Effect of Contact Spacing

The effect of distance between the contacts of the tripolar configuration, 3mm (left) and 6 mm (right) are shown in the figure. The threshold was lowered with increase in contact spacing.
There was a shift in the activation contour of the 20 µm axons for both the Jth and 2Jth values. The results appear to show that smaller inter-contact distances are more efficient in localizing the applied currents.

Conclusions

Anisotropy, perineurium and connective tissue were barriers to the current flow between the electrode and the nerve fiber.
Perineurium and connective tissue decrease the selectivity of excitation of specific regions of the nerve.
Anodic current from an electrode across from the cathode improved the selective excitation of specific regions for both monopolar and tripolar electrode configurations.
Tripolar electrodes provided greater selectivity than monopolar electrodes
Smaller spacing between the anodes and the cathode in a tripolar configuration was more efficient in confining the current to regions closer to the electrode.
Snugly fitting cuff reduced the scattering effect of the saline layer present between the implanted cuff and the nerve.