br>
</span></div>
<br>
<br>
Hi all,<br>
<br>
p300 is conventionally plotted on an inverted axis( positive
potentials to down), is there a reason to end up with this
convention?<br>
<br>
Best,<br>
<br>
<br>
<br>
<br>
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Ph.D. Candidate<br>Department of Human Physiology<br>University of Oregon<br>348 Gerlinger Hall,<br>1240 University of Oregon<br>Eugene, Oregon 97403-1240<br>Phone: 541-337-9443 (cell) or 541-346-0275 (laboratory)<br><a href="mailto:thawkes@uoregon.edu" target="_blank">thawkes@uoregon.edu</a><br>
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