Illustration of the model used for the leading/trailing dipole simulation of the extracellular fields near a conducting sphere. R is the distance of the recording electrodes from the center of the axon. The distance between the leading and trailing dipoles is taken as 6 mm. The nerve is stimulated on the left side (negative z values) and propagates toward the right side. The sphere is taken as highly conducting with a radius of 1 mm and is placed 1.1 mm below the nerve. The center of the sphere is taken at z = 0.