Modulation of Neural Networks for Behavior

Abstract

All animals need to shape their behavior to the demands posed by their internal and external environments. Our goal is to understand how modu­ lation of the neural networks that generate behavior occurs, so that animals can change their behavior when necessary. We discuss recent work showing that anatomical networks in the nervous system provide a physical back­ bone upon which a large library of modulatory inputs can operate. These allow the networks to produce multiple variations in output under different conditions. In the scope of this review, it is impossible to discuss all the neural circuits in which modulatory processes are now known to shape behavior (for reviews, see Selverston 1985, Harris-Warrick 1988, Kravitz 1988, Getting 1989, Bicker & Menzel 1989, Marder & Altman 1989). Instead, we have chosen examples from the literature to highlight general principles and new findings that have arisen from recent work in this field. We emphasize simple rhythmic behaviors, because more is known concerning their neural circuitry than for complex, nonrepetitive actions. As research continues, we anticipate that ideas first developed in simpler invertebrate nervous systems will be found to apply to more complex vertebrate preparations.