429373.fig.001a
(a)
429373.fig.001b
(b)
Figure 1: Tonic and reactive regulatory motifs: (a) the tonic regulatory motif maintains homeostasis by adjusting the concentration of a suppressor [S], which sets the upper bound of the activating threshold. In some cases, basal levels of an activator [R] establish the lower bound. (b) The reactive regulatory motif maintains homeostasis typically through a negative feedback loop. Negative feedback produces spiked activation and oscillations under some circumstances.