Organization of mammalian locomotor rhythm and pattern generation (original) (raw)
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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...
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.
eNeuro, 2015
The organization of neural circuits that form the locomotor central pattern generator (CPG) and provide flexor-extensor and left-right coordination of neuronal activity remains largely unknown. However, significant progress has been made in the molecular/genetic identification of several types of spinal interneurons, including V0 (V0D and V0V subtypes), V1, V2a, V2b, V3, and Shox2, among others. The possible functional roles of these interneurons can be suggested from changes in the locomotor pattern generated in mutant mice lacking particular neuron types. Computational modeling of spinal circuits may complement these studies by bringing together data from different experimental studies and proposing the possible connectivity of these interneurons that may define rhythm generation, flexor-extensor interactions on each side of the cord, and commissural interactions between left and right circuits. This review focuses on the analysis of potential architectures of spinal circuits that...
The Journal of Physiology, 2007
The temporal properties of limb motoneuron bursting underlying quadrupedal locomotion were investigated in isolated spinal cord preparations (without or with brainstem attached) taken from 0 to 4-day-old rats. When activated either with differing combinations of N-methyl-D,L-aspartate, serotonin and dopamine, or by electrical stimulation of the brainstem, the spinal cord generated episodes of fictive locomotion with a constant phase relationship between cervical and lumbar ventral root bursts. Alternation occurred between ipsi-and contra-lateral flexor and extensor motor root bursts, and the cervical and lumbar locomotor networks were always active in a diagonal coordination pattern that corresponded to fictive walking. However, unlike typical locomotion in adult animals in which extensor motoneuron bursts vary more with cycle period than flexor bursts, in the isolated neonatal cord, an increase in fictive locomotor speed was associated with a decrease in the durations of both extensor and flexor bursts, at cervical and lumbar levels. To determine whether this symmetry in flexor/extensor phase durations derived from the absence of sensory feedback that is normally provided from the limbs during intact animal locomotion, EMG recordings were made from hindlimb-attached spinal cords during drug-induced locomotor-like movements. Under these conditions, the duration of extensor muscle bursts increased with cycle period, while flexor burst durations now tended to remain constant. Moreover, after a complete dorsal rhizotomy, this extensor dominant pattern was replaced by flexor and extensor muscle bursts of similar duration. In vivo and in vitro experiments were also conducted on older postnatal (P10-12) rats at an age when body-supported adult-like locomotion occurs. Here again, characteristic extensor-dominated burst patterns observed during intact treadmill locomotion were replaced by symmetrical patterns during fictive locomotion expressed by the chemically activated isolated spinal cord, further indicating that sensory inputs are normally responsible for imposing extensor biasing on otherwise symmetrically alternating extensor/flexor oscillators.
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.
Modeling Neural Control of Locomotion: Integration of Reflex Circuits with CPG
Lecture Notes in Computer Science, 2002
A model of the spinal cord neural circuitry for control of cat hindlimb movements during locomotion was developed. The neural circuitry in the spinal cord was modeled as a network of interacting neuronal modules (NMs). All neurons were modeled in Hodgkin-Huxley style. Each NM included an αmotoneuron, Renshaw, Ia and Ib interneurons, and two interneurons associated with the central pattern generator (CPG). The CPG was integrated with reflex circuits. Each three-joint hindlimb was actuated by nine one-and two-joint muscles. Our simulation allowed us to find (and hence to suggest) an architecture of network connections within and between the NMs and a schematic of feedback connections to the spinal cord neural circuitry from muscles (Ia and Ib types) and touch sensors that provided a stable locomotion with different gaits, realistic patterns of muscle activation, and kinematics of limb movements.
Modeling the Organization of Spinal Cord Neural Circuits Controlling Two-Joint Muscles
Neuromechanical Modeling of Posture and Locomotion, 2015
The activity of most motoneurons controlling one-joint muscles during locomotion are locked to either extensor or flexor phase of locomotion. In contrast, bifunctional motoneurons, controlling two-joint muscles such as posterior biceps femoris and semitendinosus (PBSt) or rectus femoris (RF), express a variety of activity patterns including firing bursts during both locomotor phases, which may depend on locomotor conditions. Although afferent feedback and supraspinal inputs significantly contribute to shaping the activity of PBSt and RF motoneurons during real locomotion, these motoneurons show complex firing patterns and variable behaviors under the conditions of fictive locomotion in the immobilized decerebrate cat, i.e., with a lack of patterned supraspinal and afferent inputs. This suggests that firing patterns of PBSt and RF motoneurons are defined by neural interactions inherent to the locomotor central pattern generator (CPG) within the spinal cord. In this study, we use computational modeling to suggest the architecture of spinal circuits representing the locomotor CPG and the connectivity pattern of spinal interneurons defining the behavior of bifunctional PBSt and RF motoneurons. The proposed model reproduces the complex firing patterns of these motoneurons during Keywords Spinal cord • Two-joint muscles • Fictive locomotion • Central pattern generator • Computational modeling Abbreviations
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...
Control of Cat Walking and Paw-Shake by a Multifunctional Central Pattern Generator
Neuromechanical Modeling of Posture and Locomotion, 2015
Central pattern generators (CPGs) are oscillatory neuronal networks controlling rhythmic motor behaviors such as swimming, walking, and breathing. Multifunctional CPGs are capable of producing multiple patterns of rhythmic activity with different periods. Here, we investigate whether two cat rhythmic motor behaviors, walking and paw-shaking, could be controlled by a single multifunctional CPG. To do this, we have created a parsimonious model of a half-center oscillator composed of two mutually inhibitory neurons. Two basic activity regimes coexist in this model: fast 10 Hz paw-shake regime and a slow 2 Hz walking regime. It is possible to switch from paw-shaking to walking with a short pulse of conductance in one neuron, and it is possible to switch from walking to paw-shaking with a longer pulse of excitatory conductance in both neurons. The paw-shake and walking rhythms generated by the CPG model were used as input to a neuromechanical model of the cat hindlimbs to simulate the corresponding rhythmic behaviors. Simulation results demonstrated that the multifunctional half-center locomotor CPG could produce movement mechanics and muscle activity patterns typical for cat walking or paw-shake responses if synaptic weights in selected spinal circuits were altered during each behavior. We propose that the selection of CPG regimes and spinal circuitry is triggered by sensory input from paw skin afferents.
The Journal of Physiology, 2012
G. Zhong and others J Physiol 590.19 interneurons during spontaneous non-resetting deletions. Motoneurons lost rhythmic synaptic drive during ipsilateral deletions. Flexor-related commissural interneurons continued to fire rhythmically during non-resetting ipsilateral flexor deletions. Deletion analysis revealed two classes of rhythmic V2a interneurons. Type I V2a interneurons retained rhythmic synaptic drive and firing during ipsilateral motor deletions, while type II V2a interneurons lost rhythmic synaptic input and fell silent during deletions. This suggests that the type I neurons are components of the RG, whereas the type II neurons are components of the PF network. We propose a computational model of the spinal locomotor CPG that reproduces our experimental results. The results may provide novel insights into the organization of spinal locomotor networks.