Exact nonequilibrium potential for the FitzHugh-Nagumo model in the excitable and bistable regimes

We obtain an analytically exact nonequilibrium potential for the space-independent FitzHugh-Nagumo model, valid in the excitable and bistable regimes ~in the limit of small noise!. This potential allows us to characterize the nature of the barrier in the excitable regime and, after subjecting the system to a modulated weak signal that rocks the potential inducing the phenomenon of stochastic resonance, to calculate the signalto-noise ratio in the bistable regime. @S1063-651X~98!08506-7#