For the simple reproductive behavior exhibited by female quadrupeds, the neural circuit and several genomic modules have been worked out (Drive, MIT Press, 1999). Feedback is most prominent in the hormonal mechanisms that support the behavior, whereas most of the behavioral dynamics exhibit feedforward relations. Emboldened by the success of the analysis of this simple behavior, we've enlarged the focus of our lab's work to encompass sexual arousal and generalized CNS arousal (Brain Arousal, Harvard Univ. Press, 2006). Shannon's information theoretical calculations probably apply to CNS arousal and its (universal) complementary phenomenon, habituation. We have speculated (BioEssays, August 2007) that in an animal or human at rest, CNS arousal systems live in a chaotic domain and quickly go through a phase transition to orderly dynamics as the animal or human responds. We are testing this theoretical idea with simulations of neural nets and with deep brain stimulation that raises the arousal level of a brain damaged animal.