Deep Brain Stimulation (DBS) has revealed a convincing clinical efficacy in Parkinson's diseases and essential tremor. Unfortunately, to date no clear understanding of the therapeutic mechanisms has been achieved. Characterization of the distribution of the electrical quantities inside the target areas of the central nervous system is one fundamental step ahead. Starting from the studies that so far addressed this issue, aim of this work is to quantify the role of some parameters, such as dimensions of the conducting domain and of boundary conditions, on the distribution of the fundamental electric quantities inside the brain target area.