The mammalian central pattern generator for locomotion (original) (raw)
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The mammalian central pattern generator for
2009
At the beginning of the 20th century, Thomas Graham Brown conducted experiments that after a long hiatus changed views on the neural control of locomotion. His seminal work supported by subsequent evidence generated largely from the 1960s onwards showed that across species walking, flying, and swimming are controlled largely by a neuronal network that has been referred to as the central pattern generator (CPG) for locomotion. In mammals, this caudally localized spinal cord network was found to generate the basic command signals sent to muscles of the limbs for locomotor rhythm and pattern generation. This article constitutes a comprehensive review summarizing key findings on the organization and properties of this network.
Deciphering the organization and modulation of spinal locomotor central pattern generators
Journal of Experimental Biology, 2006
SUMMARY Networks within our spinal cord generate the basic pattern underlying walking. Over the past decade, much progress has been made in our understanding of their function in a variety of vertebrate species. A significant hurdle has been the identification of candidate populations of neurons that are involved in pattern generation in the spinal cord. Recently,systems neuroscientists in collaboration with molecular biologists have begun to dissect the circuitry underlying spinal locomotor networks. These advances have combined genetic and electrophysiological techniques using in vitro preparations of the mouse spinal cord. This review will discuss new advances in the field of spinal locomotor networks with emphasis on the mouse. Many of the behaviors fundamental to animal life, such as breathing,chewing and locomotion, are rhythmic activities controlled by neuronal networks. Discerning which neurons are members of these networks, their synaptic connectivity and their individual e...
Locomotor circuits in the mammalian spinal cord
Annual Review of Neuroscience, 2006
Intrinsic spinal networks, known as central pattern generators (CPGs), control the timing and pattern of the muscle activity underlying locomotion in mammals. This review discusses new advances in understanding the mammalian CPGs with a focus on experiments that address the overall network structure as well as the identification of CPG neurons. I address the identification of excitatory CPG neurons and their role in rhythm generation, the organization of flexor-extensor networks, and the diverse role of commissural interneurons in coordinating left-right movements. Molecular and genetic approaches that have the potential to elucidate the function of populations of CPG interneurons are also discussed.
Annals of The New York Academy of Sciences, 1998
Abstract: Neuronal networks in the spinal cord are capable of producing rhythmic movements, such as walking and swimming, when the spinal cord itself is isolated from the brain and sensory inputs. These spinal networks, also called central pattern generators or CPGs, serve as relatively simple model systems for our understanding of brain functions. In this paper we concentrate on spinal CPGs in limbed vertebrates and in particular address the question: Where in the spinal cord, in the longitudinal and transverse planes, are they located? We will review the use of lesions to isolate the rhythm and pattern-generating parts of the CPG network, indirect methods like activity-dependent labeling with [14C]-2-deoxyglucose, c-fos, sulforhodamine 101, and WGA-HRP, which label presumed rhythmically active neurons en bloc, and direct methods such as calcium-imaging, extracellular and intracellular recordings, which identify rhythmically active cells directly. With this review we hope to highlight the scientific disagreements and the consensus, which have emerged from these studies with regard to the distribution of the CPG networks in the spinal cord.
Organization of mammalian locomotor rhythm and pattern generation
Brain Research Reviews, 2008
Central pattern generators (CPGs) located in the spinal cord produce the coordinated activation of flexor and extensor motoneurons during locomotion. Previously proposed architectures for the spinal locomotor CPG have included the classical half-center oscillator and the unit burst generator (UBG) comprised of multiple coupled oscillators. We have recently proposed another organization in which a two-level CPG has a common rhythm generator (RG) that controls the operation of the pattern formation (PF) circuitry responsible for motoneuron activation. These architectures are discussed in relation to recent data obtained during fictive locomotion in the decerebrate cat. The data show that the CPG can maintain the period and phase of locomotor oscillations both during spontaneous deletions of motoneuron activity and during sensory stimulation affecting motoneuron activity throughout the limb. The proposed two-level CPG organization has been investigated with a computational model which incorporates interactions between the CPG, spinal circuits and afferent inputs. The model includes interacting populations of spinal interneurons and motoneurons modeled in the Hodgkin-Huxley style. Our simulations demonstrate that a relatively simple CPG with separate RG and PF networks can realistically reproduce many experimental phenomena including spontaneous deletions of motoneuron activity and a variety of effects of afferent stimulation. The model suggests plausible explanations for a number of features of real CPG operation that would be difficult to explain in the framework of the classical single-level CPG organization. Some modeling predictions and directions for further studies of locomotor CPG organization are discussed.
Central pattern generators and the control of rhythmic movements
Current Biology, 2001
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 neuromodulatory 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.
Excitatory components of the mammalian locomotor CPG
Brain Research Reviews, 2008
Locomotion in mammals is to a large degree controlled directly by intrinsic spinal networks, called central pattern generators (CPGs). The overall function of these networks is governed by interaction between inhibitory and excitatory neurons. In the present review, we will discuss recent findings addressing the role of excitatory synaptic transmission for network function including the role of specific excitatory neuronal populations in coordinating muscle activity and in generating rhythmic activity.
2006
A computational model of the mammalian spinal cord circuitry incorporating a two-level central pattern generator (CPG) with separate half-centre rhythm generator (RG) and pattern formation (PF) networks has been developed from observations obtained during fictive locomotion in decerebrate cats. Sensory afferents have been incorporated in the model to study the effects of afferent stimulation on locomotor phase switching and step cycle period and on the firing patterns of flexor and extensor motoneurones. Here we show that this CPG structure can be integrated with reflex circuits to reproduce the reorganization of group I reflex pathways occurring during locomotion. During the extensor phase of fictive locomotion, activation of extensor muscle group I afferents increases extensor motoneurone activity and prolongs the extensor phase. This extensor phase prolongation may occur with or without a resetting of the locomotor cycle, which (according to the model) depends on the degree to which sensory input affects the RG and PF circuits, respectively. The same stimulation delivered during flexion produces a temporary resetting to extension without changing the timing of following locomotor cycles. The model reproduces this behaviour by suggesting that this sensory input influences the PF network without affecting the RG. The model also suggests that the different effects of flexor muscle nerve afferent stimulation observed experimentally (phase prolongation versus resetting) result from opposing influences of flexor group I and II afferents on the PF and RG circuits controlling the activity of flexor and extensor motoneurones. The results of modelling provide insights into proprioceptive control of locomotion.
Gait & Posture, 1998
Many studies have shown that a special treadmill training is effective in restoring locomotor function in cats with a complete spinal lesion. In the last few years it has become possible to regain some locomotor activity in patients suffering from a spinal cord injury through an intense training on a treadmill, as in cats. The ideas behind this approach owe much to insights derived from studies on spinalized animals. The neural system responsible for the locomotor restoration in both cats and humans is thought to be located at spinal level and is referred to as the central pattern generator. The evidence for such a spinal central pattern generator is reviewed in part 1. An important element in the treadmill training for both spinal injured cats and humans is the provision of adequate locomotor related sensory input, which can possibly activate and/or regulate the spinal locomotor circuitry. This part of the review deals with the afferent control of the central pattern generator. Furthermore, the results of treadmill training for both cats and humans and their relation to sensory input are treated. These insights can possibly contribute to the design of a better treadmill training program for the rehabilitation of gait in spinal cord injured patients.
Modeling the mammalian locomotor CPG: insights from mistakes and perturbations
Progress in brain research, 2007
A computational model of the mammalian spinal cord circuitry incorporating a two-level central pattern generator (CPG) with separate half-center rhythm generator (RG) and pattern formation (PF) networks is reviewed. The model consists of interacting populations of interneurons and motoneurons described in the Hodgkin-Huxley style. Locomotor rhythm generation is based on a combination of intrinsic (persistent sodium current dependent) properties of excitatory RG neurons and reciprocal inhibition between the two half-centers comprising the RG. The two-level architecture of the CPG was suggested from an analysis of deletions (spontaneous omissions of activity) and the effects of afferent stimulation on the locomotor pattern and rhythm observed during fictive locomotion in the cat. The RG controls the activity of the PF network that in turn defines the rhythmic pattern of motoneuron activity. The model produces realistic firing patterns of two antagonist motoneuron populations and gener...