Selective Activation: Part 1 : Page 4

		Department of Biomedical Engineering
	middle	Applied Neural Control: J.T. Mortimer
		Tue. Nov 26 2024

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Selective Activation: Part 1: Page 4

Effect of Tissue Conductivity

In an isotropic, homogenous, unifascicular nerve, with conductivity equal to saline, (left of figure), V thr (A/10µm) (the threshold voltage stimulus required to activate a 10 µm axon at point A) was determined to be –0.1043 Volts. The Jth and 2Jth contours for 10 Mm axons are shown. All 20 µm axons were activated at 2J, twice the V thr (A/10µm).
The activation contours in an anisotropic nerve, with longitudinal conductivity of 1.0 S/m and transverse conductivity of 0.1 S/m, is shown in the center of the figure. The V thr (A/10µm) increased to –0.1651.
With a perineurium of conductivity 0.00063 S/m, the V thr (A/10µm) increased to –0.5161 Volts, the activation contours are shown in right side of figure. All 20 µm axons were activated with 2J (twice threshold for 10 µm axons).

Effect of Electrode Configuration

The tripolar electrode configuration had two anodes located 3 mm from the central cathode. In the figure, the activation contours for monopolar and tripolar configurations are shown. A higher V thr (A/10µm) was required for the tripolar electrode. In the monopolar, all 20 µm axons were activated, whereas with the tripolar the Jth and 2Jth contours for the 20 µm axons can be seen.

Steering

A positive 0.557 Volts was applied to the steering Anode across from the central Cathode. This was the subthreshold amplitude for 20µm axons at location A. With the monopolar electrode, a significant change can be seen with addition of a steering voltage (Top right of figure).
The effect of steering with the tripolar configuration can be seen in the bottom right of the figure. The contours were similar to the Monopolar with steering, but the 2Jth area for the 20µm axons were further reduced.

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