Fig. 10.

Bifurcation structure of the I-cell (without gamma or theta input, i.e. System (1) subject to (3) with $a=b=0$) with respect to $I_{\mathit{ton}}$ when A: $g_M=1.5$ mS/cm² and B: $g_M=0$ mS/cm². When $g_M=1.5$ mS/cm², the stable fixed point ends at a subcritical Hopf bifurcation. A family of stable limit cycles is born at a saddle-node bifurcation of cycles. There is a bistability window of $I_{\mathit{ton}}$ values such that a stable fixed point and a stable limit cycle coexist. When $g_M=0$ mS/cm², the stable fixed points terminate and a family of stable limit cycles is born at a SNIC bifurcation