Selective Activation

Scattering Effects of Tissue Conductivities


Our next step is to explore the scattering effects of the tissues that form around the cuff of an implanted electrode. Starting with a cuff, that is slightly larger than in the previous cases and has a saline layer next to the cuff we add at connective tissue layer. Point “A” is in the same position relative to the center of the 3 mm nerve. A stimulus of -1.209 V is required to activate a 10 µm axon at point “A” and the region occupied by all other 10 µm axons in the fascicle are indicated the by the boundary labeled Jth. At this stimulus magnitude all 20 µm axons in the fascicle are activated. At 2Jth almost all 10µm axons in the fascicle are activated. Interestingly, an island of inactivated 10 µm axons exists in the interior of the fascicle. For comparison, the results for the same fascicle but without the encapsulating scattering barrier in shown here. I have previously called to your attention the increasing concavity downward as scattering barriers are introduced. As scattering barriers are introduced more and more current is deflected to surround the fascicle, creating a longitudinal potential difference in the interior of the fascicle to cause nearby axons to be the 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