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PubMed1988

Discrete analysis of spatial-sensitivity models.

The visual representation of spatial patterns begins with a series of linear transformations: the stimulus is blurred by the optics, spatially sampled by the photoreceptor array, spatially pooled by the ganglion-cell receptive fields, and so forth. Models of human spatial-pattern vision commonly summarize the initial transformations by a single linear transformation that maps the stimulus into an array of sensor responses. Some components of the initial linear transformations (e.g., lens blurring, photoreceptor sampling) have been estimated empirically; others have not. A computable model must include some assumptions concerning the unknown components of the initial linear encoding. Even a modest sketch of the initial visual encoding requires the specification of a large number of sensors, making the calculations required for performance predictions quite large. We describe procedures for reducing the computational burden of current models of spatial vision that ensure that the simplifications are consistent with the predictions of the complete model. We also describe a method for using pattern-sensitivity measurements to estimate the initial linear transformation. The method is based on the assumption that detection performance is monotonic with the vector length of the sensor responses. We show how contrast-threshold data can be used to estimate the linear transformation needed to characterize threshold performance.

Humans↗

PubMed2001

Dual information representation with stable firing rates and chaotic spatiotemporal spike patterns in a neural network model.

Although various means of information representation in the cortex have been considered, the fundamental mechanism for such representation is not well understood. The relation between neural network dynamics and properties of information representation needs to be examined. We examined spatial pattern properties of mean firing rates and spatiotemporal spikes in an interconnected spiking neural network model. We found that whereas the spatiotemporal spike patterns are chaotic and unstable, the spatial patterns of mean firing rates (SPMFR) are steady and stable, reflecting the internal structure of synaptic weights. Interestingly, the chaotic instability contributes to fast stabilization of the SPMFR. Findings suggest that there are two types of network dynamics behind neuronal spiking: internally-driven dynamics and externally driven dynamics. When the internally driven dynamics dominate, spikes are relatively more chaotic and independent of external inputs; the SPMFR are steady and stable. When the externally driven dynamics dominate, the spiking patterns are relatively more dependent on the spatiotemporal structure of external inputs. These emergent properties of information representation imply that the brain may adopt a dual coding system. Recent experimental data suggest that internally driven and externally driven dynamics coexist and work together in the cortex.

Action Potentials↗

PubMed2002

Characterization of soil organic matter content of two sample size populations along a climatic transect.

Soil organic matter (SOM) content was determined in two populations of soil samples that were taken from 0-2 soil depth. One population represented soil samples that were taken from a square of 25 cm2 in size (small-S population) and the other population represented soil samples that were taken from a square of 2500 cm2 in size (large-L population). The samples were collected on hillslopes in different climatic regions: Mediterranean (GIV), semi-arid (MAL), mildly-arid (MIS) and arid (KAL). The results of both S and L populations showed decreasing SOM mean and variance from the Mediterranean site to the arid site. Statistical and spatial characteristics of each population were compared between the climatic regions. In addition, comparison between the two populations was made for each site. The difference in sample size did not significantly affect the mean values of SOM of the two populations in sites GIV, MAL and KAL, but did affect the mean at site MIS. At all study sites, except for site MAL, the variance increased with decreasing sample size. At sites GIV and KAL the coefficient of variation of S population was higher (more than 1.5 times) than that of L population, whereas at sites MAL and MIS, the differences were negligible. The relationships between the values of S and L samples at the individual sampling points defined the background of the study sites, which reflects the effect of vegetation (type), grazing, biological crust and soil properties. It was found that at the extreme sites GIV and KAL the background was characterized by relatively low SOM content with small areas of high organic matter content. At site MIS the background was characterized by relatively high SOM with small areas of low organic matter content. At site MAL the background was not dominated by high values of SOM nor by low ones. The spatial pattern of L population became more simple with increasing aridity. At the relatively wet sites the spatial pattern did not depend on the sample size while in the more arid sites it was sample size dependent. It was indicated that the spatial structure of SOM at the semi-arid and mildly arid sites is anisotropic whereas at the Mediterranean and arid sites it is isotropic.

Climate↗

PubMedDate not supplied

Differences in the density and spatial distribution of florid and diffuse plaques in variant Creutzfeldt-Jakob disease (vCJD).

OBJECTIVE: To determine whether in cases of variant Creutzfeldt-Jakob disease (vCJD), the florid-type plaques are derived from the diffuse plaques or whether the 2 plaque types develop independently. MATERIAL: Blocks of frontal, parietal, occipital and temporal neocortex and cerebellar cortex from 11 cases of vCJD. METHOD: The density, distribution and spatial pattern of the florid and diffuse plaques were determined in each brain region using spatial pattern analysis. RESULTS: The density of the diffuse plaques was significantly greater than that of the florid plaques in most areas. The ratio of the diffuse to florid plaques varied between brain regions and was maximal in the molecular layer of the cerebellum. The densities of the florid and diffuse plaques were positively correlated in the parietal cortex, occipital cortex, the inferior temporal gyrus and the dentate gyrus. Plaque densities were not related to disease duration. In the cerebral cortex, the diffuse plaques were more commonly evenly distributed or occurred in large clusters along the cortex parallel to the pia mater compared with the florid plaques which occurred more frequently in regularly distributed clusters. CONCLUSION: The florid plaques may not be derived from the diffuse plaques, the 2 plaque types appearing to develop independently with unique factors involved in their pathogenesis.

Adolescent↗

PubMed1983

The physiological basis of mental images.

An important hypothesis in neurophysiology supposes that sensory information is encoded in spatial patterns of neural activity. A test of this hypothesis in rabbits reveals that the spatial pattern of encephalographic (EEG) activity of the olfactory bulb depends less on odor than on expectation of odor. Analysis of the structure and nonlinear dynamics of the olfactory system suggests that the EEG manifests a neural activity pattern that is an active filter corresponding to what ethologists call a "chemical search image." This first glimpse at the physical aspect of what may be a primitive form of mental image allows us to infer some of its properties. It is self-organized; input destabilizes the bulb, and the event runs a course that is shaped by the initial conditions, the sensory input, the chemical state of the bulb from centrifugal input, and the record of past input embedded in synaptic connections. The event is analog, but not an analog of input. Its intensity pattern exists in two dimensions but it is not a picture. Its bases in feedback and resonance make it connotative and ascriptive, not denotative or descriptive. The neural-mental image is an operator, not an operand. It gathers neurons by the millions into coherent activity and creates information, which it transmits to the next stage in the brain, thereby helping to shape behavior. It cannot be understood without reference to both what the subject does and what is done to it. Its function in the bulb is to regulate olfactory input with minimal and nonspecific centrifugal control.

Animals↗

PubMed1993

The human sucrase-isomaltase gene directs complex patterns of gene expression in transgenic mice.

Sucrase-isomaltase (SI) is an enterocyte-specific gene that is expressed in complex developmental and spatial patterns. In this study, we examine the ability of regulatory elements within the human SI (hSI) gene to direct appropriate cell lineage and spatial patterns of expression in transgenic mice. Transgenic mouse lines were established using a construct containing bases -3424 to +54 of the hSI gene linked to the human growth hormone (hGH) structural gene. In each transgenic line, hGH mRNA and protein were expressed only in the small intestine and colon. In contrast to the endogenous mouse SI (mSI) gene, which was expressed along the entire length of the small intestine, hGH mRNA expression was predominantly found in the distal jejunum and ileum, with very low levels in more proximal portions of the small intestine. However, the pattern of transgene expression along the small intestinal crypt-villus axis was identical to the pattern of the endogenous mSI gene. These results suggest that regulatory elements necessary for intestine-specific transcription and differential expression along the intestinal crypt-villus axis are included in the 5'-flanking region of the hSI gene. Furthermore, these data suggest that different DNA regulatory regions regulate transcription along the horizontal intestinal axis. In the colon, there was aberrant expression of hGH in a subpopulation of enteroendocrine cells that contained peptide tyrosine tyrosine (PYY). This suggests that there are DNA regulatory elements, missing in the transgene construct, which normally suppress expression of the endogenous mSI gene in these cells. Taken together, these findings define the SI gene as a useful model for studies of differentiation, cell lineage determination, and mechanisms of complex spatial gene expression in the intestine.

Animals↗

PubMed2006

Inferring colonization history from analyses of spatial genetic structure within populations of Pinus strobus and Quercus rubra.

Many factors interact to determine genetic structure within populations including adult density, the mating system, colonization history, natural selection, and the mechanism and spatial patterns of gene dispersal. We examined spatial genetic structure within colonizing populations of Quercus rubra seedlings and Pinus strobus juveniles and adults in an aspen-white pine forest in northern Michigan, USA. A 20-year spatially explicit demographic study of the forest enables us to interpret the results in light of recent colonization of the site for both species. We assayed 217 Q. rubra seedlings and 171 P. strobus individuals at 11 polymorphic loci using nine allozyme systems. Plant genotypes and locations were used in an analysis of spatial genetic structure. Q. rubra and P. strobus showed similar observed levels of heterozygosity, but Q. rubra seedlings have less heterozygosity than expected. Q. rubra seedlings show spatial genetic clumping of individuals on a scale to 25 m and levels of genetic relatedness expected from the clumped dispersion of half-siblings. In contrast, P. strobus has low levels of genetic relatedness at the smallest distance class and positive spatial genetic structure at scales < 10 m within the plot. The low density of adult Q. rubra outside the study plot and limited, spatially clumped rodent dispersal of acorns is likely responsible for the observed pattern of spatial genetic structure and the observed heterozygote deficit (i.e. a Wahlund effect). We attribute weaker patterns observed in P. strobus to the longer dispersal distance of seeds and the historical overlap of seed shadows from adults outside of the plot coupled with the overlap of seed shadows from younger, more recently established reproductive adults. The study demonstrates the utility of long-term demographic data in interpreting mechanisms responsible for generating contemporary patterns of genetic structure within populations.

Genetic Variation↗

PubMed2000

Learning of spatial and temporal patterns in sequential hand movements.

Speed and accuracy in performing a complex movement sequence improve with practice. To examine how the temporal and spatial patterns of movement sequence are learned, the sequence of target locations and the consistency in the timing of target presentation were manipulated independently while subjects produced a series of visually guided hand movements. When the sequence of target locations and the timing of target presentation followed a consistent pattern, performance for a particular movement sequence improved with practice for both temporal and spatial movement parameters. However, when the same temporal and spatial patterns were recombined with a phase shift, there was a small but consistent deficit in performance. These results suggest that whereas spatial and temporal patterns in a learned movement sequence can be recombined flexibly, optimal performance is obtained for a specific spatio-temporal pattern of movement sequence. Whereas subjects were largely aware of the spatial and temporal patterns, they were unaware of the phase-shift, suggesting that learning of a specific spatio-temporal pattern was implicit.

Hand↗

PubMed1997

Spatial statistical analysis of Chinese cancer mortality: a comparison study of the D statistic.

In this paper, we study a nonparametric spatial pattern test statistic, the D statistic. The D statistic is an effective test statistic for testing spatial patterns in regional health data. Comparison studies of the D statistic with fixed weights and random weights are illustrated on the atlas of the Chinese cancer mortality rates and on other cancer atlas. Some social, economic and environmental reasons for statistically significant spatial autocorrelations of the Chinese cancer mortality rates were given in the discussion section. The method for calculating the mean and the variance of the randomly weighted D statistic is given in the appendix.

China↗

PubMed2006

Fine spatiotemporal structure of phase in human intracranial EEG.

OBJECTIVE: To transfer to the clinic for humans the technology and theory for high-resolution EEG analysis that have been developed in the laboratory with animals. METHODS: EEGs were recorded at high spatial resolution from a 1 x 1 cm 8 x 8 electrode array on the right inferior temporal gyrus of a patient undergoing preoperative monitoring for epilepsy surgery. Cosines were fitted to EEG segments to measure frequency and phase and compute location, size, latency, phase velocity, duration, and recurrence rate of radially symmetric spatial patterns called phase cones. The Hilbert transform was also used to get high temporal resolution. RESULTS: In the awake state, the power spectral density (PSD) showed power-law decrease in log power with log frequency at 1/falpha, alpha approximately 2, but with peaks in the standard empirical ranges. The phase in beta and gamma ranges had spatial gradients in conic form. Resetting of these stable spatial patterns of phase cones was spatially coincident at intermittent discontinuities ('phase slip') recurring at theta rates. Cones had half power diameters from 2 to 50+ mm; their durations had power-law distributions with values ranging from 6 to 300+ ms depending on length of the analysis window. In slow wave sleep PSD decreased at 1/falpha, alpha approximately 3,with loss of beta-gamma spectral peaks and diminished or absent oscillations and spatiotemporal phase structure. CONCLUSIONS: Spatiotemporal structures in awake human and rabbit EEG showed striking similarities. The only clear differences were ascribable to differing scales of measurement. These fine spatiotemporal structures of EEG were diminished or lost in slow wave sleep. SIGNIFICANCE: The fine structure indicates that neocortical stability is sustained at self-organized criticality; that synaptic input in the awake state drives neocortex away from criticality causing beta-gamma oscillations in re-stabilizing 'neural avalanches'; and that diminished input in slow wave sleep allows return toward criticality but with some added risk of instability and seizure.

Adult↗

PubMed2002

A geostatistical analysis of the geographic distribution of lymphatic filariasis prevalence in southern India.

Gaining a better understanding of the spatial population structure of infectious agents is increasingly recognized as being key to their more effective mapping and to improving knowledge of their overall population dynamics and control. Here, we investigate the spatial structure of bancroftian filariasis distribution using geostatistical methods in an endemic region in Southern India. Analysis of a parasite antigenemia prevalence dataset assembled by sampling 79 villages selected using a World Health Organization (WHO) proposed 25 x 25 km grid sampling procedure in a 225 x 225 km area within this region was compared with that of a corresponding microfilaraemia prevalence dataset assembled by sampling 119 randomly selected villages from a smaller subregion located within the main study area. A major finding from the analysis was that once large-scale spatial trends were removed, the antigenemia data did not show evidence for the existence of any small-scale dependency at the study sampling interval of 25 km. By contrast, analysis of the randomly sampled microfilaraemia data indicated strong spatial contagion in prevalence up to a distance of approximately 6.6 kms, suggesting the likely existence of small spatial patches or foci of transmission in the study area occurring below the sampling scale used for sampling the antigenemia data. While this could indicate differences in parasite spatial population dynamics based on antigenemia versus microfilaraemia data, the result may also suggest that the WHO recommended 25 x 25 km sampling grid for rapid filariasis mapping could have been too coarse a scale to capture and describe the likely local variation in filariasis infection in this endemic location and highlights the need for caution when applying uniform sampling schemes in diverse endemic regions for investigating the spatial pattern of this parasitic infection. The present results, on the other hand, imply that both small-scale spatial processes and large-scale factors may characterize the observed distribution of filariasis in the study region. Our preliminary analysis of a mountain range associated large-scale trend in the antigenemia data suggested that a nonlinear relationship of infection prevalence with elevation might be a factor behind such observed global spatial patterns. We conclude that geostatistic methods can provide a powerful framework for carrying out the empirical investigation and analysis of parasite spatial population structure. This study shows that their successful application, however, will crucially depend on our gaining a more thorough understanding of the appropriate geographic scales at which spatial studies should be carried out.

Adult↗

PubMed2001

Viewing odors in the mushroom body of the fly.

Central processing of olfactory information has been analyzed in the mushroom body of Drosophila by Ca(2+) imaging, extending such analysis of odor coding to the second relay of the olfactory system. Different odors, and different concentrations of a particular odor, yield distinct spatial patterns of activity. Mutations that affect odor receptors and odorant-binding proteins affect these spatial patterns.

Animals↗

PubMed2003

Historical and current atmospheric deposition to the epilithic lichen Xanthoparmelia in Maricopa County, Arizona.

Spatial patterns of atmospheric deposition of trace elements to an epilithic lichen were assessed using a spatial grid of 28 field sites in 1998 throughout Maricopa County, Arizona, USA. In addition, samples of Xanthoparmelia spp. from Arizona State University lichen herbarium material (1975-1976) was utilized for a limited number of sites in order to explore temporal trends. The lichen material was cleaned, wet digested and analyzed by ICP-MS for a suite of elemental concentrations [antimony (Sb), cadmium (Cd), cerium (Ce), chromium (Cr), cobalt (Co), copper (Cu), dysprosium (Dy), europium (Eu), gadolinium (Gd), gold (Au), holmium (Ho), lead (Pb), lutetium (Lu), neodymium (Nd), nickel (Ni), palladium (Pd), platinum (Pt), praseodymium (Pr), samarium (Sm), scandium (Sc), silver (Ag), terbium (Tb), thulium (Tm), tin (Sn), uranium (U), ytterbium (Yb), yttrium (Y), and zinc (Zn)]. Cluster analysis and principal component analysis suggest three major factors, which, depending on regional aerosol fractionation, explain most of the variation in elemental signatures: (1) a group of widely distributed rare earth elements (2) a highly homogenous Co, Cr, Ni, and Sc component representing the influence of mafic rocks, and (3) anthropogenic emissions. Elemental concentrations in Maricopa County lichens were generally comparable to those reported for relatively unpolluted areas. Only highly urbanized regions, such as the greater Phoenix Metropolitan Area and the NW corner of the county, exhibited elevated concentrations for Zn, Cu, Pb, and Cd. Lead levels in lichens have fallen over the last 30 years by 71%, while Zn concentrations for some regions have increased by as much as 245%. From the spatial pattern of elemental deposition for Cd, Cu, Ni, Pr, Pb, and Cu, we infer that agriculture, mining, industrial activities, and traffic probably are the major air pollutant sources in Maricopa County.

Air Pollutants↗

PubMed1998

Fertile offspring derived from mammalian eggs lacking either animal or vegetal poles.

In all animals so far tested, removing either pole of the undivided egg prevents normal development: embryos may arrest early, lack organs, or the adults may be sterile. These experiments have shown that spatial patterning of the egg is of utmost importance for subsequent development. However, the significance of spatial patterning in mammalian eggs is still controversial. To test the importance of egg polarity in the mouse a substantial amount of material either from the animal (polar body-associated) or the vegetal (opposite) pole of the fertilised egg was removed. One pole of the egg was cut away manually with a glass needle and the eggs were allowed to develop in vitro. Both kinds of surgical operation permit the development of blastocysts, which, after transfer to the uteri of pseudo-pregnant foster mothers, can produce viable offspring. Furthermore, these develop into fertile adult mice. I conclude that mouse eggs have no essential components that are localised uniquely to the animal or the vegetal pole and, therefore, do not rely for their axial development on maternal determinants that are so localised in the fertilised egg. Thus the mammalian egg appears to be very unusual in the animal kingdom in that it establishes the embryonic axes after the zygote has begun development.

Animals↗

PubMed1982

Motion and vision. IV. Isotropic and anisotropic spatial responses.

When the thresholds for periodic spatial patterns containing two or more differently oriented components (e.g., crossed gratings) are measured under normal, unstabilized conditions, each component seems to be detected almost independently of the others if their angular orientations are sufficiently different. This psychophysical behavior has been attributed to anisotropic or orientation-tuned units in the visual cortex. Here we report that when the image of such a multicomponent pattern is stabilized on the retina, the independent-detection behavior vanishes. Under stabilized-image conditions, the contrast sensitivity is governed by the maximum local contrast at the retina. The number and relative contrast of individual components, even orthogonal ones, behave almost additively in making up the threshold contrast. We confirmed this conclusion with a variety of patterns that give orientation-tuning effects in unstabilized viewing. Controlled image motion (resembling the effect of the natural drifts of the eye) restores the independent-detection behavior in every case, as do other forms of temporal modulation (e.g., flicker or flash presentations). We infer (1) that orientation-tuned units in man do not respond to unchanging stimuli--they cannot function unless the pattern on the retina is temporally modulated, and (2) in the absence of temporal modulation, spatial patterns are detected by isotropic units of relatively low sensitivity.

Biomedical Engineering↗

PubMed2000

Temporal properties of high frequency intra-QRS signals in myocardial infarction and healthy hearts.

The prevalence of late potentials after myocardial infarction depends on the site of the infarction. This may be caused by the different activation onsets of the anterior and inferior myocardial segments. Therefore, in anterior infarcts the high frequency signals may be concealed within the QRS whereas in the inferior infarcts they last beyond the end of the QRS. We compared the timing and the spatial patterns of high frequency intra-QRS signals (IQSs) in the different infarction sites. We investigated 14 patients with anterior infarcts, 17 patients with inferior infarcts, and 10 healthy subjects. 31-lead magnetocardiograms were recorded in left precordial position and averaged. The QRS signals were smoothed with a Savitzky-Golay filter. The smoothed QRS signals were subtracted from the measured ones. The difference of the signals (frequency band of about 60-200 Hz) representing the high frequency components was quantified. The percentage of the high frequency signals was calculated for the entire QRS, for the first and for the second half, respectively. We found that in patients with anterior infarcts the high frequency components predominantly appeared in the first half of the QRS whereas in inferior infarcts these components predominantly appeared in the second half of the QRS. The different infarction sites were associated with different spatial patterns of the high frequency signals on the body surface. In healthy subjects there was not such a preferential association of time intervals and high frequency signals. Late potentials are the special case of high frequency signals appearing in the terminal QRS. It is the general property of the myocardium to generate high frequency signals associated with the depolarization of infarcted tissue. The timing of such signals and the spatial distribution patterns on the body surface may help to identify the location of the sources.

Aged↗

PubMed2002

Differential patterns of spatial divergence in microsatellite and allozyme alleles: further evidence for locus-specific selection in the acorn barnacle, Semibalanus balanoides?

We compared patterns of genetic structure at potentially selected (two allozyme loci) and neutral molecular markers (six microsatellite loci) in the acorn barnacle, Semibalanus balanoides from the Gulf of St. Lawrence. Our results confirmed the presence of a geographical shift in alleles MPI and GPI near the Miramichi River. In contrast, no significant patterns of population differentiation among samples located north and south of the river mouth were detected for four of six microsatellite loci. However, analysis of molecular variance (amova) at individual loci revealed that a significant proportion of the total variance in allele frequencies was partitioned among samples located north and south of the river for both the allozyme and the other two microsatellite loci. The two most common alleles at these microsatellites showed frequencies that were highly correlated (r = 0.65-0.74, P < 0.05) with those of the MPI*2 allele, perhaps because of either physical linkage or epistasis. The two allozyme loci were significantly correlated in barnacles located north of the Miramichi River (r = 0.86, P < 0.05). Overall, our results supported the hypothesis that the broad scale pattern of allozyme allelic shifts is maintained by selection. They also indicated that microsatellites may not always behave in a neutral way and must be used cautiously, especially when evidence for genetic structuring relies on only a few assayed loci.

Alleles↗

PubMed2004

[Statistical methods to analyze risk with spatial distribution patterns].

The development of the geographic information systems has improved the interest in analyzing the characteristics of the population, taking into account the place where they live. The health of the population, measured as the risk of morbidity or mortality, is conditioned by the variety of risk factors characteristic of the region which cannot be measured. Analysis of spatial models considers the dependence of the health indicators between close regions. This dependence is due to the existence of the risk factors that are not measured but are shared by the region. Thus, the spatial distribution of these indicators depends on the geographic pattern of these risk factors. In this study, some limitations of the standardized methods and the Poisson regression used to model the spatiality are discussed and the advantages of the spatial models are shown. The methodology is illustrated by the insulin-dependent diabetes type 1 data from Catalonia during 1989 and 1998.

Demography↗