[Eeglablist] Standardize electrodes montage for group analysis

[Chadwick Boulay]

I think the assumption is that if brain A is 10% larger than brain B 
then the cortical region normally associated with C3 is 10% further from 
the midline in brain A than it is in brain B. Thus, if you are using 
differently-sized caps (with different electrode spacing) for 
differently-sized heads then you may assume that C3 from subject A 
represents approximately the same patch of brain as C3 from subject B. 
The precise coordinates of C3 don't matter.

Of course the above assumption is false not only because the head shapes 
vary but also because the relative skull conductance and brain 
curvatures vary. While having super-accurate coordinates might help 
overcome the problem of head shape, it won't help with the other 
problems. If you have anatomical MR images for each subject and you are 
able to coregister your electrode positions with the MRI then you may be 
able to use ICA+NFT+DIPFIT to identify subject-specific neurobiological 
'sources'. You may then use some component-clustering algorithm to 
figure out which component from each subject represents a particular 
patch of brain then do your between subject/group comparisons on those 
components' activations. (Notice that I skipped over the 
skull-conductance problem.)

If you need to identify precise (not necessarily accurate) brain regions 
associated with your task then the above method might be for you. 
However, if you REALLY need to identify brain sources accurately then 
you might be better off going with fMRI or EEG-fMRI if time-resolution 
is important.

If you don't need to report specific brain regions then I'd just stick 
with averaging across electrodes with the same name.

On 2/20/2013 9:47 AM, Iman M.Rezazadeh wrote:
>
> Dear all,
>
> Since each subject has its own head diameter thus electrode placement 
> over the head might be slightly different !
>
> Thus, do you have any idea how to standardize the electrode 
> configuration from different subjects for within or btw group comparison!
>
> I am using spline interpolation to convert my 128 channel data to 81 
> channel. However the new coordinates are still slightly different from 
> subject to subject!
>
> Any thought???
>
> Iman M.Rezazadeh, PhD
>
> Postdoctoral Research Fellow
>
> Center for Mind and Brain
>
> University of California, Davis
>
> www.linkedin.com/pub/iman-m-rezazadeh/10/859/840 
> <http://www.linkedin.com/pub/iman-m-rezazadeh/10/859/840>
>
> http://mindbrain.ucdavis.edu/people/imanmr
>
> email : irezazadeh at ucdavis.edu <mailto:irezazadeh at ucdavis.edu>
>
> Tel: 530-297-4444
>
> Cell:310-490-1808
>
> Skype: Imanmr
>
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