Pulse propagation and failure in the discrete FitzHugh-Nagumo model subject to high-frequency stimulation
We investigate the effect of a homogeneous high-frequency stimulation (HFS) on a one-dimensional chain of coupled excitable elements governed by the FitzHugh-Nagumo equations. We eliminate the high-frequency term by the method of averaging and show that the averaged dynamics depends on the parameter $A=a/\ensuremath{\omega}$ equal to the ratio of the amplitude $a$ to the frequency $\ensuremath{\omega}$ of the stimulating signal, so that for large frequencies an appreciable effect from the HFS is attained only at sufficiently large amplitudes. The averaged equations are analyzed by an asymptotic theory based on the different time scales of the recovery and excitable variables. As a result, we obtain the main characteristics of a propagating pulse as functions of the parameter $A$ and derive an analytical criterion for the propagation failure. We show that depending on the parameter $A$, the HFS can either enhance or suppress pulse propagation and reveal the mechanism underlying these effects. The theoretical results are confirmed by numerical simulations of the original system with and without noise.