Figure 2

Input effects on the nullclines. The change of the nullclines upon input is illustrated in these examples. The green lines are the nullclines (5) and (6) without input crossing at point ϕ_{X = 0}. In absence of input, the system is stable in this point. Upon input the nullclines change and are depicted as blue lines, shifting the stable point to ϕ_{X > 0}. The change of the fixed point, forces the system to evolve towards the new regime. The red dashed line represents its trajectory in the phase space. The inset shows the corresponding time course of the system's output. The parameters of the simulations are: γ _Y = 1, α^X= 0, = 100, d _Y = 0.1, γ _Z = 1, β^X= 3, = 100, β^Y= 0, = 1, β^XY= 0, = 100 and d _Z = 0.1. In absence of input X = 0 and in presence of input we consider X = 1.