Central Pattern Generators for Locomotion, with Special Reference to Vertebrates

There is a gap to be bridged in vertebrate neurobiology, a gap between our knowledge of cellular mechanisms and behavior. We have achieved a widely expanded knowledge of how individual neurons function, and about synaptic transmission and membrane channels. We also increasingly understand the overall organization of different patterns of behavior, which principles apply, and which parts of eNS are important. We know much about how cells in the visual cortex respond, but little about how we perceive visual images; we know much about neuronal activity in motor cortex in relation to hand move­ ments, but little about how they are actually generated. One great challenge is to bridge this gap to understand how individual eNS neurons interact to generate different patterns of behavior, or make us perceive the environment, or memorize what we experience. Invertebrate neurobiologists have had considerable success in describing somc vcry important aspects of the cellular bases of behavior, such as asso­ ciative learning in molluscs (Kandel & Schwartz 1982) and basic patterns of behavior (Getting 1983a, Bullock 1982). In this chapter we deal with one limited aspect: how the central pattern generators that control locomotion function. Although the review is general, it emphasizes the vertebrates. We try to outline not only what we know, but also what directions seem most promising for gaining insight into how the eNS controls behavior. 233