Conduction Block in Unmyelinated Nerves Using High Frequency AC Stimulation

High frequency alternating current (HFAC) blocks conduction of action potentials through myelinated nerve fibers. This property may have clinical applications in the treatment of unwanted neural activity. The isolated response of unmyelinated nerves to HFAC stimulation has not been studied previously. In this study, sinusoidal HFAC stimulation was used to reversibly block conduction of action potentials through the unmyelinated nerve fibers of Aplysia californica. Complete reversible block was found at frequencies from 5 kHz to 50 kHz. The minimum HFAC amplitude for block was between 1 mA and 6 mA. An asynchronous firing phase preceded the block phase at all frequencies. Unlike myelinated nerves, the minimum HFAC amplitude for inducing block did not have a monotonically increasing relationship with frequency, as an exponential decrease in the blocking amplitude was observed for frequencies above 12 kHz