Evolutionary implications of neural circuit structure and function.

Recent physiological studies of neural circuits have shown that single circuits can produce more than one behavior, and that different circuits can combine to produce a single, new behavior. Because neural circuits are multifunctional and highly integrated, they are expected to evolve relatively slowly. Comparative studies of invertebrates and vertebrates have confirmed this expectation, as circuit structure and motor pattern output are generally conserved relative to peripheral morphological structures. These findings suggest that behavioral evolution may also be relatively conservative. Information about neural circuit structure and function also has implications for our understanding of morphological and brain evolution. In particular, the conserved nature of neural circuits may contribute to evolutionary change in peripheral structures, and to the gradual increase in nervous system size over evolutionary time.