extracellular stimulation without a "ground"

[goody7]

My problem might be more of a conceptual one.
Scenario: Neurons are getting stimulated via an electric field in the head. This electric field was created by a time-varying magnetic field - so there is no inherent ground per se. I am using the "extracellular" mechanism to run some quick experiments on a single section, 3 segment neuron model. This neuron is, in essence, seeing 3 different potentials (for simplicity sake, lets say they are quick step inputs ~1ms long). The neuron isn't responding the way I expected. I read the programmer's reference about the "extracellular" mechanism (particularly the part about it doing damage to my intuition). Needless to say, I feel like I am on shaky ground (no pun intended):

In this case, because I am not using a micro-electrode, there is essentially no "xc", "xg", or "xraxial". Does this mean that I can model the voltages as "vext"?

Thanks,
Brian

[ted]

Suggest you follow the same approach used by Pashut et al.
Pashut T, Wolfus S, Friedman A, Lavidor M, Bar-Gad I, et al. (2011)
Mechanisms of Magnetic Stimulation of Central Nervous System
Neurons. PLoS Comput Biol 7(3):e1002022
Their source code is available from ModelDB via accession number 138321.

[goody7]

Thanks!