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1.
M. Ullström J. Hellgren Kotaleski J. Tegnér E. Aurell S. Grillner A. Lansner 《Biological cybernetics》1998,79(1):1-14
The neuronal network underlying lamprey swimming has stimulated extensive modelling on different levels of abstraction. The
lamprey swims with a burst frequency ranging from 0.3 to 8–10 Hz with a rostro-caudal lag between bursts in each segment along
the spinal cord. The swimming motor pattern is characterized by a burst proportion that is independent of burst frequency
and lasts around 30%–40% of the cycle duration. This also applies in preparations in which the reciprocal inhibition in the
spinal cord between the left and right side is blocked. A network of coupled excitatory neurons producing hemisegmental oscillations
may form the basis of the lamprey central pattern generator (CPG). Here we explored how such networks, in principle, could
produce a large frequency range with a constant burst proportion. The computer simulations of the lamprey CPG use simplified,
graded output units that could represent populations of neurons and that exhibit adaptation. We investigated the effect of
an active modulation of the degree of adaptation of the CPG units to accomplish a constant burst proportion over the whole
frequency range when, in addition, each hemisegment is assumed to be self-oscillatory. The degree of adaptation is increased
with the degree of stimulation of the network. This will make the bursts terminate earlier at higher burst rates, allowing
for a constant burst proportion. Without modulated adaptation the network operates in a limited range of swimming frequencies
due to a progressive increase of burst duration with increasing background stimulation. By introducing a modulation of the
adaptation, a broad burst frequency range can be produced. The reciprocal inhibition is thus not the primary burst terminating
factor, as in many CPG models, and it is mainly responsible for producing alternation between the left and right sides. The
results are compared with the Morris-Lecar oscillator model with parameters set to produce a type A and type B oscillator,
in which the burst durations stay constant or increase, respectively, when the background stimulation is increased. Here as
well, burst duration can be controlled by modulation of the slow variable in a similar way as above. When oscillatory hemisegmental
networks are coupled together in a chain a phase lag is produced. The production of a phase lag in chains of such oscillators
is compared with chains of Morris-Lecar relaxation oscillators. Models relating to the intact versus isolated spinal cord
preparation are discussed, as well as the role of descending inhibition.
Received: 1 April 1997 / Accepted in revised form: 20 March 1998 相似文献
2.
B. W. Verdaasdonk H. F. J. M. Koopman F. C. T. van der Helm 《Biological cybernetics》2009,101(1):49-61
Like human walking, passive dynamic walking—i.e. walking down a slope with no actuation except gravity—is energy efficient
by exploiting the natural dynamics. In the animal world, neural oscillators termed central pattern generators (CPGs) provide
the basic rhythm for muscular activity in locomotion. We present a CPG model, which automatically tunes into the resonance
frequency of the passive dynamics of a bipedal walker, i.e. the CPG model exhibits resonance tuning behavior. Each leg is
coupled to its own CPG, controlling the hip moment of force. Resonance tuning above the endogenous frequency of the CPG—i.e.
the CPG’s eigenfrequency—is achieved by feedback of both limb angles to their corresponding CPG, while integration of the
limb angles provides resonance tuning at and below the endogenous frequency of the CPG. Feedback of the angular velocity of
both limbs to their corresponding CPG compensates for the time delay in the loop coupling each limb to its CPG. The resonance
tuning behavior of the CPG model allows the gait velocity to be controlled by a single parameter, while retaining the energy
efficiency of passive dynamic walking. 相似文献
3.
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
4.
A significant characteristic in a swimming pattern of a lamprey is the generation of a constant phase lag along its body in spite of the wide range of undulation frequencies. In this paper, we discuss a mathematical treatment for coupled oscillators with time-delayed interaction and propose a model for the central pattern generator (CPG) of a lamprey to account for the generation of a constant phase relation, with consideration of the signal conduction time. From this model, it is suggested that the desired phase relation can be produced by long ascending connections from the tail to the neck region of the CPG. 相似文献
5.
Chains of coupled limit-cycle oscillators are considered, in which the coupling is assumed to be weak and only between adjacent oscillators. For such a system the change in frequency of an oscillator due to the coupling can be expressed, up to first order in thecoupling strength, by functions that depend only on the phase difference between the coupled oscillators. In this article a numerical algorithm is developed for the evaluation of these functions (the H-functions) in terms of a single oscillator and the interactions between coupled oscillators. The technique is applied to a connectionist model for the locomotor pattern generator in the lamprey spinal cord.An H-function so derived is compared to a function derived empirically(the C-function) from simulations of the same system. The phase lagsthat develop between adjacent oscillators in a simulated chain are compared with those predicted theoretically, and it is shown that coupling thatis functionally strong is nonetheless weak enough to behave as predicted. 相似文献
6.
We investigate the temporal coordination of human gait and posture and infer the nature of their coupling. Participants viewed
a sinusoidally oscillating visual display which induced medial-lateral postural sway during treadmill walking, while display
frequency was varied (0.075–1.025 Hz). First, postural responses exhibited the usual low-pass characteristic but with an additional
resonance peak near the preferred stride frequency, although shifted downward by 0.12 Hz; this provides evidence of a coupling
from gait to posture. Second, the step cycle adapted to mode lock with the visual driver and postural sway, as well as displaying
instances of intermittency (slipping in and out of phase) and quasiperiodicity (phase wandering); this provides evidence of
a coupling from posture to gait. We observed a spectrum of integer mode locks, including a large 1:1 trapping region about
the stride frequency and superharmonic entrainment (stride frequency > driver frequency) at lower driver frequencies. A coupled-oscillator
model that incorporates a novel parametric coupling from posture to the gait “stiffness” term reproduces these features of
the data, including the resonance peak shift. Biological coordination patterns may thus emerge naturally as properties of
a system of appropriately coupled oscillators.
Received: 23 June 1999 / Accepted in revised form: 10 January 2001 相似文献
7.
We describe and analyze a model for a stochastic pulse-coupled neuronal network with many sources of randomness: random external
input, potential synaptic failure, and random connectivity topologies. We show that different classes of network topologies
give rise to qualitatively different types of synchrony: uniform (Erdős–Rényi) and “small-world” networks give rise to synchronization
phenomena similar to that in “all-to-all” networks (in which there is a sharp onset of synchrony as coupling is increased);
in contrast, in “scale-free” networks the dependence of synchrony on coupling strength is smoother. Moreover, we show that
in the uniform and small-world cases, the fine details of the network are not important in determining the synchronization
properties; this depends only on the mean connectivity. In contrast, for scale-free networks, the dynamics are significantly
affected by the fine details of the network; in particular, they are significantly affected by the local neighborhoods of
the “hubs” in the network. 相似文献
8.
Oscillators in networks may display a variety of activity patterns. This paper presents a geometric singular perturbation
analysis of clustering, or alternate firing of synchronized subgroups, among synaptically coupled oscillators. We consider
oscillators in two types of networks: mutually coupled, with all-to-all inhibitory connections, and globally inhibitory, with
one excitatory and one inhibitory population of oscillators, each of arbitrary size. Our analysis yields existence and stability
conditions for clustered states, along with formulas for the periods of such firing patterns. By using two different approaches,
we derive complementary conditions, the first set stated in terms of time lengths determined by intrinsic and synaptic properties
of the oscillators and their coupling and the second set stated in terms of model parameters and phase space structures directly
linked to parameters. These results suggest how biological components may interact to produce the spindle sleep rhythm in
thalamocortical networks.
Received: 9 September 1999 / Revised version: 7 July 2000 / Published online: 24 November 2000 相似文献
9.
Temporal correlation of neuronal activity has been suggested as a criterion for multiple object recognition. In this work,
a two-dimensional network of simplified Wilson-Cowan oscillators is used to manage the binding and segmentation problem of
a visual scene according to the connectedness Gestalt criterion. Binding is achieved via original coupling terms that link
excitatory units to both excitatory and inhibitory units of adjacent neurons. These local coupling terms are time independent,
i.e., they do not require Hebbian learning during the simulations. Segmentation is realized by a two-layer processing of the
visual image. The first layer extracts all object contours from the image by means of “retinal cells” with an “on-center”
receptive field. Information on contour is used to selectively inhibit Wilson-Cowan oscillators in the second layer, thus
realizing a strong separation among neurons in different objects. Accidental synchronism between oscillations in different
objects is prevented with the use of a global inhibitor, i.e., a global neuron that computes the overall activity in the Wilson-Cowan
network and sends back an inhibitory signal.
Simulations performed in a 50×50 neural grid with 21 different visual scenes (containing up to eight objects + background)
with random initial conditions demonstrate that the network can correctly segment objects in almost 100% of cases using a
single set of parameters, i.e., without the need to adjust parameters from one visual scene to the next. The network is robust
with reference to dynamical noise superimposed on oscillatory neurons. Moreover, the network can segment both black objects
on white background and vice versa and is able to deal with the problem of “fragmentation.”
The main limitation of the network is its sensitivity to static noise superimposed on the objects. Overcoming this problem
requires implementation of more robust mechanisms for contour enhancement in the first layer in agreement with mechanisms
actually realized in the visual cortex.
Received: 25 October 2001 / Accepted: 26 February 2003 /
Published online: 20 May 2003
Correspondence to: Mauro Ursino (e-mail: mursino@deis.unibo.it, Tel.: +39-051-2093008, Fax: +39-051-2093073) 相似文献
10.
Hard-wired central pattern generators for quadrupedal locomotion 总被引:5,自引:0,他引:5
Animal locomotion is generated and controlled, in part, by a central pattern generator (CPG), which is an intraspinal network of neurons capable of producing rhythmic output. In the present work, it is demonstrated that a hard-wired CPG model, made up of four coupled nonlinear oscillators, can produce multiple phase-locked oscillation patterns that correspond to three common quadrupedal gaits — the walk, trot, and bound. Transitions between the different gaits are generated by varying the network's driving signal and/or by altering internal oscillator parameters. The above in numero results are obtained without changing the relative strengths or the polarities of the system's synaptic interconnections, i.e., the network maintains an invariant coupling architecture. It is also shown that the ability of the hard-wired CPG network to produce and switch between multiple gait patterns is a model-independent phenomenon, i.e., it does not depend upon the detailed dynamics of the component oscillators and/or the nature of the inter-oscillator coupling. Three different neuronal oscillator models — the Stein neuronal model, the Van der Pol oscillator, and the FitzHugh-Nagumo model -and two different coupling schemes are incorporated into the network without impeding its ability to produce the three quadrupedal gaits and the aforementioned gait transitions. 相似文献
11.
We describe a simple yet general method to analyze networks of coupled identical nonlinear oscillators and study applications to fast synchronization, locomotion, and schooling. Specifically, we use nonlinear contraction theory to derive exact and global (rather than linearized) results on synchronization, antisynchronization, and oscillator death. The method can be applied to coupled networks of various structures and arbitrary size. For oscillators with positive definite diffusion coupling, it can be shown that synchronization always occurs globally for strong enough coupling strengths, and an explicit upper bound on the corresponding threshold can be computed through eigenvalue analysis. The discussion also extends to the case when network structure varies abruptly and asynchronously, as in flocks of oscillators or dynamic elements. 相似文献
12.
13.
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
14.
Protein evolution is not a random process. Views which attribute randomness to molecular change, deleterious nature to single-gene
mutations, insufficient geological time, or population size for molecular improvements to occur, or invoke “design creationism”
to account for complexity in molecular structures and biological processes, are unfounded. Scientific evidence suggests that
natural selection tinkers with molecular improvements by retaining adaptive peptide sequence. We used slot-machine probabilities
and ion channels to show biological directionality on molecular change. Because ion channels reside in the lipid bilayer of
cell membranes, their residue location must be in balance with the membrane’s hydrophobic/philic nature; a selective “pore”
for ion passage is located within the hydrophobic region. We contrasted the random generation of DNA sequence for KcsA, a
bacterial two-transmembrane-domain (2TM) potassium channel, from Streptomyces lividans, with an under-selection scenario, the “jackprot,” which predicted much faster evolution than by chance. We wrote a computer
program in JAVA APPLET version 1.0 and designed an online interface, The Jackprot Simulation
, to model a numerical interaction between mutation rate and natural selection during a scenario of polypeptide evolution.
Winning the “jackprot,” or highest-fitness complete-peptide sequence, required cumulative smaller “wins” (rewarded by selection)
at the first, second, and third positions in each of the 161 KcsA codons (“jackdons” that led to “jackacids” that led to the
“jackprot”). The “jackprot” is a didactic tool to demonstrate how mutation rate coupled with natural selection suffices to
explain the evolution of specialized proteins, such as the complex six-transmembrane (6TM) domain potassium, sodium, or calcium
channels. Ancestral DNA sequences coding for 2TM-like proteins underwent nucleotide “edition” and gene duplications to generate
the 6TMs. Ion channels are essential to the physiology of neurons, ganglia, and brains, and were crucial to the evolutionary
advent of consciousness. The Jackprot Simulation illustrates in a computer model that evolution is not and cannot be a random
process as conceived by design creationists. 相似文献
15.
Electrical transmission in the mammalian brain is now well established. A new study by Thomson and colleagues elegantly demonstrates
coupling between CA1 hippocampal pyramidal cells, which is far more common than previously supposed. Although the history
of coupling is extensive, doubt, predjudice, and technical issues long kept it from wide acceptance. Here “spikelets” or “fast
prepotentials” are found when two cells are coupled and in this situation result from electrical transmission of impulses
from one coupled cell to the other. Interesting questions remain as to whether connexin or pannexin gap junctions serve as
the molecular substrate of transmission, and the role of electrical transmission in hippocampal physiology is uncertain. Increased
coupling could well contribute to the known tendency of the hippocampus to exhibit seizure activity. 相似文献
16.
How do humans and other animals accomplish coordinated movements? How are novel combinations of limb joints rapidly assembled
into new behavioral units that move together in in-phase or anti-phase movement patterns during complex movement tasks? A
neural central pattern generator (CPG) model simulates data from human bimanual coordination tasks. As in the data, anti-phase
oscillations at low frequencies switch to in-phase oscillations at high frequencies, in-phase oscillations occur at both low
and high frequencies, phase fluctuations occur at the anti-phase in-phase transition, a “seagull effect” of larger errors
occurs at intermediate phases, and oscillations slip toward in-phase and anti-phase when driven at intermediate phases. These
oscillations and bifurcations are emergent properties of the CPG model in response to volitional inputs. The CPG model is
a version of the Ellias-Grossberg oscillator. Its neurons obey Hodgkin-Huxley type equations whose excitatory signals operate
on a faster time scale than their inhibitory signals in a recurrent on-center off-surround anatomy. When an equal command
or GO signal activates both model channels, the model CPG can generate both in-phase and anti-phase oscillations at different
GO amplitudes. Phase transitions from either in-phase to anti-phase oscillations, or from anti-phase to in-phase oscillations,
can occur in different parameter ranges, as the GO signal increases.
Received: 22 August 1994 / Accepted in revised form: 13 May 1997 相似文献
17.
A critical feature of the motor pattern generated by the lamprey spinal cord is an intersegmental delay that is constant down the cord and scales with cycle duration. This has been modelled as the output of a chain of coupled oscillators, within a general mathematical framework developed by Kopell and Ermentrout (1986, 1988). The analysis predicts that for asymmetric coupling of equally-activated oscillators, the intersegmental phase lag will be uniform along the chain except in a boundary layer at one end. Here we provide experimental evidence that a boundary layer does occur at the rostral end of an isolated preparation of lamprey spinal cord. In the context of the mathematical analysis, this indicates that ascending coupling is dominant in the control of intersegmental phase lag in the lamprey. 相似文献
18.
Systems-level modeling of neuronal circuits for leech swimming 总被引:2,自引:0,他引:2
This paper describes a mathematical model of the neuronal central pattern generator (CPG) that controls the rhythmic body
motion of the swimming leech. The systems approach is employed to capture the neuronal dynamics essential for generating coordinated oscillations of cell membrane potentials
by a simple CPG architecture with a minimal number of parameters. Based on input/output data from physiological experiments,
dynamical components (neurons and synaptic interactions) are first modeled individually and then integrated into a chain of
nonlinear oscillators to form a CPG. We show through numerical simulations that the values of a few parameters can be estimated
within physiologically reasonable ranges to achieve good fit of the data with respect to the phase, amplitude, and period.
This parameter estimation leads to predictions regarding the synaptic coupling strength and intrinsic period gradient along
the nerve cord, the latter of which agrees qualitatively with experimental observations. 相似文献
19.
B. L. Jones 《Bulletin of mathematical biology》1979,41(1):119-127
Some models for selection in enzyme coupled, selfreproducing, macromolecular systems are considered. The enzyme coupling provides
a mechanism for the buildup of systems with large information content. The concept of “selective value” and criteria for selection
is discussed. 相似文献
20.
Summary The observation of various types of spatio-temporal correlations in spike-patterns of multiple cortical neurons has shifted
attention from rate coding paradigms to computational processes based on the precise timing of spikes in neuronal ensembles.
In the present work we develop the notion of “spatial” and “temporal interaction” which provides measures for statistical
dependences in coupled stochastic processes like multiple unit spike trains. We show that the classical Willshaw network and
Abeles’ synfire chain model both reveal a moderate spatial interaction, but only the synfire chain model reveals a positive
temporal interaction, too. Systems that maximize temporal interaction are shown to be almost deterministic globally, but posses
almost unpredictable firing behavior on the single unit level. 相似文献