<div>Hi Michael,</div>
<div> </div>
<div>thanks a lot for that suggestion. </div>
<div>The gamma activity at the sensor level might indeed be of muscular origin and this would explain why it doesn't show up inside the head.</div>
<div>Even after automatic & manual artifact rejection the patients were left with more gamma activity. To my 'untrained eye' the sensor topographies suggested that the activity would come from the brain. It didn't extend to the boundaries of the Topoplot, at least in the 60-90 Hz range. However, this was the case for other parts of the gamma-band.</div>
<div> </div>
<div>Greetings, Tobias</div>
<div> </div>
<div> </div>
<div>On Tue, May 31, 2011 at 12:44 PM, Michael Wibral <span dir="ltr"><<a href="mailto:michael.wibral@web.de">michael.wibral@web.de</a>></span> wrote:<br></div>
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<div style="BACKGROUND-COLOR: #ffffff; FONT-FAMILY: Verdana, Arial, sans-serif; FONT-SIZE: 12px" bgcolor="#FFFFFF">Hi Tobias,<br><br>it could be that the temporal activity at the sensor level is of muscular origin. Given all runs well in beamforming you shouldn't see too much of that insode the head - have you considered this possibility?<br>
<br>Michael<br><br><br><br>
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<b>Von:</b> "Tobias Navarro Schroeder" <<a href="mailto:tobiasnavarroschroeder@googlemail.com" target="_blank">tobiasnavarroschroeder@googlemail.com</a>><br><b>Gesendet:</b> May 30, 2011 5:58:32 PM<br><b>An:</b> <a href="mailto:fieldtrip@donders.ru.nl" target="_blank">fieldtrip@donders.ru.nl</a><br>
<b>Betreff:</b> [FieldTrip] Beamforming on resting state data
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<p>Hi Fieldtrippers,</p>
<div> </div>
<div>I performed DICS beamforming on resting-state data (i.e. no task, no baseline, eyes closed) of a clinical population and controls.</div>
<div>According to the sensor data the patients have more gamma-band (60-90 Hz) activity over temporal areas (somewhat spread-out).</div>
<div>Curiously, after beamforming and group comparisons with 'indepsamplesT' permutation statistics the difference map shows more gamma-band (60-90 Hz) activity for controls in the left, middle-temporal gyrus.</div>
<div>Hence, the source-level results are opposite to the sensor-level results (although more spatially confined). This is <u>not</u> a problem of the design matrix, or confusing the groups.</div>
<div> </div>
<div>Question 1: Does anybody have experience with opposite results on source and sensor level?</div>
<div> </div>
<div>The individual raw beamforming results (interpolated on the subjects' MRIs) look suspicios as well. Due to the 'unit gain constraint' there should be an overestimation of power in the center of the head, but only a minority of subjects show that. Often I see temporal or parietal activity.</div>
<div> </div>
<div>Question 2:</div>
<div> </div>
<div>Would a lack of a blob in the center of the head in individual, raw, beamforming data indicate an erroneous source analysis?</div>
<div> </div>
<div>Thanks a lot for help and suggestions.</div>
<div> </div>
<div>Best, Tobias Navarro Schröder</div>
<div> </div>
<div>ps: The configurations for calculating the covariance and the beamforming is added below:</div>
<div> </div>
<div>
<p> </p><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New"><font size="1">1) % Compute the covariance matrices </font></font></font></font>
<p> </p>
<p><font face="Courier New"><font face="Courier New"><font size="1">cfg.output = </font></font></font></p><font color="#a020f0" face="Courier New"><font color="#a020f0" face="Courier New"><font color="#a020f0" size="1" face="Courier New">'powandcsd'</font></font></font><font face="Courier New"><font face="Courier New"><font size="1">;</font></font></font>
<p><font face="Courier New"><font face="Courier New"><font size="1">cfg.foi = 75;</font></font></font></p>
<p><font face="Courier New"><font face="Courier New"><font size="1">cfg.foilim = [75 75];</font></font></font></p>
<p><font face="Courier New"><font face="Courier New"><font size="1">cfg.tapsmofrq = 15; <font color="#228b22">% 75 +- 15 = 60 - 90 Hz</font></font></font></font></p>
<p><font face="Courier New"><font face="Courier New"><font size="1">cfg.pad = </font></font></font></p><font size="1"><font color="#a020f0" face="Courier New"><font color="#a020f0" face="Courier New"><font color="#a020f0" face="Courier New">'maxperlen'</font></font></font><font face="Courier New"><font face="Courier New">; </font></font><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New">% default</font></font></font></font>
<p><font face="Courier New"><font face="Courier New"><font size="1">cfg.method = </font></font></font></p><font size="1"><font color="#a020f0" face="Courier New"><font color="#a020f0" face="Courier New"><font color="#a020f0" face="Courier New">'wltconvol'</font></font></font><font face="Courier New"><font face="Courier New">; </font></font><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New">% wavelet analysis</font></font></font></font>
<p><font face="Courier New"><font face="Courier New"><font size="1">cfg.width = 5; </font></font></font></p><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New"><font color="#228b22" face="Courier New"><font size="1">% Width of the wavelet. Determines the temporal and spectral resolution of the analysis constant.</font></font></font></font>
<p> </p>
<p><font face="Courier New"><font size="1" face="Courier New"><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New">2) % Perform the actual beamforming</font></font></font></font></font></p>
<p><font face="Courier New"><font size="1" face="Courier New"><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New">% load grids of MRI volume</font></font></font></font></font></p>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">fullnameGrid = [ CurSubject.mripath CurSubject.MRIModel];</font></font></font></font></p>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg = load(fullnameGrid);</font></font></font></font></p>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.vol = cfg.hdm;</font></font></font></font></p>
<p> </p>
<p> </p>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.frequency = 75;</font></font></font></font></p>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.method =</font></font></font></font></p><font face="Courier New"><font size="1" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New">'dics'</font></font></font><font size="2" face="Courier New"><font size="2" face="Courier New">;</font></font></font></font>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.keepfilter =</font></font></font></font></p><font face="Courier New"><font size="1" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New">'yes'</font></font></font><font size="2" face="Courier New"><font size="2" face="Courier New">; </font></font><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New">% keep the beamformer filters (virtual electrodes) for later use</font></font></font></font></font>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.keeptrial =</font></font></font></font></p><font face="Courier New"><font size="1" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New">'no'</font></font></font><font size="2" face="Courier New"><font size="2" face="Courier New">;</font></font></font></font>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.keepmom =</font></font></font></font></p><font face="Courier New"><font size="1" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New">'yes'</font></font></font><font size="2" face="Courier New"><font size="2" face="Courier New">; </font></font><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New"><font color="#228b22" size="2" face="Courier New">% useful for connectivity calculations. Dipole moments..</font></font></font></font></font>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.projectmom =</font></font></font></font></p><font face="Courier New"><font size="1" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New">'yes'</font></font></font><font size="2" face="Courier New"><font size="2" face="Courier New">;</font></font></font></font>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.projectnoise =</font></font></font></font></p><font face="Courier New"><font size="1" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New"><font color="#a020f0" size="2" face="Courier New">'yes'</font></font></font><font size="2" face="Courier New"><font size="2" face="Courier New">;</font></font></font></font>
<p><font face="Courier New"><font size="1" face="Courier New"><font size="2" face="Courier New"><font size="2" face="Courier New">cfg.latency = 1;</font></font></font></font></p></div></div></div></div></blockquote></div>
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