Figure 1

Schematic of the scaling of treatments applied along the surface of an axon. A mathematical analysis (see Supplement, Section 1) demonstrates that the equivalent length of a treatment applied along an axon’s surface scales as the ratio of the square root of the axon diameter. In the illustration shown, D1, diameter of the larger axon, is four times D2, the diameter of the smaller axon, and thus the equivalent effect on the large axon (L1) is twice as long as that needed to affect the smaller diameter axon (L2). This implies that less radiant exposure would be required to block the smaller-diameter axon than the larger-diameter axon.