The authors show that the terminal zone of an axon bundle can generate a strong dipolar extracellular field. This is particularly the case in the auditory brainstem of barn owls (and most likely of mammals), where there is a strong extracellular potential (several mV) locked to the sound, called the neurophonic. The idea is quite simple. In the terminal zone, the axons bifurcate then terminate., so that the number of axons increases, then decreases. If the wavelength of the propagating wave is right, then current is drawn into the region where axons bifurcate and exits where they terminate. This is shown numerically and theoretically, and compared to data in barn owl nucleus laminaris. One point I am wondering about is the role of axon diameters in the phenomenon; indeed at an axon bifurcation, diameters of daughter branches tend to be smaller than that of the primary branch, so one might wonder whether that might not counterbalance the increase in axon number.