Emergent oscillations in evolutionary simulations: oscillating networks increase switching efficacy.

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].