Selectivity of five tripolar electrode designs in model of Patient 2.

<p>(a) The percent of dorsal column (DC) fibers activated with no dorsal root (DR) fiber activation (<i>i.e.,</i> DC₀) when the electrode was placed along the midline, 1 mm above (<i>top</i>) and below (<i>bottom</i>) the spinal cord. DC₀ is shown above the spinal cord. For comparison, the range of DC₀ across all patients is shown below each panel. (b) Proportion of DC fibers activated versus proportions of the DR fibers activated (<i>i.e.,</i> DC_X) for three electrode designs in the extradural (<i>left</i>) and intradural (<i>right</i>) cases. The inset shows a close-up of the curves. LT = longitudinal tripolar, TT = transverse tripolar, AT = angular tripolar, and the number after the hyphen indicates the interelectrode spacing in mm.