LeDoux [LeDoux, J. E. The emotional brain . New York: Simon & Schuster, 1996] motivated the direct route in his dual-pathway model by arguing that the ability to switch rapidly between different modes of behavior is highly adaptive. This motivation was supported by evolutionary simulations [den Dulk, P., Heerebout, B. T., & Phaf, R. H. A computational study into the evolution of dual-route dynamics for affective processing. Journal of Cognitive Neuroscience, 15, 194–208, 2003], in which foraging agents, controlled by simple inheritable neural networks, navigated an artificial world while avoiding predation. After many generations, a dual-processing architecture evolved that enabled a rapid switch to avoidance behavior when a predator appeared. We added recurrent connections to a new “context” layer in the indirect pathway to provide the agents with a working memory of previous input (i.e., a “context”). Unexpectedly, agents with oscillating networks emerged that had a much higher fitness than agents without oscillations. Oscillations seemed to have similar effects on switching speed as the dual-processing architecture, but they enhanced switching efficacy to a much larger degree. There has been much neurobiological speculation on the function, if any, of neural oscillations. These findings suggest that the facilitation of switching behavior is a likely candidate. Moreover, the strongly improved adaptation in the simulations contradicts the position that neural oscillations are merely a by-product of cell firing and have no functional value [Pareti, G., & De Palma, A. Does the brain oscillate? The dispute on neuronal synchronization. Neurological Sciences, 25, 41–47, 2004].

The evolutionary justification by LeDoux (1996) for his dual-route model of fear processing was analyzed computationally by applying genetic algorithms to artificial neural networks. The evolution was simulated of a neural network controlling an agent that gathered food in an artificial world and that was occasionally menaced by a predator. Connections could not change in the agent's “lifetime,” so there was no learning in the simulations. Only if the smells of food and predator were hard to distinguish and the fitness reflected time pressures in escaping from the predator did the type of dual processing postulated by LeDoux emerge in the surviving agents. Processing in the “quick and dirty” pathway of the fear system ensured avoidance of both predators and food, but a distinction between food and predator was made only in the long pathway. Elaborate processing inhibited the avoidance reaction and reversed it into an approach reaction to food, but strengthened the avoidance reaction to predators (and more finely tuned the direction of escape). It is suggested that “computational neuroethology” (Beer, 1990) may help constrain reasoning in evolutionary psychology, particularly when applied to specific neurobiological models, and in the future may even generate new hypotheses for cognitive neuroscience.