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<font style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">No, not a high sampling rate, that's a given - active electrodes directly on the scalp performing waveform analysis, and all sharing a high resolution clock reference between all
other active electrode sites. In this fashion exact areas in the brain can be pinpointed for analysis, based on correlating acquired "time of flight" data from each electrode site - triangulation of EEG emanations to specific brain regions.<br>
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The use of FFT for EEG waveform analysis is antiquated as well, too much information is lost with only Fourier sine and cosine functions to sample and store acquired EEG data. A wavelet-based approach to EEG acquisition and waveform storage would be far superior
to FFT based on wavelet's infinite basis functions, and would more accurately preserve acquired EEG waveforms.<br>
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Something along the lines of an NV Tegra-series microprocessor as the core for an active electrode would be ideal for this. The Tegra series include an integrated GPU that could be used for offloading computationally expensive wavelet analysis functions, yet
is low powered enough to be used as a high performance active electrode able to communicate between other electrode sites for high resolution timebase correlation.<br>
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From a technology standpoint, current generation FFT-based EEG analysis hardware is pretty archaic IMHO.<br>
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<font style="font-size:10.0pt;font-family:"Tahoma","sans-serif""><b>From</b>: Jeff Eriksen [mailto:eriksenj@ohsu.edu]
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<b>Sent</b>: Tuesday, October 16, 2012 02:18 PM<br>
<b>To</b>: Gregory Perry; eeglablist@sccn.ucsd.edu <eeglablist@sccn.ucsd.edu> <br>
<b>Subject</b>: Re: [Eeglablist] Coherence or Correlation among set of electrodes
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<div>I have several comments on this post:</div>
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<li>Hardware has nothing to do with it – it is software that allows us to localize and correlate</li><li>"hi-res timebase" I suppose means a high sampling rate – this will not help much either as volume conduction is close to the speed of light</li><li>Active electrodes are good for reducing noise and the use of gel, but provide nothing to help with localization or correlation analysis</li><li>"triangulation" implies what the field calls source localization/imaging/analysis etc, and there is a vast body of knowledge and literature on this broad topic available – including using individual cortical folding patterns for modeling the putative generators</li><li>A lot of 3D analysis and research is going on – perhaps you are only familiar with clinical systems?</li></ol>
<div>-Jeff Eriksen</div>
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<span style="font-weight:bold">From: </span>Gregory Perry <<a href="mailto:Gregory.Perry@govirtual.tv">Gregory.Perry@govirtual.tv</a>><br>
<span style="font-weight:bold">Date: </span>Monday, October 15, 2012 7:52 PM<br>
<span style="font-weight:bold">To: </span>"Iman M.Rezazadeh" <<a href="mailto:irezazadeh@ucdavis.edu">irezazadeh@ucdavis.edu</a>>, "<a href="mailto:eeglablist@sccn.ucsd.edu">eeglablist@sccn.ucsd.edu</a>" <<a href="mailto:eeglablist@sccn.ucsd.edu">eeglablist@sccn.ucsd.edu</a>><br>
<span style="font-weight:bold">Subject: </span>Re: [Eeglablist] Coherence or Correlation among set of electrodes<br>
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<div style="direction: ltr; "><font size="2">Even the most recent generation EEG acquisition hardware leaves a lot to be desired in terms of </font>correlating areas within the brain that are interrelated. This doesn't seem like a hard problem to solve with
active electrodes placed at each 10/20 region, if they all shared a high resolution time base. Think reverse GPS, by measuring timing variances between each electrode site (and especially at EEG spectrum frequencies), there is no reason why specific physical
regions in the brain could not be triangulated for analysis. For extra credit, cortical folding patterns could be integrated with the acquired data to derive subject-specific brainwave signatures.</div>
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<div style="direction: ltr; ">Current EEG analysis methods are stuck in a 2D world unfortunately.<br>
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<div id="divRpF295272" style="direction:ltr"><font face="Tahoma" size="2" color="#000000"><b>From:</b>
<a href="mailto:eeglablist-bounces@sccn.ucsd.edu">eeglablist-bounces@sccn.ucsd.edu</a> [<a href="mailto:eeglablist-bounces@sccn.ucsd.edu">eeglablist-bounces@sccn.ucsd.edu</a>] on behalf of Iman M.Rezazadeh [<a href="mailto:irezazadeh@ucdavis.edu">irezazadeh@ucdavis.edu</a>]<br>
<b>Sent:</b> Monday, October 15, 2012 8:17 PM<br>
<b>To:</b> <a href="mailto:eeglablist@sccn.ucsd.edu">eeglablist@sccn.ucsd.edu</a><br>
<b>Subject:</b> [Eeglablist] Coherence or Correlation among set of electrodes<br>
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<p class="MsoNormal">Hi, </p>
<p class="MsoNormal">Just wonder if there is a way to calculate the coherence measure between two regions( set of channels—instead of two single channels) in EEGLAB or any other software? In other word, how can we find regions in the brain which their activities
are mostley related to each other using EEG ?</p>
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<p class="MsoNormal">Best,</p>
<p class="MsoNormal">Iman </p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span style="font-family: Arial, sans-serif; ">Iman M.Rezazadeh, PhD</span></p>
<p class="MsoNormal"><span style="font-family: Arial, sans-serif; ">Center for Mind and Brain</span></p>
<p class="MsoNormal"><span style="font-family: Arial, sans-serif; ">University of California, Davis</span></p>
<p class="MsoNormal"><span style="font-family: Arial, sans-serif; "><a href="mailto:irezazadeh@ucdavis.edu" target="_blank">irezazadeh@ucdavis.edu</a></span></p>
<p class="MsoNormal"><span style="font-family: Arial, sans-serif; ">cell:310-490-1808</span></p>
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