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Results for “spatial patterning”

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At least 757 records · Page 42Linked to original sources
PubMed1997

Spatial electrical patterns in simulated neuronal dendrites.

Steady state longitudinal distributions of (a) the density of channels conducting an inward transmembrane current of cations, (b) the submembrane concentrations of these cations, and (c) the resting membrane potential, were investigated in a phenomenological model of a cylinder-shaped dendritic process of the neuron. It was found that spatially non-uniform patterns of these distributions occur only if one of the following conditions held (i) an increase in the intracellular concentration of cations conducting an inward passive transmembrane current amplified the active efflux of those cations by the pump and attenuated their passive influx through the voltage dependent channels, with amplification of the efflux lower than attenuation of the influx; (ii) molecules of mobile channels bore a negative electrophoretic charge exposed to the intracellular space and were subject to lateral electrodiffusion in the membrane; (iii) the cations induced a further release of cations from intracellular stores. Numerical simulation studies of the membrane with Na and K channels and Na/K pumps with conditions (i) and (ii) have demonstrated the possibility of the creation of inhomogeneous patterns in the neurites. These inhomogeneous patterns are dissipative structures (DSs), and they can be spatially periodic.

Dendrites↗
PubMed1992

Configural effects constrain Fourier models of pattern discrimination.

Many models of spatial pattern discrimination assume that judgments are based on information directly available from mechanisms tuned to limited ranges of spatial frequency and orientation. We tested the validity of this assumption for spatial frequency, orientation, and contrast information in a series of complex pattern discrimination experiments. Observers discriminated between simple gratings, between gratings masked by components that differed widely in spatial frequency and/or orientation, and between patterns that presented two cues to discrimination, one in each frequency and/or orientation band. Component cues were combined either in rigid-object correspondence (e.g. both components were rotated clockwise in one pattern and counterclockwise in the other) or in opposition (e.g. in one pattern one component was rotated clockwise, the other counterclockwise; the direction of rotation was reversed for each component in the second pattern). The results demonstrate that information from tuned pathways is not always used directly in making spatial judgments, but in some cases is combined across wide regions of the Fourier domain prior to the discrimination decision. We find two distinct patterns of combination that appear to independently signal information about texture and edges. These findings provide a potential link between low-level, spatially tuned analyzers in the visual system and higher-level pattern processing mechanisms.

Adult↗
PubMed2005

Diffusion and scaling during early embryonic pattern formation.

Development of spatial patterns in multicellular organisms depends on gradients in the concentration of signaling molecules that control gene expression. In the Drosophila embryo, Bicoid (Bcd) morphogen controls cell fate along 70% of the anteroposterior axis but is translated from mRNA localized at the anterior pole. Gradients of Bcd and other morphogens are thought to arise through diffusion, but this basic assumption has never been rigorously tested in living embryos. Furthermore, because diffusion sets a relationship between length and time scales, it is hard to see how patterns of gene expression established by diffusion would scale proportionately as egg size changes during evolution. Here, we show that the motion of inert molecules through the embryo is well described by the diffusion equation on the relevant length and time scales, and that effective diffusion constants are essentially the same in closely related dipteran species with embryos of very different size. Nonetheless, patterns of gene expression in these different species scale with egg length. We show that this scaling can be traced back to scaling of the Bcd gradient itself. Our results, together with constraints imposed by the time scales of development, suggest that the mechanism for scaling is a species-specific adaptation of the Bcd lifetime.

Animals↗
PubMedDate not supplied

Migration patterns in India.

"The chief objective of the present paper is to comprehend the broad spatial patterns of internal migrations in India." Aspects considered include data constraints, the magnitude of internal migration, interstate migration, migration to rural and to urban destinations, spatial patterns, and areas of origin and destination.

Asia↗
PubMed2001

Temporal and spatial expression patterns of the CRX transcription factor and its downstream targets. Critical differences during human and mouse eye development.

Cone--rod homeobox (CRX), a paired-like homeobox transcription factor, plays a major role in photoreceptor development and maintenance of the retina. Fifteen different mutations in the CRX gene have been identified as a cause of blinding retinal dystrophy. As a step towards characterizing the underlying pathophysiology of disease, temporal and spatial gene expression patterns during human and mouse eye development were investigated for CRX and for downstream retinally expressed genes, postulated to be transactivated by CRX. We found that human CRX was expressed at 10.5 weeks post-conception (p.c.). This was significantly later than observed in mouse development. Immunocytochemistry in human retina showed that CRX protein was not detected until >4 weeks later at 15 weeks p.c., implying that it would be unable to transactivate PDEB, IRBP and arrestin, which were all expressed before 15 weeks. These data therefore eliminate CRX as the major transcriptional activator of these three genes from a wide group of retinal genes that can be transactivated by CRX in vitro. Additionally, PDEB was expressed 2 weeks before CRX whereas murine Pdeb was expressed after Crx, highlighting a potential difference for the role of PDEB in human eye development. Previous data had shown CRX expression in the adult human retina to be photoreceptor-specific; however, we demonstrate that this gene is also expressed in the inner nuclear layer (INL) of the human and mouse retina by in situ hybridization and immunocytochemistry. INL localization of murine Crx was confirmed in rd/rd,cl mice, as in this mouse model the photoreceptors are absent. We have found important differences in the temporal expression of this gene in human and mouse retina, although spatial expression of the CRX gene appears to be conserved. In addition, downstream targets of CRX in vitro might not represent in vivo function during development. These data support concerns about the extent to which we can extrapolate from rodent models regarding embryonic development and disease pathophysiology.

Animals↗
PubMed2004

GIS-supported investigation of human EHEC and cattle VTEC O157 infections in Sweden: geographical distribution, spatial variation and possible risk factors.

This article describes the spatial and temporal distribution of verotoxin-producing Escherichia coli among humans (EHEC) and cattle (VTEC) in Sweden, in order to evaluate relationships between the incidence of EHEC in humans, prevalence of VTEC O157 in livestock and agricultural structure by an ecological study. The spatial patterns of the distribution of human infections were described and compared with spatial patterns of occurrence in cattle, using a Geographic Information System (GIS). The findings implicate a concentration of human infection and cattle prevalence in the southwest of Sweden. The use of probability mapping confirmed unusual patterns of infection rates. The comparison of human and cattle infection indicated a spatial and statistical association. The correlation between variables of the agricultural structure and human EHEC incidence was high, indicating a significant statistical association of cattle and farm density with human infection. The explained variation of a multiple linear regression model was 0.56.

Adolescent↗
PubMed2001

Behavioural correlates of striatal glial fibrillary acidic protein in the 3-nitropropionic acid rat model: disturbed walking pattern and spatial orientation.

The 3-nitropropionic acid animal model is a model where excitotoxicity, mitochondrial dysfunction and oxidative stress, mechanisms common to various neurodegenerative diseases, are involved. The present study investigated whether behavioural alterations in this model were related to striatal damage. Wistar and Lewis rats were exposed to 3-nitropropionic acid and their behavioural performance (open field, walking pattern and Morris Water Maze task) was tested after the injections and after a recovery period of 3 weeks. No changes in activity were found in the open field test. Altered walking pattern was observed in the footprint analysis, although a different response was observed in the Wistar rats compared to the Lewis rats. Initially increased latency times were observed during visual discrimination learning in the Morris Water Maze task in 3-nitropropionic acid-treated Wistar rats compared to Wistar controls. During spatial discrimination learning (invisible platform) in the Morris Water Maze task the swimming velocity was decreased in both rat strains as a result of 3-nitropropionic acid treatment. Increased striatal glial fibrillary acidic protein concentration in Wistar rats correlated with several parameters of the footprint analysis and with the latency and distance in visual as well as spatial discrimination learning in the Morris Water Maze. It is concluded that measurement of walking pattern and spatial orientation performance are sensitive indicators to monitor behavioural changes in relation to striatal degeneration in the 3-nitropropionic acid animal model. In addition, Lewis rats are less sensitive towards 3-nitropropionic acid treatment than Wistar rats.

Animals↗
PubMed1996

Neighborhood Effects in Bird Distributions, Navarre, Spain

This study examines the role of neighborhood effects in the spatial distributions of selected bird species in Navarre, Spain. We employed a geographic information system (GIS) to organize the data on bird distributions and relevant environmental variables and to analyze their spatial patterns. Three bird species were selected for analysis: the European honey-buzzard (Pernis apivorus), the Eurasian hobby (Falco subbuteo), and the European pied flycatcher (Ficedula hypoleuca). Selected environmental variables of the study area were digitized to create a comprehensive data base and logistic regression models were used to evaluate the significance of each variable in the spatial distribution. The spatial patterns of bird distributions were used to extract topological relationships and to identify neighborhood effects. Although all the selected species illustrate a pattern of positive spatial autocorrelation in their distributions, the significance of neighborhood effects varies from species to species. Among the selected species, neighborhood effects are most evident in the distribution of the European pied flycatcher and are significant for the Eurasian hobby. The distribution of the European honey-buzzard is not much affected by neighborhood effects. The results suggest that examination of neighborhood effects is a prerequisite for modeling bird distributions.KEY WORDS: neighborhood effects, spatial autocorrelation, logistic regression, bird distributions.

Journal Article↗
PubMed2002

Fine temporal resolution of analytic phase reveals episodic synchronization by state transitions in gamma EEGs.

The analytic signal given by the Hilbert transform applied to an electroencephalographic (EEG) trace is a vector of instantaneous amplitude and phase at the temporal resolution of the digitizing interval (here 2 ms). The transform was applied after band-pass filtering for extracting the gamma band (20-80 Hz in rabbits) to time series from up to 64 EEG channels recorded simultaneously from high-density arrays giving spatial "windows" of 4 x 4 to 6 x 6 mm onto the visual, auditory, or somatosensory cortical surface. The time series of the analytic phase revealed phase locking for brief time segments in spatial patterns of nonzero phase values from multiple EEG that was punctuated by episodic phase decoherence. The derivative of the analytic phase revealed spikes occurring not quite simultaneously (within +/- 4 ms) across arrays aperiodically at mean rates in and below the theta range (3-7 Hz). Two measures of global synchronization over a group of channels were derived from analytic phase differences between pairs of channels on the same area of cortex. One was a synchronization index expressing phase locking. The other was a decoherence index estimating the variance in phase among multiple channels. Spectral analyses of the indices indicated that decoherence events recurred aperiodically at rates in and below the theta range of the EEGs. The results provide support for the hypothesis that neurons in mesoscopic neighborhoods in sensory cortices self-organize their activity by synaptic interactions into wave packets that have spatial patterns of amplitude (AM) and phase (PM) modulation of their spatially coherent carrier waves in the gamma range and that form and dissolve aperiodically at rates in and below the theta range. Each AM pattern is formed by a nonlinear state transition in the cortical dynamics, as shown by spikes in the derivative. Phase locking within each PM pattern is not at zero phase lag but over a fixed distribution of phase values that is consistent with the radially symmetric phase gradients already reported called "phase cones" detected by Fourier-based methods. The insight is suggested that sensory cortices are bistable comparably to cardiac dynamics, with a diastolic state that accepts sensory input and an abrupt transition to a systolic state that transmits perceptual output. Further support for this inference will require improvements in methods for temporal resolution of the times of onset of spatial patterns of phase modulation.

Animals↗
PubMed2001

Dendritic spatial flicker of local membrane potential due to channel noise and probabilistic firing of hippocampal neurons in culture.

Whole-cell recordings and imaging of dissociated hippocampal neurons stained with voltage sensitive dye provide a new microscopic picture of neuronal excitation. This is the first attempt to combine imaging of active channel clusters on the geometry of live neurons and a theoretical approach. During single somatic action potentials and the back-invasion into the neurites, local mean potentials are generated at sites of active channel clusters which are unevenly distributed in the neuronal membrane. Similar mean membrane potentials are observed in the neurites and at the soma. Identical action potentials produce different spatial patterns of mean membrane potentials from trial to trial. This spatial variability is explained by the stochastic behavior of the channels in the clusters. When hippocampal neurons are excited by synaptic inputs, their evoked responses are probabilistic and generate variable spatial patterns of mean membrane potential trial after trial. Our stochastic model reproduces this random behavior by assuming that the voltage fluctuations generated by channel noise are added to the synaptic potentials reaching the soma. We demonstrate that the probability of action potential initiation depends on the strength of the synaptic input, the diameter of the dendrites and the relative positions of the channel clusters, of the synapse and of the soma.

Action Potentials↗
PubMed2004

Spatial statistical analysis of adult mosquito (Diptera: Culicidae) counts: an example using light trap data, in Redland Shire, Southeastern Queensland, Australia.

Many mosquito control agencies use carbon dioxide-baited traps as surveillance tools for adult vector populations. However, decisions regarding the number and location of trap sites and the frequency of collections are often based on logistical issues, and not on the bionomics or spatial distribution of the target species. Therefore, with the aim of providing practical information for adult mosquito surveillance programs, we used an array of 81 carbon dioxide- and octenol-baited lights traps to obtain weekly samples of adult mosquitoes in Redland Shire in southeastern Queensland, Australia. The spatial patterns of four different mosquito species were examined, and positive spatial autocorrelation in trap counts was evident for Ochlerotatus vigilax (Skuse), Coquillettidia linealis (Skuse), and Culex annulirostris Skuse, but not for the container species Ochlerotatus notoscriptus (Skuse). Of the three species that exhibited spatially correlated trap counts, the autocorrelation was greatest in Oc. vigilax at a lag distance of 0-1.5 km, with Moran's I values of 0.30-0.64. Moran's I indices were also positive and statistically significant (P < 0.05) at lag distances of 1.5-3.0 and 3.0-4.5 km on each of the 15 sampling occasions. However, at 3.0-4.5 km the Moran's I values were low, which indicated only weak spatial autocorrelation in trap counts. Universal kriging was used to estimate the numbers of each species at unsampled locations throughout the study area, and leave-one-out cross validation analyses indicated that this was a robust method for Cq. linealis and Oc. vigilax. In contrast, trap counts for the container-breeding species Oc. notoscriptus were randomly distributed and the interpolated counts were not reliable. Comparisons of weekly contour maps of adult mosquito counts indicated a consistent spatial pattern for Oc. vigilax and Cq. linealis. Particular geographic areas had consistently high or low numbers of vectors, and these patterns were stable from year to year. Definition of geographic areas with consistently high or low numbers of vectors may allow control activities to be focused in areas with the greatest risk of arbovirus transmission.

Animals↗
PubMed1991

Genetic population structure of Italy. I. Geographic patterns of gene frequencies.

The diversity of spatial patterns of 61 allele frequencies for 20 genetic systems (15 loci) in Italy is presented. Blood antigens, enzymes, and proteins were analyzed. The total number of data points over all systems and localities was 1119. We used homogeneity tests, one-dimensional and directional spatial correlograms, and SYMAP interpolated surfaces. The data matrices were reduced by clustering techniques to reveal the principal patterns. Only a few allele frequency surfaces are strongly correlated across loci. All systems but one (ADA) exhibit significant heterogeneity in allele frequencies among the localities. Significant spatial patterns are shown by 27 of the 61 surfaces. Only one pattern (cde; system 4.19) is clinal; another (PGM1) exhibits a pure isolation by distance pattern; the others show long-range differentiation in addition to the short-distance decline of autocorrelation expected under isolation by distance. There is a marked decline in overall genetic similarity with distance for most variables. The 27 spatially significant alleles in Italy are also significantly patterned in Europe, but in all but 2 cases the country-wide and continent-wide patterns differ. The Italian patterns are due to forces specific to Italy. Differential selection for alleles associated with malaria is still evident. Whereas short-range differentiation can with malaria is still evident. Whereas short-range differentiation can be explained by isolation by distance, long-range differentiation appears to be due to demographic changes in certain populations that may be maintained by physical and linguistic isolation.

Gene Frequency↗
PubMed2005

Rapid neurotransmitter uncaging in spatially defined patterns.

Light-sensitive 'caged' molecules provide a means of rapidly and noninvasively manipulating biochemical signals with submicron spatial resolution. Here we describe a new optical system for rapid uncaging in arbitrary patterns to emulate complex neural activity. This system uses TeO(2) acousto-optical deflectors to steer an ultraviolet beam rapidly and can uncage at over 20,000 locations per second. The uncaging beam is projected into the focal plane of a two-photon microscope, allowing us to combine patterned uncaging with imaging and electrophysiology. By photolyzing caged neurotransmitter in brain slices we can generate precise, complex activity patterns for dendritic integration. The method can also be used to activate many presynaptic neurons at once. Patterned uncaging opens new vistas in the study of signal integration and plasticity in neuronal circuits and other biological systems.

Animals↗
PubMed2002

Self-organized fish schools: an examination of emergent properties.

Heterogeneous, "aggregated" patterns in the spatial distributions of individuals are almost universal across living organisms, from bacteria to higher vertebrates. Whereas specific features of aggregations are often visually striking to human eyes, a heuristic analysis based on human vision is usually not sufficient to answer fundamental questions about how and why organisms aggregate. What are the individual-level behavioral traits that give rise to these features? When qualitatively similar spatial patterns arise from purely physical mechanisms, are these patterns in organisms biologically significant, or are they simply epiphenomena that are likely characteristics of any set of interacting autonomous individuals? If specific features of spatial aggregations do confer advantages or disadvantages in the fitness of group members, how has evolution operated to shape individual behavior in balancing costs and benefits at the individual and group levels? Mathematical models of social behaviors such as schooling in fishes provide a promising avenue to address some of these questions. However, the literature on schooling models has lacked a common framework to objectively and quantitatively characterize relationships between individual-level behaviors and group-level patterns. In this paper, we briefly survey similarities and differences in behavioral algorithms and aggregation statistics among existing schooling models. We present preliminary results of our efforts to develop a modeling framework that synthesizes much of this previous work, and to identify relationships between behavioral parameters and group-level statistics.

Animals↗
PubMed2006

Adjusting neurophysiological computations in the adult olfactory bulb.

The olfactory bulb receives signals from olfactory sensory neurons and conveys them to higher centers. The mapping of the sensory inputs generates a reproducible spatial pattern in the glomerular layer of the olfactory bulb for each odorant. Then, this restricted activation is transformed into highly distributed patterns by lateral interactions between relay neurons and local interneurons. Thus, odor information processing requires the spatial patterning of both sensory inputs and synaptic interactions. In other words, odor representation is highly dynamic and temporally orchestrated. Here, we describe how the local inhibitory network shapes the global oscillations and the precise synchronization of relay neurons. We discuss how local inhibitory interneurons transpose the spatial dimension into temporal patterning. Remarkably, this transposition is not fixed but highly flexible to continuously optimize olfactory information processing.

Animals↗
PubMed2001

Evidence for two distinct mechanisms of neurogenesis and cellular pattern formation in regenerated goldfish retinas.

After its destruction by intraocular injection of ouabain, the goldfish retina regenerates, but little is known about the histogenesis of the new tissue, including the structure and formation of regenerated cell mosaic patterns. In an effort to determine how retinal cells are generated and spatially organized within retina regenerated after ouabain injection, in situ hybridization and immunocytochemical techniques were combined with computational analyses of two-dimensional spatial patterns of identified neurons. Labeling with specific opsin riboprobes revealed two distinct cone patterns in the ouabain-injected eyes, each of which was different from the relatively orderly cone patterns of native retina. Central, regenerated regions had sparse aggregates of cones, and a relatively lower density of each cone type. Peripheral regions of experimental retina, likely derived from the circumferential germinal zone, had high densities of all cone types, each of which tended to be distributed randomly. The spatial patterns of inner retinal neurons in experimental eyes were also disorganized with respect to native retina. These results indicate that although some aspects of retinal regeneration resemble normal retinal development and growth, ouabain-induced regeneration does not produce well-organized mosaics of neurons, indicating a failure of the developmental interactions needed for proper pattern formation, which in turn could compromise visual recovery. Furthermore, the distinct cone patterns in different regions of experimental retina support the hypothesis that new goldfish retina arises via two spatially and cellularly distinct mechanisms after exposure to ouabain.

Animals↗
PubMed2004

A brief visual primer for the mapping of mortality trend data.

Maps are increasingly used to visualize and analyze data, yet the spatial ramifications of data structure are rarely considered. Data are subject to transformations made throughout the research process and then used to map, visualize and conduct spatial analysis. We used mortality data to answer three research questions: Are there spatial patterns to mortality, are these patterns statistically significant, and are they persistent across time? This paper provides differential spatial patterns by implementing six data transformations: standardization, cut-points, class size, color scheme, spatial significance and temporal mapping. We use numerous maps and graphics to illustrate the iterative nature of mortality mapping, and exploit the visual nature of the International Journal of Health Geographics journal on the World Wide Web to present researchers with a series of maps.

Journal Article↗
PubMed1996

patial pattern analysis of beta-amyloid (A beta) deposits in Alzheimer disease by linear regression.

The spatial patterns of discrete beta-amyloid (Abeta) deposits in brain tissue from patients with Alzheimer disease (AD) were studied using a statistical method based on linear regression, the results being compared with the more conventional variance/mean (V/M) method. Both methods suggested that Abeta deposits occurred in clusters (400 to <12,800 mu m in diameter) in all but 1 of the 42 tissues examined. In many tissues, a regular periodicity of the Abeta deposit clusters parallel to the tissue boundary was observed. In 23 of 42 (55%) tissues, the two methods revealed essentially the same spatial patterns of Abeta deposits; in 15 of 42 (36%), the regression method indicated the presence of clusters at a scale not revealed by the V/M method; and in 4 of 42 (9%), there was no agreement between the two methods. Perceived advantages of the regression method are that there is a greater probability of detecting clustering at multiple scales, the dimension of larger Abeta clusters can be estimated more accurately, and the spacing between the clusters may be estimated. However, both methods may be useful, with the regression method providing greater resolution and the V/M method providing greater simplicity and ease of interpretation. Estimates of the distance between regularly spaced Abeta clusters were in the range 2,200-11,800 mu m, depending on tissue and cluster size. The regular periodicity of Abeta deposit clusters in many tissues would be consistent with their development in relation to clusters of neurons that give rise to specific neuronal projections.

Aged↗