Fig. 6.

Numerical simulation of the time series of membrane potential in neuron under different external current at $f_1=0.01,k_1=0.000085,$$I_2=0.02,f_2=0.09,k_2=0.001$, for a$I_1=0.01$; b$I_1=0.8$; c$I_1=2$ with the initial condition $\left(0,0,0,0\right)$. d present the two dimensional views of the attractor illustrating the complexity of the system when $I_1=2$