Neural adaptation in the generation of rhythmic behavior

Motor systems can adapt rapidly to changes in external conditions and to sw itching of internal goals. They can also adapt slowly in response to traini ng, alterations in the mechanics of the system, and any changes in the syst em resulting from injury. This article reviews the mechanisms underlying sh ort- and long-term adaptation in rhythmic motor systems. The neuronal netwo rks underlying the generation of rhythmic motor patterns (central pattern g enerators; CPGs) are extremely flexible. Neuromodulators, central commands, and afferent signals all influence the pattern produced by a CPG by alteri ng the cellular and synaptic properties of individual neurons and the coupl ing between different populations of neurons. This flexibility allows the g eneration of a variety of motor patterns appropriate for the mechanical req uirements of different forms of a behavior. The matching of motor output to mechanical requirements depends on the capacity of pattern-generating netw orks to adapt to slow changes in body mechanics and persistent errors in pe rformance. Afferent feedback from body and limb proprioceptors likely plays an important role in driving these long-term adaptive processes.