Forward model conductivities

[Dr. Carsten Wolters]

Dear Stanley and Paul,

I agree to what Stanley wrote about the skull inhomogeneities, it fits
perfectly
to what we described in a recent publication:
@Article{CHW:Dan2010,
    author = {Dannhauer, M. and Lanfer, B. and Wolters, C.H. and
Kn{\"o}sche, T.},
    title = {Modeling of the Human Skull in {EEG} Source Analysis},
  journal =      "Human Brain Mapping",
  note    =      "DOI: 10.1002/hbm.21114, PMID: 20690140",
  year =         "2010",
}
Best regards
    Carsten

Stanley Klein wrote:
> Dear Paul and Carsten,
> The conductivity ratio of 1/20 that you mention is indeed on the low
> side of
> many present estimates. It is way lower than the Rush  &  Driscoll  1/80
> ratio that we used in our 30 year old "Ary Correction" paper that
> examined
> the effect of skull and scalp thickness. My big worry however is
> not simply to find the ratio (taking individual differences into
> account). but
> also to get estimates of the differences in conductivity across the skull.
> I'm pretty confident that such inhomogeneities are present and that
> they will
> have significant effects on the BEM forward models. The inhomogeneities
> will not only affect the effective depth of sources but also can
> laterally shift
> their locations to places on cortex with very different surface normals.
>
> An important aspect of our EEG/MEG source localization work is to learn
> how to calibrate each individual's conductivity partly based on
> differences
> in EEG vs MEG localizations.
>
> best,
> Stan
>
>
>
> On Mon, Oct 25, 2010 at 4:40 AM, Paul Czienskowski <paul_c at gmx.de
> <mailto:paul_c at gmx.de>> wrote:
>
>     Dear all,
>
>     Alexandre Gramford pointed out to me that there was some
>     discussion ongoing on which conductivities to use for
>     EEG-Forward-Modeling and I'd like to move this discussion more to
>     public for it could be interesting for many of us.
>     I was recently overflying some papers concerned with that very
>     issues and I made some interesting and discoveries, especially in
>
>         Conductivity of living intracranial tissues. by Latikka J,
>         Kuurne T, Eskola H.
>         The electrical conductivity of human cerebrospinal fluid at
>         body temperature by Baumann et al.
>
>     The first one measured the conductivities (or resistivities) of
>     living brain tissue and came to values of 3.51 Ohms*m and 3.91
>     Ohms*m for grey respectively white matter and 0.80 Ohms*m for the
>     CSF (which are about 0.28, 0.256 and 1.25 S/m). In contrary the
>     second one found a value for 1.79 S/m for CSF at body temperature
>     where it was about 1.4 S/m at room temperature. The Skull-To-Brain
>     conductivity ratio was measured for example in
>
>         Estimation of /in vivo/ brain-to-skull conductivity ratio in
>         humans by Yingchun Zhang, Wim van Drongelen, and Bin He
>
>     where they found a ratio of about 1/18.7 which is way larger than
>     the commonly assumed value.
>
>     I would appreciate very much if many of you could contribute to
>     this discussion by telling us which values you use for the
>     conductivities and on which publications the are based.
>
>     Best,
>     Paul
>
>     --
>     Paul Czienskowski
>     Max Planck institute for human development
>     Lentzeallee 94
>     14195 Berlin
>
>     Björnsonstr. 25
>     12163 Berlin
>
>     Tel.: (+49)(0)30/221609359
>     Handy: (+49)(0)1788378772
>
> ------------------------------------------------------------------------
>


--
PD.Dr.rer.nat. Carsten Wolters
Institute for Biomagnetism and Biosignalanalysis
University of Muenster, 48149 Muenster, Germany
Tel.: +49/(0)251-83-56904
Fax:  +49/(0)251-83-56874
http://biomag.uni-muenster.de

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