Comparison of numerical simulations performed by IA to the data measured in vivo . Electric current vs. voltage relationships I(U) calculated in nonlinear models (with linear and exponential σL(E)), calculated in linear models (with σL(E) = σ0 = const.) and measured in vivo by using needle electrodes with diameters: A. 0.3 mm, B. 0.7 mm and C. 1.1 mm.