In represents the nth point current source and rn represents the distance between the point source and the recording electrode, with n = 1… N, where N is the number of individual point sources. For electrodes larger than an ideal point electrode, Ve can be solved at multiple locations of the surface area of the microelectrode and then averaged. The larger the electrode area, the larger the averaging effect (Grimnes and Martinsen, 2008). Anisotropy can also be incorporated in this model easily (Nicholson and Freeman, 1975). However, more complex geometries of, e.g., the MEA device (such as in vivo neural probes) or an inhomogeneous medium generally require a finite element method to solve for the electric field and the potential at the electrode.
