[Mne_analysis] Large mean voltages in BEM EEG forward model.

[Justin Ales]

I'm confused. I don't understand the hypothetical potential
distribution in your example. I thought the  forward operator should
take into account the reference of the electrode measurement montage.
The sum of the potentials over the electrodes in the recorded data
would be 0 because of the explicit average referencing.

Justin


On Tue, Sep 30, 2008 at 1:18 PM, Yury Petrov <y.petrov at neu.edu> wrote:
> I think that the MNE forward matrix is just the distribution of potentials
> on your electrodes produced by a current dipole at a given location times
> all such locations. There is no reason for the sum of potentials over the
> electrodes to be always 0. For example, if the electrodes cover mostly the
> area of the scalp to where one pole of the dipole points, then the averaged
> potential will be quite different from zero. You could add a constant
> potential to turn the average to zero, but this would only work for one
> dipole out of many.
>
> On Sep 30, 2008, at Sep 30, 2008 | 3:54 PM, Justin Ales wrote:
>
>> Hi,
>>
>> I've been looking at the forward computations generated by MNE.  I've
>> been generating my fif files from data I have in matlab. I have an
>> average reference montage, and when I look at the forward model there
>> are large variations in the average across channels.  Since it is an
>> average reference montage I expected the forward model to have zero
>> mean. I'm not sure if I don't understand the forward model output from
>> MNE, or if I'm not importing my data correctly.
>>
>> Thanks,
>> Justin Ales
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