[Eeglablist] del2map()

Tom Campbell tom.campbell at helsinki.fi
Thu Dec 15 07:25:04 PST 2005

Dear eeglab experts,

I am trying to a scalp current density analysis with EEGLAB. One approach 
to doing this is to "take the spatial derivative of spherical spline 
functions" and the consequent value comes out in mA/m3. For instance, an 
N1 of 10 uV would lead to corresponding scalp current density analysis 
values of 2 milli-A/m3.

e.g. Alcaini, Giard, Thevenet, Pernier (1994) Psychophysiology 31, 611-615.

I see there is a function called del2map() that I think performs this 
whole operation for the points at electrodes only and not the interpolated 
points using the input of a .loc file, denoting the locations of the 
electrodes, and vector of amplitudes. Is there a difference between a the 
discrete laplacian and a surface laplacian?

When I input this vector of amplitudes in uV (e.g. 2.6) I get the 
corresponding output of a much lower order (e.g.2.6 uV -> 0.0017). Please, 
is this output expressed in Amps/m3 or something else?

I have then tried using the headplot() function that seems to produce 
plausible distribution maps, that I take interpolates across the surface 
of a model of the scalp. Taking the whole process together, please, is 
this functionally-identical to "taking the spatial derivative of spherical 
spline functions"?   
best regards,
Tom Campbell                             e-mail:tom.campbell at helsinki.fi
Helsinki Collegium for Advanced Studies  tel: +358-9 191 23256
University of Helsinki, Finland          fax: +358-9 191 22924
P.O.Box 4 (Fabianinkatu 24)              home: +358-4 154 09764 
FIN-00014 University of Helsinki

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