Previously, we have demonstrated the excitation boundaries for the tripolar electrode configuration with a 3 mm spacing between the edges of the three contacts, for reference, shown here (on the right). Let’s look at the same configuration with a 6 mm separation between contacts. The application of a -1.237 V stimulus produces a region activated as indicated by the boundary Jth, not too different from the tripolar configuration with closer spacing. However at this stimulus magnitude all 20 µm axons in the fascial are activated, a substantial difference in the selectivity compared to the more closely spaced contacts. Doubling the 10 µm stimulus current the boundary for the 10 µm activation limit is larger than that, that was observed with the closer spaced contact. Keep in mind that stimulation of fiber populations may have different goals. If the goal is to activate every fiber in the fascicle at the lowest stimulus intensity the choice of the electrode configuration could be different than if the goal was greater control of which populations are caused to be activated.
RR Chintalacharuvu, DA Ksienski, JT Mortimer, Annual Int Conf of the IEEE Engr in Med and Biol Vol 13, No 2 1991, pp 0912-13
Rekha R. Chintalacharuvu, A Numerical Analysis of the Electric Field Generated by the Nerve Cuff Electrode, MS thesis, 1991 Case Western Reserve University