dv/dt = v − v³/3 − w + I. dw/dt = (v + a − bw)/τ. The fast variable v is the membrane potential; w is a slow recovery variable. Shows resting, spiking, and oscillatory regimes depending on applied current I.
Left: phase plane with v-nullcline (cubic, orange) and w-nullcline (linear, teal). The limit cycle appears when I exceeds the Hopf bifurcation threshold. Right: v(t) and w(t) time series. Click Stimulus to inject a brief current pulse.