Optimal noise for periodic output in excitable FitzHugh-Nagumo systems
Coherence resonance (Pikovsky & Kurths 1997) is a counterintuitive phenomenon where an excitable system (like a neuron near threshold) produces its most regular oscillations at an intermediate, optimal noise level — not at zero noise. The FitzHugh-Nagumo model dv/dt = v − v³/3 − w + σξ, dw/dt = ε(v + a − bw) is used here. Too little noise: rare, irregular spikes. Optimal noise: near-periodic firing. Too much noise: chaotic, incoherent bursting. The coefficient of variation CV = σ_ISI/⟨ISI⟩ reaches a minimum at optimal noise — the signature of coherence resonance.