<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">
Dear Arno,
<div class=""><br class="">
</div>
<div class="">I think you are mixing up the sourcemodel and the volume conduction model. These are 2 separate things.</div>
<div class=""><br class="">
</div>
<div class="">The BEM is a volume conduction model, and describes the geometries at which the potential distributions are computed that are the consequence of the volume currents, due to the primary currents in the brain.</div>
<div class=""><br class="">
</div>
<div class="">The sourcemodel describes the set of positions at which an active dipole is assumed, and for which a ‘leadfield’ is computed (in the forward modelling step) / for which the source power is estimated (for the inverse modelling step). </div>
<div class=""><br class="">
</div>
<div class="">The distributed sourcemodel can be defined as a 3D grid (suboptimal), or as a 2D surface. The latter can be obtained for instance using Freesurfer, as per the</div>
<h2 id="construction-of-a-source-model-based-on-a-surface-description-of-the-cortical-sheet" style="box-sizing: border-box; margin-top: 1.2rem; margin-bottom: 0.5rem; font-weight: 500; line-height: 1.2; color: rgb(33, 37, 41);" class="">
<span style="font-size: 14px;" class=""><font face="Arial" class="">'Construction of a source model based on a surface description of the cortical sheet'</font></span></h2>
<div class=""><br class="">
</div>
<div class="">section of</div>
<div class=""><br class="">
</div>
<div class=""><a href="http://www.fieldtriptoolbox.org/tutorial/sourcemodel/" class="">http://www.fieldtriptoolbox.org/tutorial/sourcemodel/</a></div>
<div class=""><br class="">
</div>
<div class="">This piece of documentation describes how the ‘Subject01_sourcemodel_15684.mat’ has been generated.</div>
<div class=""><br class="">
</div>
<div class="">I hope this helps.</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>
<div class=""><br class="">
</div>
<div class=""><br class="">
<div>
<blockquote type="cite" class="">
<div class="">On 15 May 2019, at 23:24, Arnaud Delorme <<a href="mailto:arno@ucsd.edu" class="">arno@ucsd.edu</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
<div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
Dear all,</div>
<div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
<br class="">
</div>
<div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
I am trying to perform source reconstruction on a BEM mesh of EEG data</div>
<div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">
The page below describes how to localize source on a BEM mesh for MEG data using minimal norm estimate on the BEM mesh itself. This is what I would like to do but for EEG data.
<div class=""><br class="">
</div>
<div class=""><a href="http://www.fieldtriptoolbox.org/tutorial/minimumnormestimate/" class="">http://www.fieldtriptoolbox.org/tutorial/minimumnormestimate/</a></div>
<div class=""><br class="">
</div>
<div class="">This page describes how to compute a leadfield matrix for EEG </div>
<div class=""><br class="">
</div>
<div class=""><a href="http://www.fieldtriptoolbox.org/workshop/baci2017/forwardproblem/" class="">http://www.fieldtriptoolbox.org/workshop/baci2017/forwardproblem/</a></div>
<div class=""><br class="">
However, the leadfield matrix created for EEG is for a 3-D grid, that can then be projected on a 3-D MRI volume - so not the projection on BEM mesh I would like. I have not been able so far to generate a leadfield matrix for a BEM surface. Now the tutorial
page below in theory describes how to create one for MEG from a BEM mesh (section "Realistic single-shell model, using brain surface from segmented mri").</div>
<div class=""><br class="">
</div>
<div class=""><a href="http://www.fieldtriptoolbox.org/example/make_leadfields_using_different_headmodels/" class="">http://www.fieldtriptoolbox.org/example/make_leadfields_using_different_headmodels/</a></div>
<div class=""><br class="">
</div>
<div class="">However, again I obtained a 3-D source model on a grid. I figured that the sourcemodel needs to look like this (the content below is for tutorial MEG file named Subject01_sourcemodel_15684.mat). However, I do not know how this file was generated
and how it could be transposed for EEG (which needs 3 layers instead of 1 etc…).</div>
<div class=""><br class="">
</div>
<div class="">sourcemodel = <br class="">
<br class="">
struct with fields:<br class="">
<br class="">
pos: [15684×3 double]<br class="">
tri: [31360×3 double]<br class="">
sulc: [15684×1 double]<br class="">
curv: [15684×1 double]<br class="">
thickness: [15684×1 double]<br class="">
brainstructure: [15684×1 double]<br class="">
brainstructurelabel: {2×1 cell}<br class="">
inside: [15684×1 logical]</div>
<div class=""><br class="">
</div>
<div class="">Any hint would be appreciated.</div>
<div class="">Cheers,</div>
<div class=""><br class="">
</div>
<div class="">Arno</div>
</div>
</div>
_______________________________________________<br class="">
fieldtrip mailing list<br class="">
<a href="https://mailman.science.ru.nl/mailman/listinfo/fieldtrip" class="">https://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a><br class="">
https://doi.org/10.1371/journal.pcbi.1002202<br class="">
</div>
</blockquote>
</div>
<br class="">
</div>
</body>
</html>