Abstract
All animals need to shape their behavior to the demands posed by their
internal and external environments. Our goal is to understand how modulation 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 backbone 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.