Fig 1. Period-6 bursting of isolated neuron when $V_{K2}^{shift}$ = −0.01 V.

(a) Spike trains. The peaks of the 2^nd to 6^th spikes appear at 0.2884 s, 0.4483 s, 0.61s, 0.7761s, 0.9529 s after the cycle, and the 1^st to 6^th troughs appear at 0.233 s, 0.3959 s, 0.5612 s, 0.731 s, 0.9115 s, and 1.2788 s after the cycle; (b) the trajectory of period-6 bursting (thin solid line) in (m _K2, V) plane and fast-slow variable dissection. Upper (UB, dotted line), middle (MB, dashed line), and lower (LB, bold solid line) branches of a Z-shape curve present an unstable equilibrium, saddle, and stable node of the fast subsystem. The intersection pint of MB and LB is a saddle-node (SN) bifurcation point. The upper and lower solid lines correspond to maximum (V _max) and minimum (V _min) values of the stable limit cycle of the fast subsystem. The intersection point of the limit cycle of the fast subsystem and the MB is a saddle-homoclinic (SH) point. Cycle: time delay is zero.