Critical amplitude curves for different periodic stimuli and different dynamical mechanisms of excitability

Critical amplitude curves for different periodic stimuli and different dynamical mechanisms of excitability are investigated numerically in the Morris-Lecar model neuron. It has been considered as a universal phenomenon that critical amplitude curves exhibit U-shaped structures in the previous investigations. Nevertheless, we find that the critical amplitude relies on not only the type of a periodic stimulus but also the dynamical mechanism of excitability of a neuron. The dynamical mechanism of excitability determines whether a neuron is a resonator or integrator. There is a U-shaped structure in the critical amplitude curve for a resonator subjected to a sinusoidal stimulus or a periodic pulse stimulus. However, in high frequency range the critical amplitude increases monotonically with the stimulus frequency for a sinusoidal stimulus and decreases monotonically for a periodic pulse stimulus. In contrast, for an integrator, the critical amplitude versus the stimulus frequency is always a monotonic curve. The change in the critical amplitude curve is shown through the Morris-Lecar model.