also known as SNIC, it is a special case bifurcation, where a stable node and a Saddle fixed point collide and annihilate on a closed invariant curve in a planar system, creating a limit cycle with an infinite period.
This is the primary mechanism for how class 1 neurons transition from a resting state to a continous periodic spiking pattern in models like Morris-Lecar Model and Hodgkin Huxley Model.
