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<p class="MsoNormal"><span lang="EN-US">Dear FieldTrip list,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I am trying to do a functional connectivity analysis using the power envelope correlation introduced by Hipp et al. (Nat Neuroscience 2012) as implemented in the ft_connectivity_powcorr_ortho function. My data consists
of 5 minutes of eyes-closed resting-state data and my schematic pipeline is as follows:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-US">I use LCMV beamforming to source reconstruct my bandpassed and preprocessed data<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-US">Using the resulting spatial filter I get a projected time series for every voxel (virtual channel)<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-US">I do a frequency analysis on these time series<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-US">The results of this frequency analysis (the Fourier coefficients) are used for the connectivity analysis using powcorr_ortho<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">To check the results of this analysis, I plotted the results of a seed-based connectivity analysis with a voxel in the left visual cortex (-20, -80, 20) as seed. In the alpha band, I expect to see a strong local connectivity
pattern in the occipital region extending partially into the contralateral hemisphere, similar to what Siems et al. NeuroImage 2016 find. However, I get a basically random connectivity pattern. When using this pipeline with the debiased weighted phase lag
index, I get exactly what I am expecting.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I looked into the source code of the ft_connectivity_powcorr_ortho function and saw a few disconcerting comments (Fix-Me’s and the like) and now I am wondering whether my pipeline is simply not suited to the connectivity
analysis with powcorr_ortho as implemented in FieldTrip or if the function is simply not fully implemented yet. Has anyone used it successfully before?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I use the following FieldTrip (pseudo-) code:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">%% LCMV source reconstruction<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg = [];<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.method = ‘lcmv’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.keeptrials = ‘yes’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.elec = elec; <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.grid = lf; % regular grid of 1 cm resolution<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.headmodel = vol % standard_bem.mat<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.lcmv.keepfilter = ‘yes’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.lcmv.lambda = ‘5%’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.lcmv.projectnoise = ‘yes’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">source = ft_sourceanalysis(cfg, tlock_data);<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">%% pseudo-code for the computation of the virtual channel time series<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">virtChan_data = tlock_data;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">virtChan_data.label = [source.pos(:, 1), source.pos(:,2), source.pos(:,3)];<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">virtChan_data.trial = source.avg.filter * tlock_data.trial;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">%% frequency analysis of the virtual channels<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg = [];<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.method = ‘mtmfft’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.output = ‘fourier’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.keeptrials = ‘yes’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.foi = 10; % alpha band<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.taper = ‘hanning’ % I originally used 3 tapers but source code in ft_connectivity_powcorr_ortho implies that multitaper is not compatible<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">virtFreq = ft_freqanalysis(cfg, virtChan_data);<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">%% connectivity analysis<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg = [];<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">cfg.method = ‘powcorr_ortho’;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">conn = ft_connectivityanalysis(cfg,virtFreq);<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Any suggestions and/or comments would be immensely helpful! Thanks in advance.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Son<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:7.5pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE">Son Ta Dinh, M.Sc.</span><span lang="EN-US" style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:7.5pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE">PhD student in Human Pain Research</span><span lang="EN-US" style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:7.5pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE">Klinikum rechts der Isar</span><span style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:7.5pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE">Technische Universität München<br>
Munich, Germany<br>
Phone: </span><a href="tel:%2B49%2089%204140%207664" target="_blank"><span style="font-size:7.5pt;font-family:"Times New Roman",serif;color:blue;mso-fareast-language:DE">+49 89 4140 7664</span></a><span style="font-size:7.5pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE"><br>
</span><a href="http://www.painlabmunich.de/" target="_blank"><span style="font-size:7.5pt;font-family:"Times New Roman",serif;color:blue;mso-fareast-language:DE">http://www.painlabmunich.de/</span></a><span style="font-size:12.0pt;font-family:"Times New Roman",serif;color:#888888;mso-fareast-language:DE"><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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