共查询到20条相似文献,搜索用时 31 毫秒
1.
In this paper we consider the hypothesis that the spinal locomotor network controlling trunk movements has remained essentially
unchanged during the evolutionary transition from aquatic to terrestrial locomotion. The wider repertoire of axial motor patterns
expressed by amphibians would then be explained by the influence from separate limb pattern generators, added during this
evolution. This study is based on EMG data recorded in vivo from epaxial musculature in the newt Pleurodeles waltl during unrestrained swimming and walking, and on a simplified model of the lamprey spinal pattern generator for swimming.
Using computer simulations, we have examined the output generated by the lamprey model network for different input drives.
Two distinct inputs were identified which reproduced the main features of the swimming and walking motor patterns in the newt.
The swimming pattern is generated when the network receives tonic excitation with local intensity gradients near the neck
and girdle regions. To produce the walking pattern, the network must receive (in addition to a tonic excitation at the girdles)
a phasic drive which is out of phase in the neck and tail regions in relation to the middle part of the body. To fit the symmetry
of the walking pattern, however, the intersegmental connectivity of the network had to be modified by reversing the direction
of the crossed inhibitory pathways in the rostral part of the spinal cord. This study suggests that the input drive required
for the generation of the distinct walking pattern could, at least partly, be attributed to mechanosensory feedback received
by the network directly from the intraspinal stretch-receptor system. Indeed, the input drive required resembles the pattern
of activity of stretch receptors sensing the lateral bending of the trunk, as expressed during walking in urodeles. Moreover,
our results indicate that a nonuniform distribution of these stretch receptors along the trunk can explain the discontinuities
exhibited in the swimming pattern of the newt. Thus, separate limb pattern generators can influence the original network controlling
axial movements not only through a direct coupling at the central level but also via a mechanical coupling between trunk and
limbs, which in turn influences the sensory signals sent back to the network. Taken together, our findings support the hypothesis
of a phylogenetic conservatism of the spinal locomotor networks generating axial motor patterns from agnathans to amphibians.
Received: 12 October 2001 / Accepted in revised form: 16 May 2002
Correspondence to: T. Bem (e-mail: tiaza.bem@ibib.waw.pl) 相似文献
2.
A connectionist central pattern generator for the aquatic and terrestrial gaits of a simulated salamander 总被引:1,自引:0,他引:1
Ijspeert AJ 《Biological cybernetics》2001,84(5):331-348
3.
Avis H. Cohen 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1987,160(2):181-193
Summary In the lamprey,Ichthyomyzon unicuspis, the wave of activity required for normal swimming movements can be generated by a central pattern generator (CPG) residing in the spinal cord. A constant phase coupling between spinal segments can be organized by intersegmental coordinating neurons intrinsic to the cord. The rostral and caudal segmental oscillators of the CPG have different preferred frequencies when separated from each other. Therefore the system must maintain the segmental oscillators of the locomotor CPG at a single common frequency and with the proper relative timing. Using selective lesions and a split-bath, it is demonstrated that the coordinating system is comprised of at least 3 subsystems, short-axon systems in the lateral and medial tracts and a long axon system in the lateral tracts. Each alone can sustain relatively stable coordinated activity.Abbreviations
CPG
central pattern generator
-
NMDA
N-methyl-D-aspartate
-
VR
ventral root 相似文献
4.
《Zoology (Jena, Germany)》2014,117(1):48-56
The bodies of many fishes are flexible, elastic structures; if you bend them, they spring back. Therefore, they should have a resonant frequency: a bending frequency at which the output amplitude is maximized for a particular input. Previous groups have hypothesized that swimming at this resonant frequency could maximize efficiency, and that a neural circuit called the central pattern generator might be able to entrain to a mechanical resonance. However, fishes swim in water, which may potentially damp out many resonant effects. Additionally, their bodies are elongated, which means that bending can occur in complicated ways along the length of the body. We review previous studies of the mechanical properties of fish bodies, and then present new data that demonstrate complex bending properties of elongated fish bodies. Resonant peaks in amplitude exist, but there may be many of them depending on the body wavelength. Additionally, they may not correspond to the maximum swimming speed. Next, we describe experiments using a closed-loop preparation of the lamprey, in which a preparation of the spinal cord is linked to a real-time simulation of the muscle and body properties, allowing us to examine resonance entrainment as we vary the simulated resonant frequency. We find that resonance entrainment does occur, but is rare. Gain had a significant, though weak, effect, and a nonlinear muscle model produced resonance entrainment more often than a linear filter. We speculate that resonance may not be a critical effect for efficient swimming in elongate, anguilliform swimmers, though it may be more important for stiffer carangiform and thunniform fishes. 相似文献
5.
Recent recordings from spinal neurons in hatchling frog tadpoles allow their type-specific properties to be defined. Seven
main types of neuron involved in the control of swimming have been characterized. To investigate the significance of type-specific
properties, we build models of each neuron type and assemble them into a network using known connectivity between: sensory
neurons, sensory pathway interneurons, central pattern generator (CPG) interneurons and motoneurons. A single stimulus to
a sensory neuron initiates swimming where modelled neuronal and network activity parallels physiological activity. Substitution
of firing properties between neuron types shows that those of excitatory CPG interneurons are critical for stable swimming.
We suggest that type-specific neuronal properties can reflect the requirements for involvement in one particular network response
(like swimming), but may also reflect the need to participate in more than one response (like swimming and slower struggling).
Action Editor: Eberhard E. Fetz 相似文献
6.
Xenopus laevis: an ideal experimental model for studying the developmental dynamics of neural network assembly and sensory-motor computations 总被引:1,自引:0,他引:1
The amphibian Xenopus laevis represents a highly amenable model system for exploring the ontogeny of central neural networks, the functional establishment of sensory-motor transformations, and the generation of effective motor commands for complex behaviors. Specifically, the ability to employ a range of semi-intact and isolated preparations for in vitro morphophysiological experimentation has provided new insights into the developmental and integrative processes associated with the generation of locomotory behavior during changing life styles. In vitro electrophysiological studies have begun to explore the functional assembly, disassembly and dynamic plasticity of spinal pattern generating circuits as Xenopus undergoes the developmental switch from larval tail-based swimming to adult limb-based locomotion. Major advances have also been made in understanding the developmental onset of multisensory signal processing for reactive gaze and posture stabilizing reflexes during self-motion. Additionally, recent evidence from semi-intact animal and isolated CNS experiments has provided compelling evidence that in Xenopus tadpoles, predictive feed-forward signaling from the spinal locomotor pattern generator are engaged in minimizing visual disturbances during tail-based swimming. This new concept questions the traditional view of retinal image stabilization that in vertebrates has been exclusively attributed to sensory-motor transformations of body/head motion-detecting signals. Moreover, changes in visuomotor demands associated with the developmental transition in propulsive strategy from tail- to limb-based locomotion during metamorphosis presumably necessitates corresponding adaptive alterations in the intrinsic spinoextraocular coupling mechanism. Consequently, Xenopus provides a unique opportunity to address basic questions on the developmental dynamics of neural network assembly and sensory-motor computations for vertebrate motor behavior in general. 相似文献
7.
Kiemel T Gormley KM Guan L Williams TL Cohen AH 《Journal of computational neuroscience》2003,15(2):233-245
A method of estimating coupling strength between two neural oscillators based on their spikes trains (Kiemel and Cohen, J. Comput. Neurosci. 5: 267–284, 1998) is tested using simulated data and then applied to experimental data from the central pattern generator (CPG) for swimming in the lamprey. The method is tested using a model of two connectionist oscillators and a model of two endogenously bursting cells. For both models, the method provides useful estimates of the relative strength of coupling in each direction, as well as estimates of total strength. The method is applied to pairs of motor-nerve recordings from isolated 50-segment pieces of spinal cords from adult silver lampreys (Ichthyomyzon unicuspus). The strength and direction of coupling is estimated under control conditions and conditions in which intersegmental coupling between the two recording locations is weakened by hemisections of the spinal cords and/or chambers containing an inhibitory solution that blocks firing in postsynaptic cells. The relevance of these measures in constraining models of the CPG is discussed. 相似文献
8.
A traveling wave in a two-dimensional spinal cord model constitutes a stable pattern generator for quadruped gaits. In the
context of the somatotopic organization of the spinal cord, this pattern generator is sufficient to generate stable locomotive
limb trajectories. The elastic properties of muscles alone, providing linear negative feedback, are sufficient to stabilize
stance and locomotion in the presence of perturbative forces. We further show that such a pattern generator is capable of
organizing sensory processing in the spinal cord. A single-layer perceptron was trained to associate the sensory feedback
from the limb (coding force, length, and change of length for each muscle) with the two-dimensional activity profile of the
traveling wave. This resulted in a well-defined spatial organization of the connections within the spinal network along a
rostrocaudal axis. The spinal network driven by peripheral afferents alone supported autonomous locomotion in the positive
feedback mode, whereas in the negative feedback mode stance was stabilized in response to perturbations. Systematic variation
of a parameter representing the effect of gamma-motor neurons on muscle spindle activity in our model led to a corresponding
shift of limb position during stance and locomotion, resulting in a systematic displacement alteration of foot positions.
Received: 30 July 2001 / Accepted in revised form: 17 April 2002
Correspondence to: A. Kaske (e-mails: alexander.kaske@mtc.ki.se, alexander.kaske@vglab.com) 相似文献
9.
Associative neural network model for the generation of temporal patterns. Theory and application to central pattern generators. 总被引:2,自引:1,他引:2
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cyclic patterns of motor neuron activity are involved in the production of many rhythmic movements, such as walking, swimming, and scratching. These movements are controlled by neural circuits referred to as central pattern generators (CPGs). Some of these circuits function in the absence of both internal pacemakers and external feedback. We describe an associative neural network model whose dynamic behavior is similar to that of CPGs. The theory predicts the strength of all possible connections between pairs of neurons on the basis of the outputs of the CPG. It also allows the mean operating levels of the neurons to be deduced from the measured synaptic strengths between the pairs of neurons. We apply our theory to the CPG controlling escape swimming in the mollusk Tritonia diomedea. The basic rhythmic behavior is shown to be consistent with a simplified model that approximates neurons as threshold units and slow synaptic responses as elementary time delays. The model we describe may have relevance to other fixed action behaviors, as well as to the learning, recall, and recognition of temporally ordered information. 相似文献
10.
The spinal neural networks of larval zebrafish (Danio rerio) generate a variety of movements such as escape, struggling, and swimming. Various mechanisms at the neural and network levels have been proposed to account for switches between these behaviors. However, there are currently no detailed demonstrations of such mechanisms. This makes determining which mechanisms are plausible extremely difficult. In this paper, we propose a detailed biologically plausible model of the interactions between the swimming and escape networks in the larval zebrafish, while taking into account anatomical and physiological evidence. We show that the results of our neural model generate the expected behavior when used to control a hydrodynamic model of carangiform locomotion. As a result, the model presented here is a clear demonstration of a plausible mechanism by which these distinct behaviors can be controlled. Interestingly, the networks are anatomically overlapping, despite clear differences in behavioral function and physiology. 相似文献
11.
12.
U. Bässler 《Biological cybernetics》1986,54(1):65-69
A central pattern generator (CPG) is defined here as a neural network responsible for the production of the timing cues of a rhythmic motor output pattern in the isolated CNS. For the intact animal, model considerations show that this term is neither clearly delimited from the concept of a reflex chain nor from the concept of a pattern generator with functional principles different from those of the CPG. Therefore, it cannot be concluded from the existence of a CPG in the isolated nervous system that this CPG also provides the decisive timing cues in the intact animal. Consequences for the study of the neural basis of rhythmic movements are shown. 相似文献
13.
A Bionic Neural Network for Fish-Robot Locomotion 总被引:1,自引:0,他引:1
Dai-bing Zhang De-wen Hu Lin-cheng Shen Hai-bin Xie 《仿生工程学报(英文版)》2006,3(4):187-194
A bionic neural network for fish-robot locomotion is presented. The bionic neural network inspired from fish neural net- work consists of one high level controller and one chain of central pattern generators (CPGs). Each CPG contains a nonlinear neural Zhang oscillator which shows properties similar to sine-cosine model. Simulation re, suits show that the bionic neural network presents a good performance in controlling the fish-robot to execute various motions such as startup, stop, forward swimming, backward swimming, turn right and turn left. 相似文献
14.
Iman Kamali Sarvestani Alexander Kozlov Nalin Harischandra Sten Grillner Örjan Ekeberg 《Biological cybernetics》2013,107(5):497-512
This study addresses mechanisms for the generation and selection of visual behaviors in anamniotes. To demonstrate the function of these mechanisms, we have constructed an experimental platform where a simulated animal swims around in a virtual environment containing visually detectable objects. The simulated animal moves as a result of simulated mechanical forces between the water and its body. The undulations of the body are generated by contraction of simulated muscles attached to realistic body components. Muscles are driven by simulated motoneurons within networks of central pattern generators. Reticulospinal neurons, which drive the spinal pattern generators, are in turn driven directly and indirectly by visuomotor centers in the brainstem. The neural networks representing visuomotor centers receive sensory input from a simplified retina. The model also includes major components of the basal ganglia, as these are hypothesized to be key components in behavior selection. We have hypothesized that sensorimotor transformation in tectum and pretectum transforms the place-coded retinal information into rate-coded turning commands in the reticulospinal neurons via a recruitment network mimicking the layered structure of tectal areas. Via engagement of the basal ganglia, the system proves to be capable of selecting among several possible responses, even if exposed to conflicting stimuli. The anatomically based structure of the control system makes it possible to disconnect different neural components, yielding concrete predictions of how animals with corresponding lesions would behave. The model confirms that the neural networks identified in the lamprey are capable of responding appropriately to simple, multiple, and conflicting stimuli. 相似文献
15.
In this paper, we present a model for the development of connections between muscle afferents and motoneurones in the human spinal cord. The model consists of a limb with six muscles, one motoneurone pool, one pooled (Ia-like) afferent for each muscle and a central programme generator. The weights of the connections between the afferents and the motoneurone pools are adapted during centrally induced movements of the limb. The connections between the afferents and the motoneurone pools adapt in a hebbian way, using only local information present at the synapses. This neural network is tested in two examples of a limb with two degrees of freedom and six muscles. Despite the simplifications, the model predicts the pattern of autogenic and heterogenic monosynaptic reflexes quite realistically. 相似文献
16.
Kahn JA Roberts A 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1982,296(1081):229-243
The central nervous system of paralysed Xenopus laevis embryos can generate a motor output pattern suitable for swimming locomotion. By recording motor root activity in paralysed embryos with transected nervous systems we have shown that: (a) the spinal cord is capable of swimming pattern generation; (b) swimming pattern generator capability in the hindbrain and spinal cord is distributed; (c) caudal hindbrain is necessary for sustained swimming output after discrete stimulation. By recording similarly from embryos whose central nervous system was divided longitudinally into left and right sides, we have shown that: (a) each side can generate rhythmic motor output with cycle periods like those in swimming; (b) during this activity cycle period increases within an episode, and there is the usual rostrocaudal delay found in swimming; (c) this activity is influenced by sensory stimuli in the same way as swimming activity; (d) normal phase coupling of the left and right sides can be established by the ventral commissure in the spinal cord. We conclude that interactions between the antagonistic (left and right) motor systems are not necessary for swimming rhythm generation and present a model for swimming pattern generation where autonomous rhythm generators on each side of the nervous system drive the motoneurons. Alternation is achieved by reciprocal inhibition, and activity is initiated and maintained by tonic excitation from the hindbrain. 相似文献
17.
Modulation of swimming speed in the pteropod mollusc,Clione limacina: Role of a compartmental serotonergic system 总被引:6,自引:0,他引:6
In locomotory systems, the central pattern generator and motoneuron output must be modulated in order to achieve variability in locomotory speed, particularly when speed changes are important components of different behavior acts. The swimming system of the pteropod molluscClione limacina is an excellent model system for investigating such modulation. In particular, a system of central serotonergic neurons has been shown to be intimately involved in regulating output of the locomotory pattern generator and motor system ofClione. There are approximately 27 pairs of serotonin-immunoreactive neurons in the central nervous system ofClione, with about 75% of these identified. The majority of these identified immunoreactive neurons are involved in various aspects of locomotory speed modulation. A symmetrical cluster of pedal serotonergic neurons serves to increase wing contractility without affecting wing-beat frequency or motoneuron activity. Two clusters of cerebral cells produce widespread responses that lead to an increase in pattern generator cycle frequency, recruitment of swim motoneurons, activation of the pedal serotonergic neurons and excitation of the heart excitor neuron. A pair of ventral cerebral neurons provides weak excitatory inputs to the swimming system, and strongly inhibits neurons of the competing whole-body withdrawal network. Overall, the serotonergic system inClione is compartmentalized so that each subsystem (usually neuron cluster) can act independently or in concert to produce variability in locomotory speed. 相似文献
18.
F.-Y. Zhao A. Roberts 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,183(6):753-758
This paper investigates the proposal that the frequency of the swimming central pattern generator in young Xenopus tadpoles is partly determined by the population of glutamatergic premotor interneurons active on each cycle. During fictive
swimming spinal neurons also receive cholinergic and electrotonic excitation from motoneurons. As frequency changes during
swimming we make two predictions: first, since most motoneurons fire very reliably at all frequencies, the electrotonic and
nicotinic drive from motoneurons should remain constant, and second, when swimming frequency decreases, the glutamatergic
drive should decrease as the number of active premotor excitatory interneurons decreases. We have tested these predictions
by measuring the excitatory synaptic drive to motoneurons as frequency changes during fictive swimming. The components of
synaptic drive were revealed by the local microperfusion of strychnine together with different excitatory antagonists. After
blocking the nicotinic acetylcholine receptor, the mainly glutmatergic excitatory synaptic drive still changed with frequency.
However, when glutamate receptors or all chemical transmission was blocked, excitation did not change with frequency. Our
predictions are confirmed, suggesting that premotor excitatory interneurons are a major factor in frequency control in the
tadpole central pattern generator and that motoneurons provide a stable background excitation.
Accepted: 14 August 1998 相似文献
19.
The pteropod mollusc, Clione limacina, swims by alternate dorsal–ventral flapping movements of its wing-like parapodia. The basic swim rhythm is produced by a network of pedal swim interneurons that comprise a swim central pattern generator (CPG). Serotonergic modulation of both intrinsic cellular properties of the swim interneurons and network properties contribute to swim acceleration, the latter including recruitment of type 12 interneurons into the CPG. Here we address the role of the type 12 interneurons in swim acceleration. A single type 12 interneuron is found in each of the pleural ganglia, which contributes to fast swimming by exciting the dorsal swim interneurons while simultaneously inhibiting the ventral swim interneurons. Each type 12 interneuron sends a single process through the pleural–pedal connective that branches in both ipsilateral and contralateral pedal ganglia. This anatomical arrangement allowed us to manipulate the influence of the type 12 interneurons on the swim circuitry by cutting the pleural–pedal connective followed by a “culture” period of 48 h. The mean swim frequency of cut preparations was reduced by 19% when compared to the swim frequency of uncut preparations when stimulated with 10−6 M serotonin; however, this decrease was not statistically significant. Additional evidence suggests that the type 12 interneurons may produce a short-term, immediate effect on swim acceleration while slower, modulatory inputs are taking shape. 相似文献
20.
Little is known about the role of the hindbrain during development of spinal network activity. We set out to identify the activity patterns of reticulospinal (RS) neurons of the hindbrain in fictively swimming (paralyzed) zebrafish larvae. Simultaneous recordings of RS neurons and spinal motoneurons revealed that these were coactive during spontaneous fictive swim episodes. We characterized four types of RS activity patterns during fictive swimming: (i) a spontaneous pattern of discharges resembling evoked high-frequency spiking during startle responses to touch stimuli, (ii) a rhythmic pattern of excitatory postsynaptic potentials (EPSPs) whose frequency was similar to the motoneuron EPSP frequency during swim episodes, (iii) an arrhythmic pattern consisting of tonic firing throughout swim episodes, and (iv) RS cell activity uncorrelated with motoneuron activity. Despite lesions to the rostral spinal cord that prevented ascending spinal axons from entering the hindbrain (normally starting at approximately 20 h), RS neurons continued to display the aforementioned activity patterns at day 3. However, removal of the caudal portion of the hindbrain prior to the descent of RS axons left the spinal cord network unable to generate the rhythmic oscillations normally elicited by application of N-methyl-d-aspartate (NMDA), but in approximately 40% of cases chronic incubation in NMDA maintained rhythmic activity. We conclude that there is an autonomous embryonic hindbrain network that is necessary for proper development of the spinal central pattern generator, and that the hindbrain network can partially develop independently of ascending input. 相似文献