[Eeglablist] Coherence or Correlation among set of electrodes

Tue Oct 16 14:53:02 PDT 2012

Greg, just to bring you up to speed, nowadays most researchers working with
EEG or MEG quite rarely use simple FFT periodogram analysis. Wavelets or
multi-tapers are routinely preferred (and have been available, for
instance, in EEGLAB and Fieldtrip for many years).

I'm not sure I follow your argument that spectral decompositions need be
performed at the active electrode site. Many (if not most) research-grade
EEG hardware solutions already utilize unity-gain active electrodes which
significantly reduces signal degradation and noise contamination prior to
high-precision ADC. The spectral decomposition is then performed in
software. Is your argument that this noise reduction is still insufficient
and that the situation would be vastly improved by performing ADC and
spectral analysis at each electrode? I'm curious if you might detail how
that would be the case.

Also, to what are you referring when you say "current generation FFT-based
analysis hardware?" Because, in most research (and clinical) practices,
spectral analysis is performed in software (although, of course an
equivalent analog circuit *could* be used -- at least for something as
simple as a DFT).

Tim

On Tue, Oct 16, 2012 at 11:42 AM, Gregory Perry
<Gregory.Perry at govirtual.tv>wrote:

>  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.
>
> 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.
>
> 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.
>
> From a technology standpoint, current generation FFT-based EEG analysis
> hardware is pretty archaic IMHO.
>
>
>  *From*: Jeff Eriksen [mailto:eriksenj at ohsu.edu]
> *Sent*: Tuesday, October 16, 2012 02:18 PM
> *To*: Gregory Perry; eeglablist at sccn.ucsd.edu <eeglablist at sccn.ucsd.edu>
> *Subject*: Re: [Eeglablist] Coherence or Correlation among set of
> electrodes
>
>  I have several comments on this post:
>
>    1. Hardware has nothing to do with it – it is software that allows us
>    to localize and correlate
>    2. "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
>    3. Active electrodes are good for reducing noise and the use of gel,
>    but provide nothing to help with localization or correlation analysis
>    4. "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
>    5. A lot of 3D analysis and research is going on – perhaps you are
>    only familiar with clinical systems?
>
> -Jeff Eriksen
>
>   From: Gregory Perry <Gregory.Perry at govirtual.tv>
> Date: Monday, October 15, 2012 7:52 PM
> To: "Iman M.Rezazadeh" <irezazadeh at ucdavis.edu>, "eeglablist at sccn.ucsd.edu"
> <eeglablist at sccn.ucsd.edu>
> Subject: Re: [Eeglablist] Coherence or Correlation among set of electrodes
>
>    Even the most recent generation EEG acquisition hardware leaves a lot
> to be desired in terms of 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.
>
>  Current EEG analysis methods are stuck in a 2D world unfortunately.
>
>  ------------------------------
> *From:* eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu]
> on behalf of Iman M.Rezazadeh [irezazadeh at ucdavis.edu]
> *Sent:* Monday, October 15, 2012 8:17 PM
> *To:* eeglablist at sccn.ucsd.edu
> *Subject:* [Eeglablist] Coherence or Correlation among set of electrodes
>
>   Hi,
>
> 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 ?
>
>
>
> Best,
>
> Iman
>
>
>
> Iman M.Rezazadeh, PhD
>
> Center for Mind and Brain
>
> University of California, Davis
>
> irezazadeh at ucdavis.edu
>
> cell:310-490-1808
>
>
>
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