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<p class="custom-cursor-default-hover"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; text-size-adjust: auto;">Good morning,</span></p>
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I am interested in understanding the directed connectivity between the thalamus, where I am recording a Local Field Potential (in 1 channel) and the cortex, where I am recording EEGs (in 16 channels).</div>
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My signal is epoched in 4-seconds windows, and I am<span class="Apple-converted-space"> </span><b class="">not<span class="Apple-converted-space"> </span></b>interested in understanding the evolution of the directed connectivity<span class="Apple-converted-space"> </span><i class=""><b class="">in
time</b></i><span class=""><b class=""> </b>but rather just which structure is leading which.</span></div>
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I have computed<span class="Apple-converted-space"> </span><b class="">Partial Directed Connectivity<span class="Apple-converted-space"> </span></b>(pdc) with the fieldtrip function<span class="Apple-converted-space"> </span><b class="">ft_connectivityanalysis</b>,
feeding into the code the transformed, Fourier spectrum (complex double) of my signal (rpttap x channels x frequencies, where rpttap is repetitions (i.e., number of epochs) x tapers). </div>
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My final matrix of pdc is<span class="Apple-converted-space"> </span><b class="">17 x 17 x frequencies<span class="Apple-converted-space"> </span></b>(where frequencies are my frequencies of interest). The first<span class="Apple-converted-space"> </span><b class="">16
channels</b><span class="Apple-converted-space"> </span>represent the<span class="Apple-converted-space"> </span><b class="">EEG</b><span class="Apple-converted-space"> </span>channels, the<span class="Apple-converted-space"> </span><b class="">17th channel</b><span class="Apple-converted-space"> </span>is
the<span class="Apple-converted-space"> </span><b class="">LFP</b><span class="Apple-converted-space"> </span>channel in the<span class="Apple-converted-space"> </span><b class="">thalamus</b>. Let’s call this matrix<b class=""><span class="Apple-converted-space"> </span>A.</b></div>
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I have two questions:</div>
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1) Did I understand correctly that the element<span class="Apple-converted-space"> </span><b class="">A( i, j, f )<span class="Apple-converted-space"> </span></b>for a given frequency f indicates the directed connectivity<span class="Apple-converted-space"> </span><b class=""><u class="">from</u><span class="Apple-converted-space"> </span>element
i<span class="Apple-converted-space"> </span><u class="">to</u><span class="Apple-converted-space"> </span>element j?<span class="Apple-converted-space"> </span></b>(And not the other way around)</div>
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2) In my case,<span class="Apple-converted-space"> </span><b class="">A( 1:16 , j , f )<span class="Apple-converted-space"> </span></b>is a column vector containing the<span class="Apple-converted-space"> </span><b class="">same number!</b> </div>
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It looks like, independently on what EEG channel I am considering (unless I am considering the channel in the thalamus), the contribution of directed connectivity to a certain channel<span class="Apple-converted-space"> </span><b class="">j</b><span class="Apple-converted-space"> </span>is
always the same. This also stays for the thalamus, so if I take<span class="Apple-converted-space"> </span><b class="">A( 1:16, 17, f )</b>, it seems like all the eeg channels have the same directed connectivity to the thalamus. Is that possible? I think it
does not really make sense. Please notice that the numbers are not exactly the same, but differ in the 4th decimal digit. </div>
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Thank you in advance for your help</div>
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Giovanna</div>
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