http://www.sciencedirect.com/science/article/pii/S0960982201005814
- DOI: 10.1016/S0960-9822(01)00581-4
- Under an Elsevier user license
Open Archive
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.
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.
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