Figure 9.

The effect of axon geometry on stimulation thresholds. (a) A straight axon and corticospinal axon with bends oriented parallel (solid line) and perpendicular (dashed line) to a five-electrode array. (b) The potentials (top) and the second difference of the potentials (δ²Φ, bottom) when either one (M) or five contacts (CA) in a cathodic configuration was used to stimulate the target axons. (c) The voltage required to activate 50 % of a population of modeled axons (V₅₀) when the array was oriented either parallel or perpendicular to the axons. (d) The voltage required to evoke a half maximal EMG (V₅₀) when the array was oriented parallel to the posterior internal capsule (IC, top) and sciatic nerve (bottom).