[FieldTrip] questions about forward calculations

[Schönherr, Margit]

Hello,

I have some questions regarding forward computations.

1) How is the definition of the EEG leadfield - does the dipole point from red to blue or from blue to red? I obtain different results when I compute the leadfield of the same dipole either with a 3-concentric-spheres volume conductor or with BEM (openmeeg).

2) In which units are the leadfields given? For the 3-concentric-spheres volume conductor, the magnitude of the field is 70, for BEM 2e-5.

3) Also for MEG, the BEM leadfield is 1e-6 times smaller than the single sphere. For the single sphere model, the field strength is 1e-5. I think, this is Tesla and corresponds to a 1 Am dipole. But the BEM forward field of the same dipole has strength 1e-11. What is the unit here?

Thanks!
Margit