  Systems of FitzHugh-Nagumo units with different coupling topologies are
capable of self-generating and -terminating strong deviations from their
regular dynamics that can be regarded as extreme events due to their rareness
and recurrent occurrence. Here we demonstrate the crucial role of an interior
crisis in the emergence of extreme events. In parameter space we identify this
interior crisis as the organizing center of the dynamics by employing concepts
of mixed-mode oscillations and of leaking chaotic systems. We find that extreme
events occur in certain regions in parameter space, and we show the robustness
of this phenomenon with respect to the system size.
