SEARCH · PubMed Health

Results for “spatial dependency”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources

PubMed2005

[Spatial heterogeneity of soil moisture after raining at forest-grassland landscape boundary in hilly area of Loess Plateau].

Soil moisture is a main factor limiting vegetation restoration in semi-arid region. In this paper, the spatial variability of different layers soil moisture after raining at the forest-grassland boundary in hilly area of Loess Plateau were studied by traditional and geostatistical analysis methods. The results showed that the moisture content in surface (0 - 10 cm) and subsurface soil layer (10 - 20 cm) of grassland was higher than that of forestland. The two layers soil moisture content at forest-grassland boundary showed a small variation but an obvious ecological distribution. By using moving split-window techniques, it was obtained that the width of edge influence in surface and subsurface layer was 8 and 6 m, respectively. Geostatistical analyses showed that the spatial distribution of two layers soil moisture had a pure nugget effect in grassland, linear model in forestland, and spherical model in forest-grassland boundary. The spatial heterogeneity of two layers soil moisture was higher at forest-grassland boundary than at forestland and grassland, which had a stronger spatial dependence and autorelation. Kriging maps expressed the spatial structural characters. The distribution of soil moisture in two layers showed a strip shape near forest edge, and a patch shape far from the edge.

China↗

PubMed2006

Spatial learning and goldfish telencephalon NMDA receptors.

Recent results have demonstrated that the mammalian hippocampus and the dorso-lateral telencephalon of ray-finned fishes share functional similarities in relation to spatial memory systems. In the present study, we investigated whether the physiological mechanisms of this hippocampus-dependent spatial memory system were also similar in mammals and ray-finned fishes, and therefore possibly conserved through evolution in vertebrates. In Experiment 1, we studied the effects of the intracranial administration of the noncompetitive NMDA receptor antagonist MK-801 during the acquisition of a spatial task. The results indicated dose-dependent drug-induced impairment of spatial memory. Experiment 2 evaluated if the MK-801 produced disruption of retrieval of a learned spatial response. Data showed that the administration of MK-801 did not impair the retrieval of the information previously stored. The last experiment analyzed the involvement of the telencephalic NMDA receptors in a spatial and in a cue task. Results showed a clear impairment in spatial learning but not in cue learning when NMDA receptors were blocked. As a whole, these results indicate that physiological mechanisms of this hippocampus-dependent system could be a general feature in vertebrate, and therefore phylogenetically conserved.

Animals↗

PubMed1997

Spatial learning and memory at defined points of the estrous cycle: effects on performance of a hippocampal-dependent task.

Learning based on hippocampal-dependent spatial navigation in female rats was assessed at identified points in the estrous cycle corresponding to low (estrus) and high (proestrus) circulating estrogen. With background training in water-maze procedures, rats learned the location of an escape platform in the maze in a single session of 8 training trials. A strong spatial bias for the escape platform was also evident in a probe trial used to assess retention of learning 30 min after the training session. This entire protocol was completed in less than an hour. The performance of the estrus and proestrus rats was indistinguishable on all behavioral measures, irrespective of the stage of estrous cycle during the task. These results indicate that rapid learning and retention for spatial information over a relatively short interval may be preserved despite morphological alterations in hippocampal dendritic spine density in the normally cycling female rat.

Animals↗

PubMed2026

A divide and conquer strategy for recapitulating whole genome 3D structure using Hi-C data.

The three dimensional (3D) spatial organization of the genome is closely linked to biological functions and can be captured by Hi-C assays through interrogating genome-wide chromatin interactions. Methodologies for inferring 3D structures from Hi-C data summarized as a two-dimensional (2D) contact matrix can be broadly placed within the paradigms of optimization-based and sampling-based. Many optimization-based methods are capable of constructing whole genome 3D structures but do not account for spatial dependency in the 2D data matrix nor cell heterogeneity in bulk Hi-C data, which provide an average over millions of cells. Sampling-based methods, on the other hand, are probabilistic model-based and can account for not only dependency, heterogeneity, but also other features inherent in Hi-C data, such as over-dispersion and sparsity. However, whole-genome 3D structure recapitulation is too computationally expensive for sampling-based methods, while chromosome-by-chromosome strategies for sampling-based methods ignore important information on inter-chromosomal contacts. To address these issues, we propose the truncated Random effect EXpression-cut and paste (tREX-cap) method, which applies the tREX model within a divide and conquer strategy. The resulting method inherits the good data-feature-cognizant properties of tREX and, in the meantime, can efficiently infer the whole genome 3D structure. We demonstrate the performance of tREX-cap through an extensive simulation study and analyses of a Hi-C lymphoblastoid dataset and a Hi-C IMR90 dataset.

Humans↗

PubMed2005

Differential induction of c-Jun and Fos-like proteins in rat hippocampus and dorsal striatum after training in two water maze tasks.

Research examining the neuroanatomical bases of memory in mammals suggests that the hippocampus and dorsal striatum are parts of independent memory systems that mediate "cognitive" and stimulus-response "habit" memory, respectively. At the molecular level, increasing evidence indicates a role for immediate early gene (IEG) expression in memory formation. The present experiment examined whether acquisition of cognitive and habit memory result in differential patterns of IEG protein product expression in these two brain structures. Adult male Long-Evans rats were trained in either a hippocampal-dependent spatial water maze task, or a dorsal striatal-dependent cued water maze task. Ninety minutes after task acquisition, brains were removed and processed for immunocytochemical procedures, and the number of cells expressing Fos-like immunoreactivity (Fos-like-IR) and c-Jun-IR in sections from the dorsal hippocampus and the dorsal striatum were counted. In the dorsal hippocampus of rats trained in the spatial task, there were significantly more c-Jun-IR pyramidal cells in the CA1 and CA3 regions, relative to rats that had acquired the cued task, yoked controls (free-swim), or naïve (home cage) rats. Relative to rats receiving cued task training and control conditions, increases in Fos-like IR were also observed in the CA1 region of rats trained in the spatial task. In rats that had acquired the cued task, patches of c-Jun-IR were observed in the posteroventral striatum; no such patches were evident in rats trained in the spatial task, yoked-control rats, or naïve rats. The results demonstrate that IEG protein product expression is up-regulated in a task-dependent and brain structure-specific manner shortly after acquisition of cognitive and habit memory tasks.

Animals↗

PubMed2006

Disease mapping and spatial regression with count data.

In this paper, we provide critical reviews of methods suggested for the analysis of aggregate count data in the context of disease mapping and spatial regression. We introduce a new method for picking prior distributions, and propose a number of refinements of previously used models. We also consider ecological bias, mutual standardization, and choice of both spatial model and prior specification. We analyze male lip cancer incidence data collected in Scotland over the period 1975-1980, and outline a number of problems with previous analyses of these data. In disease mapping studies, hierarchical models can provide robust estimation of area-level risk parameters, though care is required in the choice of covariate model, and it is important to assess the sensitivity of estimates to the spatial model chosen, and to the prior specifications on the variance parameters. Spatial ecological regression is a far more hazardous enterprise for two reasons. First, there is always the possibility of ecological bias, and this can only be alleviated by the inclusion of individual-level data. For the Scottish data, we show that the previously used mean model has limited interpretation from an individual perspective. Second, when residual spatial dependence is modeled, and if the exposure has spatial structure, then estimates of exposure association parameters will change when compared with those obtained from the independence across space model, and the data alone cannot choose the form and extent of spatial correlation that is appropriate.

Epidemiologic Methods↗

PubMed1984

Fundamentals of NMR imaging.

NMR imaging is a new kind of emission tomography that utilizes the resonance frequency radiation emitted by atomic nuclei, in particular the hydrogen nuclei, present in the human body. This radiation is emitted when these nuclei are in a state of vibration under the influence of a static magnetic field and after excitation by an external RF radiation pulse. By introducing well-known field inhomogeneities the frequency of the emitted radiation can be made spatially dependent. Through spectroscopic analyses and mathematical procedures the spatial distribution of the emission intensity, the NMR image, can be reconstructed. Characteristic differences in concentration and resonance properties of the hydrogen nuclei result in strong contrasts in the image between the various tissues, as well as between lesions and normal tissue. Due to a choice of imaging techniques and time parameter settings the NMR image contrasts can be varied widely. Shifting or rotation of the image plane is performed electronically without changing the patient's position. Multiple parallel slices as well as a 3-dimensional volume can be imaged in one measuring procedure.

Adipose Tissue↗

PubMed2005

Patterns of expression of Bax, Bcl-2 and Bcl-x(L) in the implantation site in rat during pregnancy.

The uterine endometrium responds to blastocyst implantation with extensive proliferation and differentiation of stromal cells into decidual cells, forming the antimesometrial and mesometrial decidua. These undergo regression by apoptosis but as this process occurs at different time periods suggest that there is spatially dependent temporal control of apoptosis in these specific regions. To elucidate the role of the mitochondrion-dependent signalling pathway in tissue regression, we investigated the spatial and temporal pattern of expression of the Bcl-2 family members in uterine tissues of the implantation site, from the post-implantation period to parturition. Furthermore, the activities of the initiator caspases-8 and -9, and of the executioner caspase-3 were determined. Overall Bax and Bcl-2 were expressed from day 8 till day 19, whilst Bcl-x(L) was extinguished by day 16. In the antimesometrial and in the mesometrial decidua both Bcl-2 and Bax declined from days 10 to 12. In the latter Bcl-2 immunoreactivity decreased till the end of pregnancy, whilst for Bax a constant level remained thereafter. The pattern of variation of enzymatic activities throughout pregnancy for all the enzymes was similar, increasing from days 10 to 14 and decreasing towards the end of pregnancy. The increased levels of active caspase-9 correlated with Bax/Bcl-2 and Bcl-x(L) expression suggesting that the apoptotic mitochondrion-dependent pathway is involved in decidual regression during pregnancy progression.

Animals↗

PubMedDate not supplied

Firing characteristics of deep layer neurons in prefrontal cortex in rats performing spatial working memory tasks.

Single cells were recorded with 'tetrodes' in regions of the rat medial prefrontal cortex, including those which are targets of hippocampal afferents, while rats were performing three different behavioral tasks: (i) an eight-arm radial maze, spatial working memory task, (ii) a figure-eight track, delayed spatial alternation task, and (iii) a random food search task in a square chamber. Among 187 recorded units, very few exhibited any evidence of place-specific firing on any of the behavioral tasks, except to the extent that different spatial locations were related to distinct phases of the task. Furthermore, no prefrontal unit showed unambiguous spatially dependent delay activity that might mediate working memory for spatial locations. Rather, the cells exhibited diverse correlates that were generally associated with the behavioral requirements of performing the task. This included firing related to intertrial intervals, onset or end of trials, selection of specific arms on the eight-arm radial maze, delay periods, approach to or departure from goals, and selection of paths on the figure-eight track. Although a small number of cells showed similar behavioral correlates across tasks, the majority of cells showed no consistent correlate when recorded across multiple tasks. Furthermore, some units did not exhibit altered firing patterns in any of the three tasks, while others showed changes in firing that were not consistently related to specific behaviors or task components. These results are in agreement with previous lesion and behavioral studies in rats that suggest a prefrontal cortical role in encoding 'rules' (i.e. structural features) or behavioral sequences within a task but not in encoding allocentric spatial information. Given that the hippocampal projection to this cortical region is capable of undergoing LTP, our data lead to the hypothesis that the role of this projection is not to impose spatial representations upon prefrontal activity, but to provide a mechanism for learning the spatial context in which particular behaviors are appropriate.

Action Potentials↗

PubMed1984

Pentoxifylline reverses age-related deficits in spatial memory.

Pentoxifylline, a phosphodiesterase inhibitor, produces a marked reversal of an age-dependent spatial memory deficit in Fischer 344 strain male rats. Performance of 26-month-old animals treated chronically with pentoxifylline approached that of 3-month-old controls. The effect was not dependent upon concurrent administration of the acetylcholine precursor choline chloride. It is concluded that the pentoxifylline-induced reversal of the age-dependent memory decline is not dependent on any presumed facilitation of acetylation and utilization of exogenously supplied transmitter substrate.

Aging↗

PubMed2001

High levels of estradiol disrupt conditioned place preference learning, stimulus response learning and reference memory but have limited effects on working memory.

The present study investigated the effects of high levels of estradiol in female rats on four different radial arm maze tasks: the hippocampus-dependent spatial working-reference memory task; the prefrontal cortex-hippocampus dependent delayed win-shift task; the striatum-dependent cued win-stay task; and the amygdala-dependent conditioned place preference task. Ovariectomized female rats were injected daily with either 10 microg of estradiol benzoate or sesame oil vehicle approximately 4 h prior to testing. In Experiment 1, treatment with estradiol disrupted learning on the spatial working-reference memory task by increasing the number of reference memory errors to reach criterion. In Experiment 2, treatment with estradiol had no significant effect on the delayed win-shift task. In Experiment 3, treatment with estradiol resulted in impaired performance on a striatum-dependent cued win-stay task. In Experiment 4, treatment with estradiol impaired the acquisition of a conditioned place-preference task. Taken together these findings suggest that high levels of estradiol inhibit reference memory, stimulus response learning, and amygdala-dependent appetitive conditioning while having little effect on working memory.

Amygdala↗

PubMed2006

Three-dimensional vibrational imaging of a microcrystalline J-aggregate using supercontinuum-based ultra-broadband multiplex coherent anti-stokes Raman scattering microscopy.

Vibrational properties of a porphyrin J-aggregate microcrystal have been investigated by ultra-broadband multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy using a supercontinuum light source generated from a photonic crystal fiber. Owing to a strong resonance effect due to an excitonic transition, clear spectral and spatial profiles of the CARS signal have been successfully obtained. On the basis of the comparison between the CARS and the fluorescence images, the spatial dependence of the CARS signal can be explained by the spatial inhomogeneity of the excitonic transition energy in the single J-aggregate microcrystal.

Journal Article↗

PubMed1999

The spatial distribution of larvae of Culicoides impunctatus biting midges.

The spatial distribution of Culicoides impunctatus Goetghebuer (Diptera: Ceratopogonidae) larvae was sampled at a site in western Scotland, and geostatistical analyses were used to quantify spatial dependencies. Nested sampling and analysis indicated that most of the spatial variance occurred within distances of 160-640 cm, levelling off at distances >640 cm. Semivariograms for transformed data from three 100 m x 100 m grids showed similar, isotropic patterns for larval counts, soil organic content, soil water content and the distribution of Juncus spp. rushes, with the variance increasing with separation distance. High levels of significance were associated with power models used to describe the semivariograms, which was indicative of the absence of a plateau (or 'sill') in the respective data. Correlation analysis of transformed data revealed significantly positive relationships between larval counts and soil pH, soil percentage organic content, soil percentage water content and also the distribution of Sphagnum spp., Juncus spp. and Myrica gale. There were also significantly negative relationships between larval counts and the distribution of Pteridium aquilinum and all mosses other than Sphagnum spp. The results suggest a far more structured and predictable pattern of C. impunctatus larval sites than previous studies and are discussed in relation to their application in localized Culicoides control and to studies of the mechanisms determining the spatial distribution of C. impunctatus larvae.

Animals↗

PubMedDate not supplied

[Spatial analysis of early neonatal mortality in the municipality of Rio de Janeiro, 1995-1996].

The objective of this study was to establish the spatial distribution of the early neonatal mortality rate (0-3 days) in the municipality of Rio de Janeiro for 1995-1996, identifying the best explanatory factors for spatial variations. By considering Rio de Janeiro's 153 neighborhoods as ecological units of analysis, socioeconomic and maternal indicators were analyzed according to place of residence. Spatial statistical analysis was performed using the Cliff & Ord methodology, appropriate for lattice data. From the 0-3 day mortality thematic map, we clearly identified two clusters of high early neonatal mortality rates. Spatial dependence was also confirmed by the statistical results of the spatial analysis. The variables that explain the clusters are the proportions of "adolescent mothers", "slum-dwellers", and "heads of households below the poverty level". Spatial statistics provided a better understanding of the geographic distribution of early neonatal mortality and suggested potential hypotheses for further investigation, which could support preventive programs and contribute to a decrease in infant mortality.

Adolescent↗

PubMed1990

Spatial misregistration of vascular flow during MR imaging of the CNS: cause and clinical significance.

Spatial misregistration of signal recovered from flowing spins within vascular structures is a common phenomenon seen in MR imaging of the CNS. The condition is displayed as a bright line or dot offset from the true anatomic location of the lumen of the imaged vessel. Its origin is the time delay between application of the phase- and frequency-encoding gradients used to locate spins within the plane of section. The principal condition necessary for the production of spatial misregistration is flow oblique to the axis of the phase-encoding gradient. Flow-related enhancement (entry slice phenomenon), even-echo rephasing, and gradient-moment nulling contribute to the production of the bright signal of spatial misregistration. Familiarity with the typical appearance of flow-dependent spatial misregistration permits confirmation of a vessel's patency; identification of the direction of flow; estimation of the velocity of flow; and differentiation of this flow artifact from atheromas, dissection, intraluminal clot, and artifacts such as chemical shift.

Blood Flow Velocity↗

PubMedDate not supplied

Spatial misregistration of vascular flow during MR imaging of the CNS: cause and clinical significance.

Brain↗

PubMed2006

Hippocampal synaptic plasticity and water maze learning in cocaine self-administered rats.

Previously, we have shown that long-term potentiation (LTP) in hippocampus of Lewis rats was significantly modulated by cocaine self-administration. Using a single train of high-frequency stimulation of 100 Hz for 1s (HFS), we found an enhancement of LTP after cocaine self-administration that was maintained even during the extinction of this behavior. However, the effects of cocaine self-administration on a hippocampal-dependent spatial learning task were unknown. Therefore, in the present study our first objective was to analyze if cocaine self-administration might affect the performance in a hippocampus-dependent task, such as the Morris water maze test. Male adult Lewis (LEW) rats self-administered cocaine (1 mg/kg/injection) or saline (0.9% NaCl) for 3 weeks. Three hours after finishing the last self-administration session, animals were submitted to Morris water maze training for 3 consecutives days. A memory test was carried out 24 h after the last training session. No significant differences were found in escape latencies and time spent in the quadrant where the platform was located during training. Given that we did not find any cocaine effect on this spatial learning task, our second objective was to estimate indirectly if brain cocaine levels have failed to modulate LTP in animals that were performing the water maze trials. To this end, we tested if cocaine application to hippocampal slices of naïve subjects was able to evoke LTP. The results indicated that cocaine produced an enhanced LTP in these hippocampal slices. Taking together, the results of the present study suggest that hippocampal LTP-like processes generated after cocaine self-administration are not related to spatial learning hippocampal-dependent tasks, such as the water maze test.

Animals↗

PubMed2002

Contrast-dependent changes in spatial frequency tuning of macaque V1 neurons: effects of a changing receptive field size.

Previous studies on single neurons in primary visual cortex have reported that selectivity for orientation and spatial frequency tuning do not change with stimulus contrast. The prevailing hypothesis is that contrast scales the response magnitude but does not differentially affect particular stimuli. Models where responses are normalized over contrast to maintain constant tuning for parameters such as orientation and spatial frequency have been proposed to explain these results. However, our results indicate that a fundamental property of receptive field organization, spatial summation, is not contrast invariant. We examined the spatial frequency tuning of cells that show contrast-dependent changes in spatial summation and have found that spatial frequency selectivity also depends on stimulus contrast. These results indicate that contrast changes in the spatial frequency tuning curves result from spatial reorganization of the receptive field.

Animals↗