Central pattern-generating neurons and the search for general principles.
This paper selectively reviews cellular-level studies of neurons and neural networks that function to generate rhythmic physiological and behavioral events. Studies of biological rhythms during the last 75 years have modified Sherrington's concept of nervous tissue as primarily reflexive to include the fact that some neuronal activity is also endogenously rhythmic. As a functional group, neurons that initiate and maintain physiological or behavioral rhythms are referred to as central pattern generators. Comparative studies reveal a disorienting variety of biological rhythms and underlying central pattern generator control mechanisms. This paper outlines the taxonomic diversity of biological rhythms, the strengths and limitations of various models for studying central pattern generators, and the ongoing search for general principles of rhythm generation. Studies of rhythmic phenomena displayed by intact, unanesthetized mammals have been greatly enriched by data and concepts derived from invertebrate central pattern generators. This multidisciplinary influence is illustrated by reviewing recent work that aims to localize and characterize the cellular bases of circadian rhythms, reproductive rhythms, and rhythmic changes in motor control related to the sleep cycle. The paper concludes by describing studies that aim to derive a cellular-level account for oscillator interaction, sensory feedback, and the homeostatic modulation of biological rhythms.
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Department of Anesthesia, Pennsylvania State University, College of Medicine, Hershey 17033.
D000818:Animals; D002909:Chronobiology Phenomena / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D009474:Neurons / Q000502:physiology*; D012098:Reproduction / Q000502:physiology; D012890:Sleep / Q000502:physiology