Symmetry in locomotor central pattern generators and animal gaits

Animal locomotion is controlled, in part, by a central pattern generator (C PG), which is an intraspinal network of neurons capable of generating a rhy thmic output(1-4). The spatio-temporal symmetries of the quadrupedal gaits walk, trot and pace(5-8) lead to plausible assumptions about the symmetries of locomotor CPGs(9-11). These assumptions imply that the CPG of a quadrup ed should consist of eight nominally identical subcircuits, arranged in an essentially unique matter. Here we apply analogous arguments to myriapod CP Gs. Analyses based on symmetry applied to these networks lead to testable p redictions, including a distinction between primary and secondary gaits, th e existence of a new primary gait called 'jump', and the occurrence of half -integer wave numbers in myriapod gaits. For bipeds, our analysis also pred icts two gaits with the out-of-phase symmetry of the walk and two gaits wit h the in-phase symmetry of the hop. We present data that support each of th ese predictions. This work suggests that symmetry can be used to infer a pl ausible dass of CPG network architectures from observed patterns of animal gaits.