The effect of anisotropy on the potential distribution in biological tissue and its impact on nerve excitation simulations

We present a finite difference solution of the potential distribution assoc iated with electrical current stimulation in an anisotropic in-homogeneous tissue environment and compare it to the isotropic case. The results demons trate that there can be significant errors associated with the assumption o f isotropic tissue properties in calculating the potential distribution alo ng an axon in nerve excitation simulations. These errors can have a signifi cant impact on predicted nerve fiber recruitment patterns when evaluating t he efficacy of specific surface or intramuscular stimulus electrode configu rations, The results of this study also suggest when a more comprehensive t issue model should be implemented in an electrode design study. Simulation results indicate that the isotropy assumption is worst under bipolar electr ode stimulation as opposed to monopolar stimulation and that the bipolar er ror increases as the distance between electrodes decreases. In light of the se results, it is concluded that in order to avoid large errors in the calc ulated potential distribution along an axon, the isotropy assumption should only be used when the transverse depth fi om the electrode to the nerve is relatively small.