Coherence resonance in a Hodgkin-Huxley neuron

We study the nonlinear response of the Hodgkin-Huxley model without external periodic signal to the noisy synaptic current near the saddle-node bifurcation of limit cycles. The coherence of the system, estimated from the interspike interval histogram and from the power spectra of membrane potentials and spike trains, is maximal at a certain noise intensity, so that the coherence resonance occurs. The mechanism of this phenomenon is found to be different from previously studied models of coherence resonance and explained in terms of rigid excitations of periodic oscillations, and the combined effect of amplitude and phase fluctuations.