Central pattern generators and the control of rhythmic movements

If these exist why does spasticity override them?
http://www.sciencedirect.com/science/article/pii/S0960982201005814

• Eve Marder ,
• Dirk Bucher

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DOI: 10.1016/S0960-9822(01)00581-4

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  Open Archive

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Abstract

Central pattern generators are neuronal circuits that when activated can produce rhythmic motor patterns such as walking, breathing, flying, and swimming in the absence of sensory or descending inputs that carry specific timing information. General principles of the organization of these circuits and their control by higher brain centers have come from the study of smaller circuits found in invertebrates. Recent work on vertebrates highlights the importance of neuro-modulatory control pathways in enabling spinal cord and brain stem circuits to generate meaningful motor patterns. Because rhythmic motor patterns are easily quantified and studied, central pattern generators will provide important testing grounds for understanding the effects of numerous genetic mutations on behavior. Moreover, further understanding of the modulation of spinal cord circuitry used in rhythmic behaviors should facilitate the development of new treatments to enhance recovery after spinal cord damage.

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Introduction

Biologists often take for granted the rapidity at which new information is acquired. It is humbling, therefore, to reread the papers of the first systems neuroscientists, and to discover among them the first articulation of many of the basic concepts that we still struggle to elucidate today. Almost ninety years ago, Brown [1] suggested that the alternate flexion and extension of leg muscles in walking could be produced by rhythmic central circuits in which the antagonistic muscles were driven by neurons that inhibited each other. Nonetheless, the spinal reflex has dominated a century of textbooks, and many biologists labor under the misconception that rhythmic movements are produced by reflex activation, rather than by central circuits. This review is not intended to supplant or replace the many outstanding and detailed reviews of the organization of the neural control of rhythmic movements in both invertebrates and vertebrates 2., 3., 4., 5. and 6.. Rather, here our purpose is to provide a roadmap to the general principles underlying pattern generation. We hope that this review will be helpful to those looking for neural circuits with easily quantifiable outputs with which to evaluate the role of genes in neuronal function.

Fictive motor patterns show that rhythmic movements can be generated in the absence of sensory input

How does one show the existence of central circuits capable of the production of rhythmic movements? For many years early neuroscientists debated whether rhythmic movements were produced by chains of reflexes or central oscillators (Fig. 1a). The first direct experiments designed to address this question were attempts to cut all sensory feedback to the central nervous system. This is obviously a difficult task, and some of the earliest successful experiments of this kind were carried out by Wilson and colleagues 7., 8. and 9., who showed that a deafferented locust could generate rhythmic flight motor patterns in response to non-rhythmic stimulation of the nerve cord.

Cool images at  the link.