Differential EEG

Doktor DynaSoar targeting at OMCL.mil
Wed Mar 3 18:37:48 EST 2004


On Wed, 03 Mar 2004 19:57:49 GMT, "kpaulc" <kpaulc at earthlink.net>
wrote:

} "k p Collins" <kpaulc@[----------]earthlink.net> wrote in message
} news:zMS0c.29106$hm4.12683 at newsread3.news.atl.earthlink.net...
} > "NMF" <nm_fournier at ns.sympatico.ca> wrote in message
} > news:3ft0c.2257$qA2.152895 at news20.bellglobal.com...
} > > [...]
} > [...]
} 
} > in condition 1, activation at locus A de-
} > creases, but activation at locus B can go up or
} > down, and in condition 2, activation at locus A
} > increases, but activation at locus B can go up
} > or down.
} >
} > So nothing can be said about locus A, without
} > knowing what goes on at =every= "locus B".
} >
} > It does an good to look at any "locus A" with-
} > knowing what's going on at =every= "locus B".
} > [...]
} 
} All existing EEG usage runs headlong into this
} 'difficulty', but the 'difficulty' is 'easily' overcome
} by doing "Simultaneous-Differential EEG" [SDEEG;
} which I'm discussing, for the first time, here].

You go on to describe coherence calculation using average reference. 

Mounier R.  [Real-time statistical analysis of electroencephalographic
signals: proper and mutual power density; coherence] French.
Agressologie. 1969 Jun 16;10:Suppl:519-24. 

Had you included phase in the frequency dependent measure, it would
have been complex coherence.

Grindel' OM, Gershman SG, Boldyreva GN, Vakar EM, Malina ZA.
[Intercentral relations in the cortex of the human cerebral
hemispheres according to findings of the spectrum of coherence and
phase spectrum of the EEG] Russian.
Zh Vyssh Nerv Deiat Im I P Pavlova. 1973 Jul-Aug;23(4):771-81 

Coherence requires re-referencing to average reference as a matter of
course. However, re-referencing can be and is done to any arbitrary
electrode or collection of them. Recording montage does not dictate
analysis montage. In addition, many techniques, such as current source
density, independent component analysis and Laplacian smoothing, do a
fine job of extrapolating source placement at arbitrary distances
between actual electrodes (though they are limited in number of
sources so specified to some function of the original number of
recording electrodes).

I've used high dentity recording with re-referencing (Electrical
Geodesics). 128 channels doesn't give you significantly better answers
than 64 in terms of source localization, and no better than 32 in
terms of localization of effects. What you gain in spatial resolution
you lose in statistical power due to multiple comparisons.

Even with 32 channels, two of them being VEOG and HEOG, you have 30
active channels, and that means 435 unique comparisons per test.

} Aside: Im 'smiling' as I write this because it'll be
} just one more thing that gets 'borrowed' by the
} 'profit seekers', and one more thing that, when
} I 'protest' its being 'borrowed', will result in
} folks 'thinking' that I'm 'being untoward', when
} all I'm doing is what I can to Earn a place for
} NDT's understanding.

Although computing power to calculate coherence was not commonly
available before such machines as the PDP-1, the concept was already
well understood. Even Berger had noted similarities and differences in
modulation of oscillatory activity recorded simultaneously at
different locations. That was about 75 years ago.




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