On the transition between autonomous and nonautonomous systems: The case of FitzHugh-Nagumo's model

This work deals with a parametric linear interpolation between an autonomous FitzHugh-Nagumo model and a nonautonomous skewed problem with the same fundamental structure. This paradigmatic example allows us to construct a family of nonautonomous dynamical systems with an attracting integral manifold and a hyperbolic repelling trajectory located within the nonautonomous set enclosed by the integral manifold. Upon the variation of the parameter the integral manifold collapses, the hyperbolic repelling solution disappears and a unique globally attracting hyperbolic solution arises in what could be considered yet another pattern of nonautonomous Hopf bifurcation. Interestingly, the three phenomena do not happen at the same critical value of the parameter, yielding, thus, an example of a nonautonomous bifurcation in two steps. We provide a mathematical description of the dynamical objects at play and analyze the periodically forced case via rigorously validated continuation.