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Dear Johaness,

Some guidelines about the number and placement of electrodes in general can
be found in the review by Michel et al. EEG source imaging, Clinical
Neurophysiology 115 (2004), 2195 -2222. Basically what they are saying
is that 64 channels are much better than 32 but increasing the number above
64 improves things just a little more.
Best,

Vladimir


On Fri, Apr 18, 2008 at 9:30 AM, Stefan Kiebel <[log in to unmask]>
wrote:

> Hi Johannes,
>
> there is no problem in using DCM with 32 channels. This is my personal
> experience; no one has done a formal comparison of using DCM with different
> number of channels or montages.
>
> Keep in mind that DCM can be seen as a source reconstruction exploiting
> temporal constraints. That means, with respect to the spatial resolution of
> sources, you face the same issues as conventional source reconstruction of a
> single time point. In particular, typical setups for EEG (sensors on the
> upper half of the head) are probably suboptimal in resolving source
> z-direction parameters in the temporal lobes (both orientation and
> location). In other words, it depends mostly on the experimental question
> you want to ask, and whether your sampling allows to resolve the crucial
> parameters (both time and space). I personally would, if in doubt, use as
> many channels as possible.
>
> All the best, Stefan
>
> Is there an optimal number of EEG channels for a DCM analysis? We're
> > thinking of using either 32 or 64 channels for recording. It would, of
> > course, be time-saving to use only 32, but we're worried about not
> > getting
> > the best results with 32 channels.
> >
> > I'd be thankful for your suggestions!
> >
> > Johannes Klackl, University of Salzburg
> >
> >
> >
> >
>
>
>  --
> Dr. Stefan Kiebel Wellcome Trust Centre for Neuroimaging
> Institute of Neurology, UCL 12 Queen Square London WC1N 3BG
> Phone: (+44) 20 7833 7478 Fax:   (+44) 20 7813 1420
>