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<p>Hi all,</p>
<p><br>
</p>
<p>I do not remember how mutual information is computed but maybe this is still informative:</p>
<p><br>
</p>
<p>Maybe the simplest form of signal similarity is correlation. Beamformer, in theoretical conditions i.e. as described in van Veen 1997 and the Sekihara--Nagarajan book, does not see correlated activity. So if our signal is produced by two sources whose time-courses
are partially correlated, and we have a perfect measurement of the signal, the LCMV estimate shows only those parts of the two source time-series that are uncorrelated with the other source. In real world, noise, regularization, model errors, under-determination
(more true sources than degrees-of-freedom in the measurement) etc. enter the game, but the theoretical property is still buried there. <br>
</p>
<p><br>
</p>
<p>So I am not surprised that LCMV estimate does not reproduce an MI effect.</p>
<p><br>
</p>
<p>Cheers,<br>
</p>
<p> Matti<br>
</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Lähettäjä:</b> fieldtrip <fieldtrip-bounces@science.ru.nl> käyttäjän Schoffelen, J.M. (Jan Mathijs) <jan.schoffelen@donders.ru.nl> puolesta<br>
<b>Lähetetty:</b> 28. tammikuuta 2021 14:49:21<br>
<b>Vastaanottaja:</b> FieldTrip discussion list<br>
<b>Aihe:</b> Re: [FieldTrip] mutual information on LCMV virtual channels</font>
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<div>Hi Xavier,
<div class=""><br class="">
</div>
<div class="">It’s not clear what in a resting-state context is meant with ‘baseline’. Neither what is meant with an increase in mutual information in the frontal region. Typically, mutual information is computed between 2 things, so what’s the other thing?</div>
<div class=""><br class="">
</div>
<div class="">Yet, regarding the question relating to source vs. electrode space: mutual information is not immune for volume conduction effects, so what you observe at the channel level might reflect a difference in power, rather than a difference in connectivity.
(Partially) undoing the volume conduction through source reconstruction might result in a reduction in the signal leakage, and hence a reduction in the MI. </div>
<div class=""><br class="">
</div>
<div class="">Best wishes,</div>
<div class="">Jan-Mathijs</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
<div><br class="">
<blockquote type="cite" class="">
<div class="">On 25 Jan 2021, at 08:39, Schoffelen, J.M. (Jan Mathijs) <<a href="mailto:jan.schoffelen@donders.ru.nl" class="">jan.schoffelen@donders.ru.nl</a>> wrote:</div>
<br class="Apple-interchange-newline">
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Hi Xavier,
<div class=""><br class="">
</div>
<div class="">I am forwarding your question to the list, this is a better venue to ask your question. More people can chime in and think along.</div>
<div class=""><br class="">
</div>
<div class="">I am aware that this question has been asked before on the list, and apparently it has not been answered. Perhaps now there is somebody who has time to think along.</div>
<div class=""><br class="">
</div>
<div class="">Best wishes,</div>
<div class="">Jan-Mathijs</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
<div class="">
<blockquote type="cite" class="">
<div class="">Begin forwarded message:</div>
<br class="Apple-interchange-newline">
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<span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif;" class=""><b class="">From:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">Xavier Vrijdag <<a href="mailto:x.vrijdag@auckland.ac.nz" class="">x.vrijdag@auckland.ac.nz</a>><br class="">
</span></div>
<div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;" class="">
<span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif;" class=""><b class="">Subject:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class=""><b class="">mutual information on LCMV virtual channels</b><br class="">
</span></div>
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<span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif;" class=""><b class="">Date:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">25 January 2021 at 02:48:06 CET<br class="">
</span></div>
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<span style="font-family: -webkit-system-font, "Helvetica Neue", Helvetica, sans-serif;" class=""><b class="">To:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;" class="">"<a href="mailto:jan.schoffelen@donders.ru.nl" class="">jan.schoffelen@donders.ru.nl</a>" <<a href="mailto:jan.schoffelen@donders.ru.nl" class="">jan.schoffelen@donders.ru.nl</a>><br class="">
</span></div>
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<span lang="EN-US" class="">Hello Jan-Mathijs,<o:p class=""></o:p></span></div>
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<span lang="EN-US" class=""><o:p class=""> </o:p></span></div>
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<span lang="EN-US" class="">I am using the mutual information analysis from the IBTB toolbox as incorporated in fieldtrip to run connectivity analysis on resting-state EEG data (32 channels) of participants exposed to narcotic gases. I found an increase in
mutual information in the frontal region compared to baseline. I am interested in localizing this effect further, so I set up an LCMV beamformer source localization. However, in the derived time series of the virtual channels, the mutual information effect
is completely gone. Could someone help me explain this effect? Could it be that LCMV, in its attempt to calculate the spatial filters, cancels out the mutual information in the EEG signals?<o:p class=""></o:p></span></div>
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<span lang="EN-US" class=""><o:p class=""> </o:p></span></div>
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<span lang="EN-US" class="">If helpful, I can share the Matlab scripts of the analysis pipeline.<o:p class=""></o:p></span></div>
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<span lang="EN-US" class=""><o:p class=""> </o:p></span></div>
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<span lang="NL" class="">Regards,<o:p class=""></o:p></span></div>
<div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<span lang="NL" class=""><br class="">
Xavier Vrijdag<o:p class=""></o:p></span></div>
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<span lang="NL" class=""><o:p class=""> </o:p></span></div>
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<span lang="NL" style="font-size: 10pt; color: rgb(118, 113, 113);" class="">Xavier Vrijdag, MSc<o:p class=""></o:p></span></div>
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