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Results for “spatiotemporal coupling”

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PubMed2006

Competition between traveling fluid waves of left and right spiral vortices and their different amplitude combinations.

Stability, bifurcation properties, and the spatiotemporal behavior of different nonlinear combination structures of spiral vortices in the counterrotating Taylor-Couette system are investigated by full numerical simulations and by coupled amplitude-equation approximations. Stable cross-spiral structures with continuously varying content of left- and right-spiral modes are found. They provide a stability transferring connection between the initially stable, axially counterpropagating wave states of pure spirals and the axially standing waves of so-called ribbons that become stable slightly farther away from the onset of vortex flow.

Journal Article↗

PubMed1985

[Cerebellar cortex: simulation of recurrent collateral inhibition with the aid of a set of neuronal automata. I. Model and global results].

In view of a study on the transfer function of the cerebellar cortex a modelization of each of the various subsystems was undertaken. The recurrent collateral inhibition existing between Purkinje cells was mimicked by means of an assembly of neuronal automata (NA) temporally evolving at random through three states ("silent", "tonic" and "phasic" and interacting with simple rules. In such an assembly--by comparison with a control group of independent NA--a drastic modulation of activity appears. First the total of the mean number of state shifts is increased by more than 10%. This increase is clearly hierarchical with a maximal effect for the "silent" state. Second the average duration of each state also varies, although in a contrasted manner. Third, and moreover, a clear spatial cooperativity emerges. Indeed all the individually coupled NA are in the same "silent" state at identical moments for more than 5.5% of the total running time. A cyclic repetition of this spatiotemporal cooperativity is apparent. The emergence of these collective properties--which can not be deduced linearly from the unitary elements--introduces a parameter of order leading to a coherent functioning of the system.

Animals↗

PubMed1993

Local Lyapunov exponents for spatiotemporal chaos.

Local Lyapunov exponents are proposed for characterization of perturbations in distributed dynamical systems with chaotic behavior. Their relation to usual and velocity-dependent exponents is discussed. Local Lyapunov exponents are analytically calculated for coupled map lattices using random field approximation. Boundary Lyapunov exponents describing reflection of perturbations at boundaries are also introduced and calculated.

Journal Article↗

PubMed1994

Spatiotemporal relation between gap junctions and fascia adherens junctions during postnatal development of human ventricular myocardium.

BACKGROUND: The growing postnatal human heart maintains electromechanical function while undergoing substantial changes of cellular topology and myocardial architecture. The capacity for growth and remodeling of ventricular myocardium in adaptation to the hemodynamic changes of early infancy later declines. This decline is associated with changes in electromechanical properties of the myocardium, which suggest that the electrical and mechanical interactions between the myocytes may change in an age-dependent manner. Thus, reduction in the capacity for myocardial growth and adaptability may relate to age-dependent alterations in the patterns of the intercellular junctions that mediate electrical and mechanical coupling. We therefore examined the hypotheses that (1) age-dependent changes in the distribution patterns of gap junctions and fasciae adherentes, the intercellular junctions responsible, respectively, for electrical and mechanical coupling, accompany postnatal development in the human heart and that (2) such changes continue into the first few years of childhood. Further, the spatial relation between the two types of junction, for which a close association has been hypothesized as necessary, was explored. METHODS AND RESULTS: Ventricular myocardial gap-junction distribution was investigated in 23 pediatric surgical patients (4 weeks to 15 years old) by quantitative immunohistochemical localization of the principal cardiac gap-junctional protein, connexin43, using confocal microscopy. Immunolocalization of fascia adherens junctions by labeling N-cadherin, and correlative immunogold and standard electron microscopy, were performed in parallel. In the neonate, connexin43 gap junctions have a punctate distribution over the entire surface of the ventricular myocytes. With advancing age, gap junctions become progressively confined to the transverse terminals of the cell, ie, toward the distribution within the intercalated disk characteristic of the adult ventricle. The transversely arrayed proportion of gap-junctional label showed a linear increase with age (R = .88, P < .001), reaching the adult pattern at about 6 years, and the fascia adherens junctions showed a similar progression. Electron microscopy confirmed the changing pattern of junctional contacts and demonstrated that initially gap junctions and adhering junctions are frequently not closely adjacent but become increasingly so with maturation of the intercalated disk. CONCLUSIONS: Changes in the spatiotemporal patterns of the intercellular junctions responsible for electrical and mechanical coupling are closely coordinated in postnatal human ventricular myocardium and continue to about 6 years of age. Over this period there is a close and increasing association between the gap junctions and fascia adherens junctions. These changes in the distribution of intercellular electrical and adhering junctions may parallel the changing functional requirements of the ventricle, from a distribution that facilitates the remodeling necessitated by rapid growth and changing hemodynamics to that of the relatively stable and rapidly conducting adult myocardium. These age-related changes may also diminish the ability for appropriate myocardial remodeling in response to physiological, pathological, or surgical hemodynamic alterations.

Adolescent↗

PubMed1993

Two different spatiotemporal patterns for Ca2+ oscillations in pancreatic acinar cells: evidence of a role for protein kinase C in Ins(1,4,5)P3-mediated Ca2+ signalling.

The oscillations in cytosolic Ca2+ evoked in pancreatic exocrine acinar cells by submaximal concentrations of the two phosphoinositidase-coupled agonists acetylcholine (ACh) and cholecystokinin octapeptide (CCK-8) have very different temporal patterns. In the present study we use digital video imaging of Fura-2 fluorescence to map the spatial distribution of Ca2+ during the oscillating responses to these two agonists. The spatial patterns induced are very different for each of these agonists. ACh oscillations are sinusoidal and initiated at the secretory pole of these morphologically and functionally polarized cells. As they spread across the cell, pronounced gradients in Ca2+ develop that persist throughout the oscillating response. CCK-8 induces a series of discrete Ca2+ transients of longer duration and lower frequency. These elevations in Ca2+ arise slowly, throughout the cells and without any detectable gradients in Ca2+. We consider that the different spatiotemporal patterns can be explained on the basis of a physiologically relevant interaction between Ins(1,4,5)P3 and protein kinase C in second messenger-mediated Ca2+ signalling.

Acetylcholine↗

PubMed2004

Mechanochemical coupling of two substeps in a single myosin V motor.

Myosin V is a double-headed processive molecular motor that moves along an actin filament by taking 36-nm steps. Using optical trapping nanometry with high spatiotemporal resolution, we discovered that there are two possible pathways for the 36-nm steps, one with 12- and 24-nm substeps, in this order, and the other without substeps. Based on the analyses of effects of ATP, ADP and 2,3-butanedione 2-monoxime (a reagent shown here to slow ADP release from actomyosin V) on the dwell time and the occurrence frequency of the main and the intermediate states, we propose that the 12-nm substep occurs after ATP binding to the bound trailing head and the 24-nm substep results from a mechanical step following the isomerization of an actomyosin-ADP state on the bound leading head. When the isomerization precedes the 12-nm substep, the 36-nm step occurs without substeps.

Actins↗

PubMed2001

Spatiotemporal patterns in CO oxidation on Pt(110): the role of nonlinear diffusion.

Standing-wave patterns observed in the CO + O2 reaction on Pt(110) are described by a model that explicitly takes into account the coupling between the transport of adsorbed CO and the adsorbate-induced structural transformation of the substrate. We show that synchronization of the surface is achieved through nucleation and growth processes even in the absence of gas-phase coupling.

Journal Article↗

PubMed1993

The RF-cinematogram. A cross-correlation technique for mapping several visual receptive fields at once.

We present a spike-triggered averaging method capable of mapping the visual receptive fields of several neurons simultaneously. The stimulation is general and the mapping proceeds automatically without the need to match the stimulation to the cells' preference for position, orientation, direction, etc. The maps are spatiotemporal; receptive field (RF) structures are quantitatively determined in three dimensions: the two dimensions of visuotopic space, and time. The method presented is one of a family of "reverse correlation" or "spike-triggered averaging" techniques (DeBoer and Kuyper 1968) capable of revealing linear aspects of stimulus-response coupling. The formal relationship of these methods to stimulus-response cross-correlation is shown. The analysis is extended to provide some second-order axis-of-motion information ("direction marks"). The stimulus is a constantly illuminated, randomly jumping bright or dark spot, not an elongated bar. Spot diameters between one-third to 1 x RF width are effective. The method ascertains for each recorded action potential or "spike" the prior visual field position of the spot. The average or most probable spot positions define the receptive field spatially. Repeating the process for a succession of times prior to observed spikes defines the field temporally, presented here as a succession of spatial maps. We term this portrayal a receptive field cinematogram, RFc or ciné. The RFc reveals and economically portrays the spread of excitability and suppression across the receptive field, culminating in the generation of a spike. RFcs for LGN neurons and for simple cells recorded in cat cortical areas 17 and 18 are presented and interpreted in terms of classic ON/OFF regions. The availability of temporal information permits the separation of an excitatory exit response, generated when a moving bright spot leaves an OFF region, from an excitatory entrance response occurring when a bright spot enters an ON region, because these responses occur at different times (exit responses earlier). Spike emission remains coupled to (cross-correlated with) stimulus events over time periods as long as 96 ms, implying that some stimulus drive or afferent visual input is delayed by as much as 96 ms more than other input. This is a striking instance of temporal dispersion in the visual system. In some cells, said to be "spatiotemporally inseparable", the delay (latency) varies systematically across the visual field; i.e., the place for optimal stimulation varies with the time prior to spike emission. In these cells, the RFc shows receptive field structures which move across the visual field over trajectories equal to approximately twice the total conventional RF width.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2001

Controlling spatiotemporal chaos via phase space compression.

We present a simple and effective method for controlling spatiotemporal chaos (STC) via phase space compression, by compressing the evolution orbit of the chaotic attractor. In numerical simulations, we obtain global and local control in coupled map lattice (CML) systems by the same phase space compression in different situations, and find that the functional relationship of control results to control parameters in a certain region is the same as the local dynamics expression of the CML. According to the control equation, using different phase space compressions we successfully control a CML exhibiting STC into various desired stable states.

Journal Article↗

PubMed2006

Instability of synchronized motion in nonlocally coupled neural oscillators.

We study nonlocally coupled Hodgkin-Huxley equations with excitatory and inhibitory synaptic coupling. We investigate the linear stability of the synchronized solution, and find numerically various nonuniform oscillatory states such as chimera states, wavy states, clustering states, and spatiotemporal chaos as a result of the instability.

Action Potentials↗

PubMed2003

Ordering chaos by random shortcuts.

In this Letter, the effects of random shortcuts in an array of coupled nonlinear chaotic pendulums and their ability to control the dynamical behavior of the system are investigated. We show that random shortcuts can induce periodic synchronized spatiotemporal motions, even though all oscillators are chaotic when uncoupled. This process exhibits a nonmonotonic dependence on the density of shortcuts. Specifically, there is an optimal amount of random shortcuts, which can induce the most ordered motion characterized by the largest order parameter that is introduced to measure the spatiotemporal order. Our results imply that topological randomness can tame spatiotemporal chaos.

Journal Article↗

PubMed2005

Neural control of rhythmic sequences.

We investigated whether the temporal structure of movement sequences can be represented and learned independently of their ordinal structure, and whether some brain regions are particularly important for temporal sequence performance. Using a learning transfer design, we found evidence for independent temporal representations: learning a spatiotemporal sequence facilitated learning its temporal and ordinal structure alone; learning a temporal and an ordinal structure facilitated learning of a sequence where the two were coupled. Second, learning of temporal structures was found during reproduction of sequential stimuli with random ordinal structure, suggesting independent mechanisms for temporal learning. We then used functional magnetic resonance imaging to investigate the neural control of sequences during well-learned performance. The temporal and ordinal structures of the sequences were varied in a 2 x 2 factorial design. A dissociation was found between brain regions involved in ordinal and temporal control, the latter mainly involving the presupplementary motor area, the inferior frontal gyrus and precentral sulcus, and the superior temporal gyri. Finally, in a second fMRI experiment, well-learned temporal sequences were performed with the left or right index fingers, or using rhythmic speech. The overlap in brain activity during performance with the different effectors included a similar set of brain regions as that found in the first fMRI experiment: the supplementary motor area (SMA), the superior temporal gyrus, and the inferior frontal cortex. We thus suggest that this set of regions is important for abstract, movement-independent, temporal sequence control. This organization may be important for increased flexibility in voluntarily timed motor tasks.

Brain Mapping↗

PubMed2003

[Parkinson's disease as a model of aging: prospective analysis of gait discorders].

Falls are a dramatic consequence of the age-related gait disorders. There are few prospective studies on falls predictive of the biomechanical features of gait. According to the literature, there are similarities between the gait observed in older people and in parkinsonian subjects. The objective of this study was to apply multiparametric gait analysis to demonstrate changes of the neuromotor gait pattern connected with falls. This prospective study included two groups of 16 subjects aged more than 60 years, who had not fallen during the previous year. One group included 16 minimally disabled parkinsonian patients off drugs, and the other group 16 healthy people. Gait recordings were obtained with a three-dimensional optoelectronic movement analysis system coupled with 2 force platforms in all persons who were followed for 1 year to collect data on all new events, particularly falls. Data analysis concerned spatiotemporal stride and three-dimensional power peaks developed in each lower limb joint. Cluster analysis of the 32 persons was used to determine various infraclinic neuromotor gait patterns. A post hoc analysis of variance was then applied to identify discriminating parameters. Three groups of subjects were identified with 3 different neuromotor gait patterns, independently of the presence of Parkinson disease. There were no fallers in first group (n=18). The second group (n=8) had 20 p.cent fallers and the third group (n=4) 100 p.cent fallers. The groups differed by 4 spatiotemporal parameters and 3 joint power peaks in the sagittal plane. Functional capacity was good in the first group with no falls recorded. This group of subjects had characteristics reported in the literature corresponding to a category of persons who compensate well for the phenomena of aging. Functional capacity was intermediary in the second group (20 p. cent were fallers). The kinematic pattern appeared to be less successful, revealing a tendency for stiff posture. The third group (100 p. cent fallers) exhibited inferior functional capacity. In this group, the kinematic pattern appeared to be disrupted. The subjects were unable to adapt satisfactorily to situations other than by stereotypical neuromotor reactions. In conclusion this study demonstrated a close determinism between physiological neuromotor aging and Parkinson's disease. The prospective follow-up demonstrated that falls that occurred were related to changes in neuromotor gait patterns. Three phases of gait pattern were also identified from minimal to major risk of falls.

Aged↗

PubMed2006

Quantification of cross correlations in complex spatiotemporal systems.

We propose a design of the equal time correlation matrix suitable for the analysis of multivariate time series with ill-defined phases. We present the cross-correlation analysis of model data sets taken from coupled stochastic oscillators and compare the concept with the results obtained from a conventional correlation matrix analysis. We show that the concept provides a higher sensitivity combined with a better statistical significance when quantifying weak cross correlations.

Journal Article↗

PubMed2004

Colored conical emission by means of second harmonic generation in a quadratically nonlinear medium.

Colored conical emission was observed experimentally in a thick beta-barium borate crystal as a result of spatiotemporal modulational instability. In the presence of both dispersion and diffraction, colored conical emission showed specific features that were characteristic of the nonlinear dynamics of the strongly coupled fundamental and harmonic fields. Experimental observation directly demonstrated that beam angular spectra were substantially modified as a result of exponential growth of perturbations by means of parametric wave mixing. Seeded amplification of colored conical emission was demonstrated to support ultrabroadband up-conversion.

Journal Article↗

PubMed2002

Front initiation on microdesigned composite catalysts.

We first briefly review the subject of spatiotemporal pattern formation on microdesigned composite catalysts. One of the most significant interaction mechanisms between different reacting domains (consisting of different metal catalysts such as Pt and Rh, coupled through surface diffusion) is the initiation of reaction fronts at the interface between them. We then explore in some detail the effect of two-dimensional composite geometry on this basic building block of composite catalyst dynamics. (c) 2002 American Institute of Physics.

Journal Article↗

PubMed1999

Contributions of mitochondria to animal physiology: from homeostatic sensor to calcium signalling and cell death.

Over recent years, it has become clear that mitochondria play a central role in many key aspects of animal physiology and pathophysiology. Their central and ubiquitous task is clearly the production of ATP. Nevertheless, they also play subtle roles in glucose homeostasis, acting as the sensor for substrate supply in the transduction pathway that promotes insulin secretion by the pancreatic -cell and that modulates the excitability of the hypothalamic glucose-sensitive neurons involved in appetite control. Mitochondria may also act as sensors of availability of oxygen, the other major mitochondrial substrate, in the regulation of respiration. Mitochondria take up calcium, and the high opacity mitochondrial calcium uptake pathway provides a mechanism that couples energy demand to increased ATP production through the calcium-dependent upregulation of mitochondrial enzyme activity. Mitochondrial calcium accumulation may also have a substantial impact on the spatiotemporal dynamics of cellular calcium signals, with subtle differences of detail in different cell types. Recent work has also revealed the centrality of mitochondrial dysfunction as an irreversible step in the pathway to both necrotic and apoptotic cell death. This review looks at recent developments in these rapidly evolving areas of cell physiology in an attempt to draw together disparate areas of research into a common theme.

Animals↗

PubMedDate not supplied

Vascular smooth muscle, a multiply feedback-coupled system of high versatility, modulation and cell-signaling variability.

Under normal conditions, the various vascular regulatory effector influences are interwoven in a dynamic, and not a static, circulatory system. The reaction of a smooth muscle cell is thus reflected only incompletely by the stationary activation curve 'developed tension versus membrane potential'. The missing time domain in this relationship is a reflection of our as yet limited understanding of the system's behavior in space and time. It should be emphasized that the rhythmogenic properties of vascular smooth muscle are closely coupled to a functioning circulation. The electrical and mechanical oscillations, which can be traced back to rhythmic activity of the active, electrogenic Na+/K+ pump, could originate in the allosteric qualities of the enzyme phosphofructokinase (PFK). Thus, PFK represents a rhythmogenic enzyme which may serve as an example of the connection between the biological properties on a molecular level and the spatiotemporal system's behavior. The cardiovascular system and its rhythmicity may be dominated by only a few control points, one of which is distinguished by the viscoelastic properties of a blood flow sensor macromolecule. Therefore, the three prominent control points - PFK, (Na+ + K+)-ATPase and flow sensor conformation - acting as negatively feedback-coupled, nonlinear synergetic order parameters, are sufficient to initiate the periodic events in the cardiovascular system and to provide a plausible explanation for their causal origin.

Adenosine Triphosphate↗