(A) Conduction velocity of conditioning (horizontal line) and test (filled circles) pulses plotted as a function of interspike interval (ISI). The graph shows the refractory and supernormal phases, where the velocity of the test pulse is, respectively, less or more than that of the conditioning pulse. Simulations were done with two constant pump currents: Ipump,LO and Ipump,HI, respectively equal to the mean value of Ipump during minute 1 and minute 5 of the 10 Hz Poisson stimulation (Figure 2). Horizontal lines show the velocity of the conditioning spikes. (B) Data of panel A plotted as conduction delay vs. Finst (=1/ISI), together with the Poisson stimulation results of minutes 1 and 5 (from Figure 2D). Solid curves are polynomial fits for the Ipump,LO and Ipump,HI datasets. (C) Paired-pulse stimulations of the Hodgkin-Huxley model axon show similar refractory and supernormal phases. (D) The data from the panel C compared with the Poisson stimulation data (from Figure 2H) of the Hodgkin-Huxley model axon show a perfect match.