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<p>Dear Fabio,</p>
<p>when you switch from anodal to cathodal stimulation with
otherwise identical settings, you only change the direction of the
currents. Everything else stays the same. For example, the
electric field strength will not be affected by that.</p>
<p>To see the changes, you can look at the "E" instead of "normE"
(the former are the field vectors; the latter is the field
strength, i.e. the length of the vectors). E will change the
direction. Another way to look at the changes is to visualize the
component of the field that flows in or out of the cortex. This
component is usually termed "normal component"
(<a class="moz-txt-link-freetext" href="https://simnibs.github.io/simnibs/build/html/faq.html">https://simnibs.github.io/simnibs/build/html/faq.html</a>).</p>
<p>You can get the normal component when you enable "Interpolate to
cortical surface" in the simulation options
(<a class="moz-txt-link-freetext" href="https://simnibs.github.io/simnibs/build/html/tutorial/gui.html">https://simnibs.github.io/simnibs/build/html/tutorial/gui.html</a>).
It then looks similar to Fig 11A in this paper:
<a class="moz-txt-link-freetext" href="https://www.biorxiv.org/content/10.1101/500314v1">https://www.biorxiv.org/content/10.1101/500314v1</a><br>
</p>
<p>Best regards,</p>
<p>Axel<br>
</p>
<div class="moz-cite-prefix">On 12/19/2020 1:29 PM, Fabio Masina
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAPJmCpFota1acjCr69Jp5yO5a-EvQw==MaGgFXtaU==+dw5ZKA@mail.gmail.com">
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<div>Dear colleagues,</div>
<div><br>
</div>
I tried to perform two tDCS simulations (both setting 2mA) using
the default head model (i.e., Ernie). The electrode positions
were:<br>
<br>
1st simulation_anodal tDCS (target electrode on F7, return on
FP2)<br>
<div>2nd simulation_cathodal tDCS (target electrode on F7,
return on FP2)</div>
<div><br>
</div>
Basically, I only changed the current direction, by changing the
polarity of the target electrode accordingly to the kind of
stimulation (2mA for anodal tDCS and -2mA for cathodal tDCS).<br>
<div>After launching these simulations separately, I realized
that the outputs were exactly the same. Actually, I would have
expected to view two oppositive outputs. I mean, I would have
expected two opposite e-field patterns. Maybe, am I missing
something?<br>
</div>
<br>
Thanks for any suggestion.<br>
<br>
Best.<br>
<br>
Fabio
<div>
<div>-- <br>
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<div
style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><b>Fabio
Masina, PhD<br>
</b></div>
<span><br>
</span>IRCCS, Ospedale San Camillo<br>
Via Alberoni 70, <span>30126 <br>
Venice, Italy</span></div>
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<pre class="moz-signature" cols="72">--
Dr. Axel Thielscher
Associate Professor
Danish Research Center for Magnetic Resonance
Copenhagen University Hospital Hvidovre
DK-2650 Hvidovre, Denmark
<a class="moz-txt-link-abbreviated" href="http://www.drcmr.dk">www.drcmr.dk</a>
&
Department of Health Technology
Technical University of Denmark
DK-2800 Kgs. Lyngby
<a class="moz-txt-link-freetext" href="http://www.healthtech.dtu.dk/">http://www.healthtech.dtu.dk/</a></pre>
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