Fig. 3

Phase portrait for the cortical neuron model with quadratic recovery variable, \(a=0.1\), \(\beta=\gamma=0.5\), \(v_{1}=0\), \(v_{2}=0.2\). The voltage nullcline is shown in red and that of the recovery variable in green. Left: \(I=0\), showing a stable fixed point (black filled circle), a saddle (grey filled circle) and an unstable fixed point (white filled circle). Right: \(I=0.1\), where there is an unstable fixed point (white filled circle) with a stable limit cycle (in blue) for \(C=0.01\)