共查询到20条相似文献,搜索用时 31 毫秒
1.
Michael Small Hugh P. C. Robinson Ingo C. Kleppe Chi Kong Tse 《Journal of mathematical biology》2010,61(4):501-526
Individual cortical synapses are known to exhibit a very complex short-time dynamic behaviour in response to simple “naturalistic”
stimulation. We describe a computational study of the experimentally obtained excitatory post-synaptic potential trains of
individual cortical synapses. By adopting a new nonlinear modelling scheme we construct robust and repeatable models of the
underlying dynamics. These models suggest that cortical synapses exhibit a wide range of either periodic or chaotic dynamics.
For stimulus at a fixed rate our models predict that the response of the individual synapse will vary from a fixed point to
periodic and chaotic, depending on the frequency of stimulus. Dynamics for individual synapses vary widely, suggesting that
the individual behaviour of synapses is highly tuned and that the dynamic behaviour of even a small network of synapse-coupled
neurons could be extremely varied. 相似文献
2.
We discuss a method by which the dynamics of a network of neurons, coupled by mutual inhibition, can be reduced to a one-dimensional
map. This network consists of a pair of neurons, one of which is an endogenous burster, and the other excitable but not bursting
in the absence of phasic input. The latter cell has more than one slow process. The reduction uses the standard separation
of slow/fast processes; it also uses information about how the dynamics on the slow manifold evolve after a finite amount
of slow time. From this reduction we obtain a one-dimensional map dependent on the parameters of the original biophysical
equations. In some parameter regimes, one can deduce that the original equations have solutions in which the active phase
of the originally excitable cell is constant from burst to burst, while in other parameter regimes it is not. The existence
or absence of this kind of regulation corresponds to qualitatively different dynamics in the one-dimensional map. The computations
associated with the reduction and the analysis of the dynamics includes the use of coordinates that parameterize by time along
trajectories, and “singular Poincaré maps” that combine information about flows along a slow manifold with information about
jumps between branches of the slow manifold.
Received: 19 May 1997 / Revised version: 6 April 1998 相似文献
3.
J. Wilson White 《Theoretical Ecology》2011,4(3):357-370
All else being equal, inversely density-dependent (IDD) mortality destabilizes population dynamics. However, stability has
not been investigated for cases in which multiple types of density dependence act simultaneously. To determine whether IDD
mortality can destabilize populations that are otherwise regulated by directly density-dependent (DDD) mortality, I used scale
transition approximations to model populations with IDD mortality at smaller “aggregation” scales and DDD mortality at larger
“landscape” scales, a pattern observed in some reef fish and insect populations. I evaluated dynamic stability for a range
of demographic parameter values, including the degree of compensation in DDD mortality and the degree of spatial aggregation,
which together determine the relative importance of DDD and IDD processes. When aggregation-scale survival was a monotonically
increasing function of density (a “dilution” effect), dynamics were stable except for extremely high levels of aggregation
combined with either undercompensatory landscape-scale density dependence or certain values of adult fecundity. When aggregation-scale
survival was a unimodal function of density (representing both “dilution” and predator “detection” effects), instability occurred
with lower levels of aggregation and also depended on the values of fecundity, survivorship, detection effect, and DDD compensation
parameters. These results suggest that only in extreme circumstances will IDD mortality destabilize dynamics when DDD mortality
is also present, so IDD processes may not affect the stability of many populations in which they are observed. Model results
were evaluated in the context of reef fish, but a similar framework may be appropriate for a diverse range of species that
experience opposing patterns of density dependence across spatial scales. 相似文献
4.
Hirokazu Toju 《Ecological Research》2011,26(2):239-251
Organisms are surrounded by their predators, parasites, hosts, and mutualists, being involved in reciprocal adaptation processes
with such “biotic environment”. The concept of “coevolution”, therefore, provides a basis for the comprehensive understanding
of evolutionary and ecological dynamics in biological communities and ecosystems. Recent studies have shown that coevolutionary
processes are spatially heterogeneous and that traits mediating interspecific interactions can evolve rapidly in natural communities.
Here, I discuss factors promoting the geographic differentiation of coevolutionary interactions, the spatial scales of the
geographic structuring, and the pace of coevolutionary changes, reviewing findings in the arms race coevolution involving
a long-mouthed weevil and its host camellia plant. Evolutionary, ecological, and population genetic studies on the system
illuminated that viewpoints from the aspect of “coevolving biosphere” were important for predicting how ongoing anthropogenic
change in global environment alter the spatiotemporal dynamics of biological communities. 相似文献
5.
Damian O. Elias Bruce R. Land Andrew C. Mason Ronald R. Hoy 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2006,192(8):799-800
Animals emit visual signals that involve simultaneous, sequential movements of appendages that unfold with varying dynamics in time and space. Algorithms have been recently reported (e.g. Peters et al. in Anim Behav 64:131–146, 2002) that enable quantitative characterization of movements as optical flow patterns. For decades, acoustical signals have been rendered by techniques that decompose sound into amplitude, time, and spectral components. Using an optic-flow algorithm we examined visual courtship behaviours of jumping spiders and depict their complex visual signals as “speed waveform”, “speed surface”, and “speed waterfall” plots analogous to acoustic waveforms, spectrograms, and waterfall plots, respectively. In addition, these “speed profiles” are compatible with analytical techniques developed for auditory analysis. Using examples from the jumping spider Habronattus pugillis we show that we can statistically differentiate displays of different “sky island” populations supporting previous work on diversification. We also examined visual displays from the jumping spider Habronattus dossenus and show that distinct seismic components of vibratory displays are produced concurrently with statistically distinct motion signals. Given that dynamic visual signals are common, from insects to birds to mammals, we propose that optical-flow algorithms and the analyses described here will be useful for many researchers.Damian O. Elias and Bruce R. Land contributed equallyAn erratum to this article can be found at 相似文献
6.
Ion channels are fundamental molecules in the nervous system that catalyze the flux of ions across the cell membrane. Ion
channel flux activity is comparable to the catalytic activity of enzyme molecules. Saturating concentrations of substrate
induce “dynamic disorder” in the kinetic rate processes of single-enzyme molecules and consequently, develop correlative “memory”
of the previous history of activities. Similarly, binding of ions as substrate alone or in presence of agonists affects the
catalytic turnover of single-ion channels. Here, we investigated the possible existence of dynamic disorder and molecular
memory in the single human-TREK1-channel due to binding of substrate/agonist using the excised inside–out patch-clamp technique.
Our results suggest that the single-hTREK1-channel behaves as a typical Michaelis–Menten enzyme molecule with a high-affinity
binding site for K+ ion as substrate. But, in contrast to enzyme, dynamic disorder in single-hTREK1-channel was not induced by substrate K+ binding, but required allosteric modification of the channel molecule by the agonist, trichloroethanol. In addition, interaction
of trichloroethanol with hTREK1 induced strong correlation in the waiting time and flux intensity, exemplified by distinct
mode-switching between high and low flux activities. This suggested the induction of molecular memory in the channel molecule
by the agonist, which persisted for several decades in time. Our mathematical modeling studies identified the kinetic rate
processes associated with dynamic disorder. It further revealed the presence of multiple populations of distinct conformations
that contributed to the “heterogeneity” and consequently, to the molecular memory phenomenon that we observed. 相似文献
7.
Regulation of Long-Term Plasticity Induction by the Channel and C-Terminal Domains of GluN2 Subunits
Conventional long-term potentiation (LTP) and long-term depression (LTD) are induced by different patterns of synaptic stimulation,
but both forms of synaptic modification require calcium influx through NMDA receptors (NMDARs). A prevailing model (the “calcium
hypothesis”) suggests that high postsynaptic calcium elevation results in LTP, whereas moderate elevations give rise to LTD.
Recently, additional evidence has come to suggest that differential activation of NMDAR subunits also factors in determining
which type of plasticity is induced. While the growing amount of data suggest that activation of NMDARs containing specific
GluN2 subunits plays an important role in the induction of plasticity, it remains less clear which subunit is tied to which
form of plasticity. Additionally, it remains to be determined which properties of the subunits confer upon them the ability
to differentially induce long-term plasticity. This review highlights recent studies suggesting differential roles for the
subunits, as well as findings that begin to shed light on how two similar subunits may be linked to the induction of opposing
forms of plasticity. 相似文献
8.
Inorganic polyphosphate (iPoP)—linear chains of up to hundreds of phosphate residues—is ubiquitous in nature and appears to
be involved in many different cellular processes. In Saccharomyces cerevisiae, iPoP has been detected in high concentrations, especially after transfer of phosphate-deprived cells to a high-phosphate
medium. Here, the dynamics of iPoP synthesis in yeast as a function of the growth phase as well as glucose and phosphate availability
have been investigated. To address this question, a simple, fast and novel method for the quantification of iPoP from yeast
was developed. Both the iPoP content during growth and the iPoP “overplus” were highest towards the end of the exponential
phase, when glucose became limiting. Accumulation of iPoP during growth required excess of free phosphate, while the iPoP
“overplus” was only observed after the shift from low- to high-phosphate medium. The newly developed iPoP quantification method
and the knowledge about the dynamics of iPoP content during growth made it possible to define specific growth conditions for
the analysis of iPoP levels. These experimental procedures will be essential for the large-scale analysis of various mutant
strains or the comparison of different growth conditions. 相似文献
9.
The ability to switch attention from one aspect of an object to another or in other words to switch the “attentional set”
as investigated in tasks like the “Wisconsin Card Sorting Test” is commonly referred to as cognitive flexibility. In this work we present a biophysically detailed neurodynamical model which illustrates the neuronal base of the processes
related to this cognitive flexibility. For this purpose we conducted behavioral experiments which allow the combined evaluation of different aspects of set shifting
tasks: uninstructed set shifts as investigated in Wisconsin-like tasks, effects of stimulus congruency as investigated in
Stroop-like tasks and the contribution of working memory as investigated in “Delayed-Match-to-Sample” tasks. The work describes
how general experimental findings are usable to design the architecture of a biophysical detailed though minimalistic model
with a high orientation on neurobiological findings and how, in turn, the simulations support experimental investigations.
The resulting model is able to account for experimental and individual response times and error rates and enables the switch
of attention as a system inherent model feature: The switching process suggested by the model is based on the memorization
of the visual stimuli and does not require any synaptic learning. The operation of the model thus demonstrates with at least
a high probability the neuronal dynamics underlying a key component of human behavior: the ability to adapt behavior according
to context requirements—cognitive flexibility.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Action Editor: Peter Dayan 相似文献
10.
Theodore Vo Richard Bertram Joel Tabak Martin Wechselberger 《Journal of computational neuroscience》2010,28(3):443-458
We combine bifurcation analysis with the theory of canard-induced mixed mode oscillations to investigate the dynamics of a
novel form of bursting. This bursting oscillation, which arises from a model of the electrical activity of a pituitary cell,
is characterized by small impulses or spikes riding on top of an elevated voltage plateau. Oscillations with these characteristics
have been called “pseudo-plateau bursting”. Unlike standard bursting, the subsystem of fast variables does not possess a stable
branch of periodic spiking solutions, and in the case studied here the standard fast/slow analysis provides little information
about the underlying dynamics. We demonstrate that the bursting is actually a canard-induced mixed mode oscillation, and use
canard theory to characterize the dynamics of the oscillation. We also use bifurcation analysis of the full system of equations
to extend the results of the singular analysis to the physiological regime. This demonstrates that the combination of these
two analysis techniques can be a powerful tool for understanding the pseudo-plateau bursting oscillations that arise in electrically
excitable pituitary cells and isolated pancreatic β-cells. 相似文献
11.
D. A. Brown 《Neurophysiology》2007,39(4-5):243-247
Vladimir Skok and his colleagues did much of the pioneering work on fast excitatory synaptic transmission in sympathetic ganglia
and on nicotinic acetylcholine receptors that mediate fast transmission. I and my colleagues (including Alex Selyanko, one
of Vladimir’s protégés) have studied the additional process of slow synaptic excitation that is mediated by the action of
acetylcholine on muscarinic receptors. This results primarily from the closure of “M-channels,” a subset of voltage-gated
potassium channels composed of Kv7.2 and Kv7.3 channel subunits. These channels require membrane phosphatidylinositol-4,5-bisphosphate
(PIP2) for their opening, and their closure by muscarinic receptor activation is now thought to result from the reduction in PIP2 levels that follows receptor-induced PIP2 hydrolysis. The dynamics of these two forms of synaptic excitation are compared.
Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 284–289, July–October, 2007. 相似文献
12.
We describe a novel dynamic mechanism for episodic or compound bursting oscillations, in which bursts of electrical impulses
are clustered together into episodes, separated by long silent phases. We demonstrate the mechanism for episodic bursting
using a minimal mathematical model for “phantom bursting.” Depending on the location in parameter space, this model can produce
fast, medium, or slow bursting, or in the present case, fast, slow, and episodic bursting. The episodic bursting is modestly
robust to noise and to parameter variation, and the effect that noise has on the episodic bursting pattern is quite different
from that of an alternate episodic burst mechanism in which the slow envelope is produced by metabolic oscillations. This
mechanism could account for episodic bursting produced in endocrine cells or neurons, such as pancreatic islets or gonadotropin
releasing neurons of the hypothalamus. 相似文献
13.
We have developed a firing rate network model for working memory that combines Mexican-hat-like synaptic coupling with intrinsic
or cellular dynamics that are conditionally bistable. While our approach is in the spirit of Camperi and Wang (1998) we include
a specific and plausible mechanism for the cellular bistability. Modulatory neurotransmitters are known to activate second
messenger signaling systems, and our model includes an intracellular Ca2+ handling subsystem whose dynamics depend upon the level of the second messenger inositol 1,4,5 trisphosphate (IP3). This
Ca2+ subsystem endows individual units with conditional intrinsic bistability for a range of IP3. The full “hybrid” network sustains
IP3-dependent persistent (“bump”) activity in response to a brief transient stimulus. The bump response in our hybrid model,
like that of Camperi-Wang, is resistant to noise – its position does not drift with time.
Action Editor: Upinder Bhalla 相似文献
14.
Through the use of principal components analysis of the correlation matrix between excentricity quotients of intra- and inter-individual
transitions between pairs of the 22 most frequent behaviour elements of male and female gelada baboons observed in captivity,
the total variance could be described in terms of a low number of causal factors. In intra-individual sequences the five factors
requested of the analysis explain 74 per cent of the total variance. The following intra-individual groupings were found:
(I) “autostimulation”, (II) “intensive social” versus “groom”, (III) “male sexual”, (IV) “attack” versus “sexual presentation”,
and (V) “greeting” versus “threat”. In inter-individual transitions, the five factors explain 68 per cent of the variance.
The following communicative sets were found: (1) “female-sexual releasing”, (2) “greeting and approaching releasing” versus
“groom releasing”, (3) “austostimulation releasing” versus “male-sexual releasing”, (4) “fight releasing”, and (5) “conflict”.
Mimetic induction of same acts or acts within one particular intra-individual set was frequent. 相似文献
15.
Pedersen PL 《Journal of bioenergetics and biomembranes》2007,39(1):1-12
This introductory article to the review series entitled “The Cancer Cell’s Power Plants as Promising Therapeutic Targets”
is written while more than 20 million people suffer from cancer. It summarizes strategies to destroy or prevent cancers by
targeting their energy production factories, i.e., “power plants.” All nucleated animal/human cells have two types of power
plants, i.e., systems that make the “high energy” compound ATP from ADP and P
i
. One type is “glycolysis,” the other the “mitochondria.” In contrast to most normal cells where the mitochondria are the
major ATP producers (>90%) in fueling growth, human cancers detected via Positron Emission Tomography (PET) rely on both types
of power plants. In such cancers, glycolysis may contribute nearly half the ATP even in the presence of oxygen (“Warburg effect”).
Based solely on cell energetics, this presents a challenge to identify curative agents that destroy only cancer cells as they
must destroy both of their power plants causing “necrotic cell death” and leave normal cells alone. One such agent, 3-bromopyruvate
(3-BrPA), a lactic acid analog, has been shown to inhibit both glycolytic and mitochondrial ATP production in rapidly growing
cancers (Ko et al., Cancer Letts., 173, 83–91, 2001), leave normal cells alone, and eradicate advanced cancers (19 of 19)
in a rodent model (Ko et al., Biochem. Biophys. Res. Commun., 324, 269–275, 2004). A second approach is to induce only cancer
cells to undergo “apoptotic cell death.” Here, mitochondria release cell death inducing factors (e.g., cytochrome c). In a
third approach, cancer cells are induced to die by both apoptotic and necrotic events. In summary, much effort is being focused
on identifying agents that induce “necrotic,” “apoptotic” or apoptotic plus necrotic cell death only in cancer cells. Regardless
how death is inflicted, every cancer cell must die, be it fast or slow. 相似文献
16.
Meeta Rani 《Journal of biosciences》1998,23(1):47-54
Protein sequences of the SWISS-PROT data bank were analysed by fractal techniques and harmonic analysis. In both cases, the
results show the presence of self-affinity, a kind of self-similarity, in the sequences. Self-similarity is a sign of fractality
and fractality is a consequence of a chaotic dynamical process. The evolution of the protein sequences is modelled as a dynamical
system. The abundance of the fractal form in biology and creation of fractal forms as a result of “chaos” is already established.
It may be noted that the word “chaos” here implies that most predictable processes can also become unpredictable under certain
conditions, and that the most unpredictable processes are not as unpredictable as they are expected to be. In evolutionary
dynamics, this allows scope for mutations and variations in otherwise predictable situations, potentially leading to increased
diversity.
Part of this work was presented at the National Symposium on Evolution of Life. 相似文献
17.
Synaptic strength can be modified by the relative timing of pre- and postsynaptic activity, a phenomenon termed spike timing-dependent
plasticity (STDP). Studies of neurons in the hippocampus and in other regions have found that when presynaptic activity occurs
within a narrow time window, typically 10 or 20 ms, before postsynaptic activity, long-term potentiation (LTP) is induced,
while if presynaptic activity occurs within a similar time window after postsynaptic activity, long-term depression (LTD)
results. The mechanisms underlying these modifications are not completely understood, although there is strong evidence that
the postsynaptic Ca 2 + concentration plays a central role. Some previous modeling of STDP has focused on the dynamics of the postsynaptic Ca 2 + concentration, while other work has studied biophysical mechanisms of how a synapse can exist in, and switch between, different
states corresponding to LTP and LTD. Building on previous work in these two areas we have developed the first low level STDP
model of a tristable biochemical system that incorporates induction and maintenance of both LTP and LTD. Our model is able
to explain the STDP observed in hippocampal neurons in response to pre- and postsynaptic pulse pairs, using only parameters
derived from previous work and without the need for parameter fine-tuning. Our results also give insight into how and why
the time course of the postsynaptic Ca 2 + concentration can lead to either LTP or LTD, and suggest that voltage dependent calcium channels play a key role. 相似文献
18.
T. Matsuura S. Gorti T. Tanaka Yoshiaki Hara Mototsugu Saishin 《European biophysics journal : EBJ》1999,28(5):357-368
From observations of the dynamics of light scattered by the cornea, intensity autocorrelation func-tions that revealed two
independent diffusion coefficients, D (fast) = 2.4±0.2×10–7 cm2/s and D (slow) = 9.4±1.3× 10–9 cm2/s, were obtained. The diffusion coefficients were found to be statistically independent of the position and depth on the
lateral surface of the cornea from which the scattered light was sampled. The slow diffusion coefficients obtained from light
sampled from within cross-sections of the cornea were, however, measurably different. Diffusion coefficients obtained independently
from observations of the kinetics of corneal swelling for comparison were found to be several orders of magnitude greater
than those obtained from light scattering. The large disparity in the diffusion coefficients obtained from the two independent
methods invoked the possibility that the lamellar layers within the cornea behave as individual gel sheets. Irrespective of
this additional hypothesis, divergent behavior in the measured total scattered light intensities and diffusion coefficients
upon varying external conditions, such as temperature or pressure (stretching), was observed. Namely, a slowing down of the
dynamic modes accompanied by increased “static” scattered light intensities was observed. Although the slowing down of the
dynamic modes is possibly indicative of the reduced affinity of protein binding to the gel matrix that “softens” the gel,
the divergent behavior in the scattered light intensities and diffusion coefficients is, however, more characteristic of a
phase transition. In addition, the divergent behavior in the scattered light intensities and diffusion coefficients was reversible
up to a critical temperature (∼55 °C) or stretching (∼16%).
Received: 18 March 1998 / Revised version: 4 February 1999 / Accepted: 4 February 1999 相似文献
19.
José Antonio Villacorta-Atienza Manuel G. Velarde Valeri A. Makarov 《Biological cybernetics》2010,103(4):285-297
Animals for survival in complex, time-evolving environments can estimate in a “single parallel run” the fitness of different
alternatives. Understanding of how the brain makes an effective compact internal representation (CIR) of such dynamic situations
is a challenging problem. We propose an artificial neural network capable of creating CIRs of dynamic situations describing
the behavior of a mobile agent in an environment with moving obstacles. The network exploits in a mental world model the principle
of causality, which enables reduction of the time-dependent structure of real situations to compact static patterns. It is
achieved through two concurrent processes. First, a wavefront representing the agent’s virtual present interacts with mobile
and immobile obstacles forming static effective obstacles in the network space. The dynamics of the corresponding neurons
in the virtual past is frozen. Then the diffusion-like process relaxes the remaining neurons to a stable steady state, i.e.,
a CIR is given by a single point in the multidimensional phase space. Such CIRs can be unfolded into real space for execution
of motor actions, which allows a flexible task-dependent path planning in realistic time-evolving environments. Besides, the
proposed network can also work as a part of “autonomous thinking”, i.e., some mental situations can be supplied for evaluation
without direct motor execution. Finally we hypothesize the existence of a specific neuronal population responsible for detection
of possible time-space coincidences of the animal and moving obstacles. 相似文献
20.
Analyzing the dynamics of cellular immune responses, although performed for decades in immunologic research, has seen an enormous
increase in the number of studies using this approach since the development of intravital 2-photon microscopy. Meanwhile,
new insights into the dynamics of cellular immunity are being published on a daily basis. This review gives a short overview
of the currently most widely used techniques, both on the microscopy side as well as on the experimental part. Difficulties
and promises will be discussed. Finally, a personal selection of the most interesting findings of the first 6 years of intravital
2-photon microscopy for immunological questions will be given. The overall aim is to get the reader interested into this fascinating
way of investigating the immune response by means of “dynamic histology”. This already has and will continue to broaden our
view on how immune cells work in real life. 相似文献