Conduction block induced by high frequency AC stimulation in unmyelinated nerves

The potential neurophysiological applications of high frequency AC stimulation (HFAC) in blocking conduction has led to a series of experimental and modeling studies analyzing the effect of HFAC conduction block on mixed nerves. However, many of these computational studies have been based on axon models that are perhaps not valid for the nerves under study. The isolated response of unmyelinated nerves to HFAC has also not been previously studied. In this study, 5-50 kHz sinusoidal HFAC stimulation waveforms were used to reversibly block conduction through the unmyelinated nerve fibers of Aplysia. Unlike myelinated nerves, the minimum HFAC amplitude for blocking conduction in these nerves showed a non-monotonic behavior with frequency. The Hodgkin-Huxley model did not accurately predict the experimentally observed trends but modifying the model to incorporate a frequency-dependent membrane capacitance resulted in a significant change in the high frequency response of the model while still preserving the standard characteristics of action potential propagation.