Fig 2. Phase space diagrams for spatially homogenous dynamics.
A-C) Phase space for the FitzHugh-Nagumo Eqs (7) and (8) with a = 2, I = 0 (A), a = 0.04, I = 2 (B), and a = 0.4, I = 2 (C). D-F) Phase space for the dynamic Eqs (5) and (6) with kd = 5, α = 50 (D), kd = 50, α = 400 (E), and kd = 80, α = 400 (F). Other parameters as in Table 1. In each case, the nullclines are shown in red, the vector fields as blue arrowheads and an example trajectory in black. For the FHN equations, the diagrams show a bistable case (A), a limit cycle (B) and an excitable case (C). For Eqs (5) and (6) we present limit cycles (D, E) and an excitable case (F). For these equations, there is no bistable case.