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Results for “spatiotemporal coupling”

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PubMed2003

The ontogeny of Krox-20 expression in brainstem and cerebellar neurons.

The central expression of Krox-20, a C(2)H(2)-type zinc-finger transcription factor and immediate early gene, is primarily studied in the young embryo, where it contributes to rhombomere (r) r3 and r5 development. Data regarding the cellular localization and developmental regulation of Krox-20 protein expression in brainstem neurons are lacking. Our interest in brainstem development, coupled with findings from our lab and others that demonstrate a profound impact of a Krox-20 null mutation on brainstem-mediated behaviors, led us to investigate the spatiotemporal expression of Krox-20 protein in brainstem and cerebellar neurons to gain insight into potential cellular targets of the mutation. Understanding the cellular localization of Krox-20 is important in light of studies showing the impact of immediate early gene expression on neuronal function. Krox-20 immunohistochemistry experiments were conducted on animals at embryonic days (E) 17.0 and 18.5 and postnatal days (P) 0-1, 3-4, 7, 14, 22, and adulthood. Krox-20 expression is developmentally regulated in motoneurons, somatosensory-related neurons, Purkinje cells, and components of auditory circuitry. Neurons in the ventral cochlear nucleus and inferior colliculus show a sustained Krox-20 expression. Ultrastructural data demonstrate Krox-20 expression in somata and dendrites of central neurons. Our identification of Krox-20 expressing neurons provides us a better understanding of the behavioral consequences of the mutation. Furthermore, our results suggest that Krox-20 protein has a role in the maturation of particular brainstem and cerebellar neurons and fluctuations in Krox-20 protein expression coincide with the development of circuitry underlying brainstem-mediated behaviors.

Animals↗

PubMed2002

Suppressing spatiotemporal disorder via local perturbations in an electrochemical cell.

We report experimental results depicting suppression of complex spatiotemporal dynamics under the influence of local periodic stimulations. In an experimental electrochemical system, applying a continuous forcing signal to one of the sites in an array of eight coupled oscillators, the naturally complex behavior of the remaining seven electrodes can be converted to periodic responses. The oscillations remain periodic as long as the forcing is active and revert back to exhibiting chaotic dynamics after the control is switched off. These results can also be interpreted as experimental realization of "phase-synchronization" induced via local driving in an extended system. A possible relevance to the experimentally observed calcium wave patterns is pointed out.

Journal Article↗

PubMed2002

Microsatellite diversity and genetic structure of fragmented populations of the rare, fire-dependent shrub Grevillea macleayana.

Recent habitat loss and fragmentation superimposed upon ancient patterns of population subdivision are likely to have produced low levels of neutral genetic diversity and marked genetic structure in many plant species. The genetic effects of habitat fragmentation may be most pronounced in species that form small populations, are fully self-compatible and have limited seed dispersal. However, long-lived seed banks, mobile pollinators and long adult lifespans may prevent or delay the accumulation of genetic effects. We studied a rare Australian shrub species, Grevillea macleayana (Proteaceae), that occurs in many small populations, is self-compatible and has restricted seed dispersal. However, it has a relatively long adult lifespan (c. 30 years), a long-lived seed bank that germinates after fire and is pollinated by birds that are numerous and highly mobile. These latter characteristics raise the possibility that populations in the past may have been effectively large and genetically homogeneous. Using six microsatellites, we found that G. macleayana may have relatively low within-population diversity (3.2-4.2 alleles/locus; Hexp = 0.420-0.530), significant population differentiation and moderate genetic structure (FST = 0.218) showing isolation by distance, consistent with historically low gene flow. The frequency distribution of allele sizes suggest that this geographical differentiation is being driven by mutation. We found a lack mutation-drift equilibrium in some populations that is indicative of population bottlenecks. Combined with evidence for large spatiotemporal variation of selfing rates, this suggests that fluctuating population sizes characterize the demography in this species, promoting genetic drift. We argue that natural patterns of pollen and seed dispersal, coupled with the patchy, fire-shaped distribution, may have restricted long-distance gene flow in the past.

Alleles↗

PubMed2002

Synchronization and information processing by an on-off coupling.

This paper proposes an on-off coupling process for chaos synchronization and information processing. An in depth analysis for the net effect of a conventional coupling is performed. The stability of the process is studied. We show that the proposed controlled coupling process can locally minimize the smoothness and the fidelity of dynamical data. A digital filter expression for the on-off coupling process is derived and a connection is made to the Hanning filter. The utility and robustness of the proposed approach is demonstrated by chaos synchronization in Duffing oscillators, the spatiotemporal synchronization of noisy nonlinear oscillators, the estimation of the trend of a time series, and restoration of the contaminated solution of the nonlinear Schrödinger equation.

Journal Article↗

PubMed1993

Spatiotemporal induction of immediate early genes in the rat brain after limbic seizures: effects of NMDA receptor antagonist MK-801.

Fos, jun and krox belong to multigene families coding for transcription factors. These cellular immediate early genes (IEGs) are thought to be involved in coupling neuronal excitation to changes of target gene expression. Immunocytochemistry with specific antisera was used to assess regional levels of six IEG-encoded proteins (c-Fos, Fos B, Krox-24, c-Jun, Jun B, Jun D) in the rat forebrain after kainic acid-induced limbic seizures. The results demonstrate a complex spatial pattern of IEG induction and/or suppression in limbic and non-limbic structures. The sequence of induction within hippocampal subpopulations was identical for all IEGs investigated, following the order dentate gyrus, CA1 and CA3, and irrespective of different temporal profiles for individual transcription factors. Since Fos and Jun proteins act via homo- and heterodimer complexes at specific DNA sites, our data imply that the postictal combinatorial changes of these dimers allow a sequential and differential regulation of target gene expression in specific forebrain regions. Pretreatment with the non-competitive NMDA receptor antagonist MK-801 did not affect kainate-induced expression of IEGs in the limbic system, indicating that IEG induction in these regions is mediated by high-affinity kainate and AMPA receptors rather than NMDA receptors. In contrast, MK-801 abolished IEG induction in the somatosensory cortex and striatum, suggesting that IEG expression in non-limbic neurons occurs transsynaptically and is mediated by NMDA receptors.

Animals↗

PubMed2001

What is a moment? Transient synchrony as a collective mechanism for spatiotemporal integration.

A previous paper described a network of simple integrate-and-fire neurons that contained output neurons selective for specific spatiotemporal patterns of inputs; only experimental results were described. We now present the principles behind the operation of this network and discuss how these principles point to a general class of computational operations that can be carried out easily and naturally by networks of spiking neurons. Transient synchrony of the action potentials of a group of neurons is used to signal "recognition" of a space-time pattern across the inputs of those neurons. Appropriate synaptic coupling produces synchrony when the inputs to these neurons are nearly equal, leaving the neurons unsynchronized or only weakly synchronized for other input circumstances. When the input to this system comes from timed past events represented by decaying delay activity, the pattern of synaptic connections can be set such that synchronization occurs only for selected spatiotemporal patterns. We show how the recognition is invariant to uniform time warp and uniform intensity change of the input events. The fundamental recognition event is a transient collective synchronization, representing "many neurons now agree," an event that is then detected easily by a cell with a small time constant. If such synchronization is used in neurobiological computation, its hallmark will be a brief burst of gamma-band electroencephalogram noise when and where such a recognition event or decision occurs.

Action Potentials↗

PubMed2006

Cortically coupled computer vision for rapid image search.

We describe a real-time electroencephalography (EEG)-based brain-computer interface system for triaging imagery presented using rapid serial visual presentation. A target image in a sequence of nontarget distractor images elicits in the EEG a stereotypical spatiotemporal response, which can be detected. A pattern classifier uses this response to reprioritize the image sequence, placing detected targets in the front of an image stack. We use single-trial analysis based on linear discrimination to recover spatial components that reflect differences in EEG activity evoked by target versus nontarget images. We find an optimal set of spatial weights for 59 EEG sensors within a sliding 50-ms time window. Using this simple classifier allows us to process EEG in real time. The detection accuracy across five subjects is on average 92%, i.e., in a sequence of 2500 images, resorting images based on detector output results in 92% of target images being moved from a random position in the sequence to one of the first 250 images (first 10% of the sequence). The approach leverages the highly robust and invariant object recognition capabilities of the human visual system, using single-trial EEG analysis to efficiently detect neural signatures correlated with the recognition event.

Algorithms↗

PubMed2006

Systems analysis of PKA-mediated phosphorylation gradients in live cardiac myocytes.

Compartmentation and dynamics of cAMP and PKA signaling are important determinants of specificity among cAMP's myriad cellular roles. Both cardiac inotropy and the progression of heart disease are affected by spatiotemporal variations in cAMP/PKA signaling, yet the dynamic patterns of PKA-mediated phosphorylation that influence differential responses to agonists have not been characterized. We performed live-cell imaging and systems modeling of PKA-mediated phosphorylation in neonatal cardiac myocytes in response to G-protein coupled receptor stimuli and UV photolysis of "caged" cAMP. cAMP accumulation was rate-limiting in PKA-mediated phosphorylation downstream of the beta-adrenergic receptor. Prostaglandin E1 stimulated higher PKA activity in the cytosol than at the sarcolemma, whereas isoproterenol triggered faster sarcolemmal responses than cytosolic, likely due to restricted cAMP diffusion from submembrane compartments. Localized UV photolysis of caged cAMP triggered gradients of PKA-mediated phosphorylation, enhanced by phosphodiesterase activity and PKA-mediated buffering of cAMP. These findings indicate that combining live-cell FRET imaging and mechanistic computational models can provide quantitative understanding of spatiotemporal signaling.

Animals↗

PubMed2001

Partial synchronization and spontaneous spatial ordering in coupled chaotic systems.

A model of many symmetrically and locally coupled chaotic oscillators is studied. Partial chaotic synchronizations associated with spontaneous spatial ordering are demonstrated. Very rich patterns of the system are revealed, based on partial synchronization analysis. The stabilities of different partially synchronous spatiotemporal structures and some dynamical behaviors of these states are discussed both numerically and analytically.

Journal Article↗

PubMed2001

Pattern formation on trees.

Networks having the geometry and the connectivity of trees are considered as the spatial support of spatiotemporal dynamical processes. A tree is characterized by two parameters: its ramification and its depth. The local dynamics at the nodes of a tree is described by a nonlinear map, giving rise to a coupled map lattice system. The coupling is expressed by a matrix whose eigenvectors constitute a basis on which spatial patterns on trees can be expressed by linear combination. The spectrum of eigenvalues of the coupling matrix exhibit a nonuniform distribution that manifests itself in the bifurcation structure of the spatially synchronized modes. These models may describe reaction-diffusion processes and several other phenomena occurring on heterogeneous media with hierarchical structure.

Journal Article↗

PubMed2001

Regular wave propagation out of noise in chemical active media.

A pacemaker, regularly emitting chemical waves, is created out of noise when an excitable photosensitive Belousov-Zhabotinsky medium, strictly unable to autonomously initiate autowaves, is forced with a spatiotemporal patterned random illumination. These experimental observations are also reproduced numerically by using a set of reaction-diffusion equations for an activator-inhibitor model, and further analytically interpreted in terms of genuine coupling effects arising from parametric fluctuations. Within the same framework we also address situations of noise-sustained propagation in subexcitable media.

Journal Article↗

PubMed2002

Electrotonically mediated oscillatory patterns in neuronal ensembles: an in vitro voltage-dependent dye-imaging study in the inferior olive.

Spatiotemporal profiles of ensemble subthreshold neuronal oscillation were studied in brainstem slices using high-speed voltage-sensitive dye imaging. After local electrical stimuli, the overall voltage profile demonstrated coherent oscillatory waves that spread over the inferior olive (IO). These oscillations were also observed in concurrently obtained intracellular recordings from IO neurons. Over the first few seconds after the stimuli, the optically recorded oscillations clustered into coherent groups comprising hundreds of neurons. Statistical analysis of the spatial profiles of these clusters revealed size fluctuation around stable core regions that were surrounded by a rim the diameter of which varied in time during the oscillation period. The neuronal ensemble oscillations were calcium derived and had an average frequency range of 1-7 Hz. This rhythmic response demonstrated a different spatiotemporal distribution in the presence of picrotoxin, which induced the merging of neuronal clusters into larger areas of coherent activity. The possibility that such clustering is a consequence of intrinsic oscillations in ensembles of coupled neurons was tested using mathematical modeling.

Action Potentials↗

PubMedDate not supplied

Temporal clustering analysis of cerebral blood flow activation maps measured by laser speckle contrast imaging.

Temporal and spatial orchestration of neurovascular coupling in brain neuronal activity is crucial for comprehending the mechanism of functional cerebral metabolism and pathophysiology. Laser speckle contrast imaging (LSCI) through a thinned skull over the somatosensory cortex is utilized to map the spatiotemporal characteristics of local cerebral blood flow (CBF) in anesthetized rats during sciatic nerve stimulation. The time course of signals from all spatial loci among the massive dataset is hard to analyze, especially for the thousands of images, each of which composes millions of pixels. We introduce a temporal clustering analysis (TCA) method, which is proven as an efficient method to analyze functional magnetic resonance imaging (fMRI) data in the temporal domain. The timing and location of CBF activation shows that contralateral hindlimb sensory cortical microflow is activated to increase promptly in less than 1 s after the onset of 2-s electrical stimulation and is evolved in different discrete regions. This pattern is similar but slightly elaborated from the results obtained from laser Doppler flowmetry (LDF) and fMRI. We present this combination to investigate interacting brain regions, which might lead to a better understanding of the nature of brain parcellation and effective connectivity.

Animals↗

PubMed2006

A spatiotemporal analysis of enzymatic activities associated with carbon metabolism in wild-type and mutant embryos of Arabidopsis using in situ histochemistry.

Arabidopsis as a molecular genetic model offers many advantages for the study of seed development, but these do not extend to biochemical and enzymatic studies, which are often compromised by the limited amount of material available from the small developing embryos. A set of assays based on the coupling of an enzymatic reaction to the reduction of NAD, NADP or FAD, and subsequent reduction and precipitation of a tetrazolium salt, have been adapted to investigate 18 enzyme activities associated with carbon metabolism in developing Arabidopsis embryos. The use of organelle-specific marker enzymes demonstrates the utility of the method for detection of activities in mitochondria, plastids and peroxisomes as well as the cytosol. The temporal staining patterns obtained allow classification of the activities into three main categories based on whether they peak in the early, intermediate or late stages of maturation. An interesting switch from ATP to pyrophosphate consuming pathways occurs at the onset of the maturation phase, which involves key steps in primary carbon metabolism such as phosphofructokinase. This spatiotemporal characterization of carbon metabolism has also been applied to various mutants disrupted in embryo development including gnom (gn), acetyl-CoA carboxylase1 (acc1), schlepperless (slp), and wrinkled1 (wri1). The data obtained demonstrate that the extent to which carbon metabolism is affected in mutants is not necessarily correlated to the severity of the mutation considered. Through the advanced characterization of trehalose-6-P synthase1 (tps1) embryos, this approach finally provides new insight into the regulatory role played by trehalose metabolism in embryo development.

Arabidopsis↗

PubMed1999

Corticofugal modulation of functional connectivity within the auditory thalamus of rat, guinea pig and cat revealed by cooling deactivation.

Microelectrode recordings were simultaneously performed at multiple sites in the medial geniculate body (MGB) of anesthetized cats, rats and guinea pigs. We studied the effect of cortical deactivation on the association of neural activity within the thalamus during spontaneous activity. The corticofugal influence was suppressed by temporary cooling of the auditory cortex. Pairs of spike trains recorded from the same electrode were distinguished from cases where units were in MGB but recorded with different electrodes. Time domain analyses included crosscorrelations and search for precise repetition of complex spatiotemporal firing patterns of reverberating thalamic circuits. As a complementary approach we performed bispectral analyses of simultaneously recorded local field potentials in order to uncover the frequency components of their power spectra which are non linearly coupled. All results suggest that new functional neuronal circuits might appear at the thalamic level in the absence of input from the cortex. The newly active intrathalamic connections would provide the necessary input to sustain the reverberating activity of thalamic cell assemblies and generate low frequency non-linear interactions. The dynamic control exerted by the cortex over the functional segregation of information processing carried out in the thalamus conforms with theoretical neural network studies and with the functional selectivity-adaptive filtering theory of thalamic neuronal assemblies. Although this general conclusion remains valid across species, specific differences are discussed in the frame of known differences of the microcircuitry elements.

Animals↗

PubMed2003

Simple chemomechanical process for self-generation of rhythms and forms.

We show that cross-coupling between the geometrical changes and the chemical reaction-diffusion regimes within a piece of gel embedded in a stationary reactive medium kept far from equilibrium can destabilize the trivial steady state and lead to spatiotemporal dissipative structures. The involved physical processes are the spatial bistability and the swelling properties of the gel. As an illustration of this morphogenetic process, we show that a sphere of gel immersed within such a medium with autocatalytic properties can exhibit periodic radius pulsations, the amplitude of which are controlled by chemistry.

Biomimetic Materials↗

PubMed2001

Synchronization of single-side locally averaged adaptive coupling and its application to shock capturing.

We propose a single-sided locally averaged adaptive coupling scheme for the synchronization of spatially extended systems. Coupling and synchronization are analyzed from the viewpoint of image filter construction and numerical dissipation. Single-sided locally averaged coupling is introduced based on the resolution argument of control process. Control sensors are adaptively selected and automatically adjusted according to the magnitude of local oscillations. We demonstrate that the present scheme can effectively suppress and control spatiotemporal oscillations and, thus, provide a powerful approach for shock capturing. Both the Navier-Stokes equation and Burgers' equation are used to illustrate the idea.

Journal Article↗

PubMed2004

Imaging oxygen consumption in forepaw somatosensory stimulation in rats under isoflurane anesthesia.

The cerebral metabolic rate of oxygen (CMRO2) was dynamically evaluated on a pixel-by-pixel basis in isoflurane-anesthetized and spontaneously breathing rats following graded electrical somatosensory forepaw stimulations (4, 6, and 8 mA). In contrast to alpha-chloralose, which is the most widely used anesthetic in forepaw-stimulation fMRI studies of rats under mechanical ventilation, isoflurane (1.1-1.2%) provided a stable anesthesia level over a prolonged period, without the need to adjust the ventilation volume/rate or sample blood gases. Combined cerebral blood flow signals (CBF) and blood oxygenation level-dependent (BOLD) fMRI signals were simultaneously measured with the use of a multislice continuous arterial spin labeling (CASL) technique (two-coil setup). CMRO2 was calculated using the biophysical BOLD model of Ogawa et al. (Proc Natl Acad Sci USA 1992;89:5951-5955). The stimulus-evoked BOLD percent changes at 4, 6, and 8 A were, respectively, 0.5% +/- 0.2%, 1.4% +/- 0.3%, and 2.0% +/- 0.3% (mean +/- SD, N = 6). The CBF percent changes were 23% +/- 6%, 58% +/- 9%, and 87% +/- 14%. The CMRO2 percent changes were 14% +/- 4%, 24% +/- 6%, and 43% +/- 11%. BOLD, CBF, and CMRO2 activations were localized to the forepaw somatosensory cortices without evidence of plateau for oxygen consumption, indicative of partial coupling of CBF and CMRO2. This study describes a useful forepaw-stimulation model for fMRI, and demonstrate that CMRO2 changes can be dynamically imaged on a pixel-by-pixel basis in a single setting with high spatiotemporal resolution.

Anesthetics, Inhalation↗