FitzHugh-Nagumo model. Temporal alternation

Here we add excitation cI(t) with period T to the FHN system
    du/dt = F(u, v) + c I(t) = u(1 - u)(u - a) - v + cI(t),
    dv/dt = H(u, v) = ε (bu - v),
    I(t) ~ [cos(πt/T)]500,     δI(t)dt = 1.

For small T the system is not ready for the second excitation cycle.
a b ε c T

dt Ymin Ymax field
Again to the left the phase plane of the system is shown. F(u,v) = 0 null cline is the red line and H(u,v) = 0 null cline is the green line. To the right u(t) excitation (black) and v(t) recovery (blue) variables are plotted. You can explore the model for different parameter values.
Heart rhythms     updated 3 Dec 2011