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Results for “spatial dependency”

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At least 289 records · Page 16Linked to original sources

PubMed2000

Grape cane gallmaker (Coleoptera: Curculionidae) and its impact on cultivated grapes.

The grape cane gallmaker, Ampeloglypter sesostris (Leconte), is a native weevil that infests new shoots of wild and cultivated grapes (Vitis spp.). Females oviposit on the tender portions of new shoots, producing a reddish gall that can expand the shoot to twice its normal diameter. These galls can be quite numerous in eastern vineyards, and their effects are unknown. We studied the spatial distribution of grape cane gallmaker and its impact on berry size, sugar content, and nutrient and mineral uptake. We observed spatial trends in grape cane gallmaker distribution in vineyards adjacent to woodland margins, with the trend emanating from the woodline. In vineyards without woodland margins, there was little spatial dependency in grape cane gallmaker distribution in individual years. However, grape cane gallmaker density on a single vine was spatially cross-correlated between 2 yr. The presence of galls did not significantly affect berry quality, or the uptake of nutrients and minerals, and we conclude that grape cane gallmaker does not negatively impact berry quality or mature vine vigor.

Animals↗

PubMed1994

Histamine effect on human cutaneous blood flow: regional variations.

Different reactivities of small blood vessels to the histamine released by exogenous and endogenous substances may play a role in the regional variations of the elicited cutaneous response. To study the regional dependence of cutaneous blood flow in response to histamine, the compound was administered intradermally (prick introduction), thereby bypassing the spatially dependent penetration process. The induced response was quantified with cutaneous blood flow measurements utilizing laser Doppler flowmetry. Extent of response and time parameters were compared. Three anatomical sites, the back, volar side of the forearm, and ankle, were studied on 20 volunteers (10 men and 10 women, age 24-34). For comparison, topical administration was also performed. Significant differences in the measured responses at the three sites were observed: the increase of the cutaneous blood flow on the back was greater than the forearm (p < 0.01 prick test, p < 0.05 topical application), and that of both sites was greater than the ankle (p < 0.01 prick test, p < 0.05 topical application). There were no significant differences among the different sites in time parameters and no gender variations. As expected, the time required to reach maximum response was shorter for the intradermal method as compared to the topical application on the back (p < 0.001) and forearm (p < 0.05). On the other hand, the time required to decrease to 50% of maximum response was not different for the intradermal and topical methods of histamine application. These blood vessel response observations may provide initial insight into inherent functional differences influencing cutaneous manifestations of endogenous and exogenous diseases.

Administration, Topical↗

PubMed1987

Current source density analysis of frequency coding in the inferior colliculus.

Current source density (CSD) analysis is a technique that provides information about the time course and spatial location of transmembrane currents derived from a laminar collection of evoked potentials. Restrictive conditions for acquisition of evoked potentials are required in order to yield a one-dimensional CSD analysis that is an accurate estimate of synaptic activity. Satisfaction of these conditions was assumed in recordings of tone-burst-evoked potentials along the axis of symmetry (tonotopic) in the inferior colliculus of adult mongolian gerbils. Off-line these data were converted into distance/voltage functions. The second spatial derivatives of these functions gave a family of profiles of the spatial distribution of current source and sink densities at discrete latencies relative to the stimulus. Results indicate a frequency-dependent spatial shift in the evoked current sink of about 280 microns octave. This sink, indicative of local excitatory synaptic drive, is surrounded, both spatially and temporally, by current sources. The spatial extent of excitation as estimated from CSD analysis, compares well quantitatively with predictions from an across-neuron model that is based on single unit data.

Acoustic Stimulation↗

PubMed2000

Tissue-specific expression of a type I adenylyl cyclase rescues the rutabaga mutant memory defect: in search of the engram.

Most attempts to localize physical correlates of memory in the central nervous system (CNS) rely on ablation techniques. This approach has the limitation of defining just one of an unknown number of structures necessary for memory formation. We have used the Drosophila rutabaga type I Ca(2+)/CaM-dependent adenylyl cyclase (AC) gene to determine in which CNS region AC expression is sufficient for memory formation. Using pan-neural and restricted CNS expression with the GAL4 binary transcription activation system, we have rescued the memory defect of the rutabaga mutant in a fast robust spatial learning paradigm. The ventral ganglion, antennal lobes, and median bundle are likely the CNS structures sufficient for rutabaga AC- dependent spatial learning.

Adenylyl Cyclases↗

PubMed2006

Detection of gene copy number changes in CGH microarrays using a spatially correlated mixture model.

MOTIVATION: Comparative genomic hybridization array experiments that investigate gene copy number changes present new challenges for statistical analysis and call for methods that incorporate spatial dependence between sequences along the chromosome. For this purpose, we propose a novel method called CGHmix. It is based on a spatially structured mixture model with three states corresponding to genomic sequences that are either unmodified, deleted or amplified. Inference is performed in a Bayesian framework. From the output, posterior probabilities of belonging to each of the three states are estimated for each genomic sequence and used to classify them. RESULTS: Using simulated data, CGHmix is validated and compared with both a conventional unstructured mixture model and with a recently proposed data mining method. We demonstrate the good performance of CGHmix for classifying copy number changes. In addition, the method provides a good estimate of the false discovery rate. We also present the analysis of a cancer related dataset. SUPPLEMENTARY INFORMATION: http://www.bgx.org.uk/papers.html

Algorithms↗

PubMed2006

Effects of stimulus azimuth and intensity on the single-neuron activity in the auditory cortex of the alert macaque monkey.

It has been hypothesized that the primate auditory cortex is composed of at least two processing streams, one of which is believed to selectively process spatial information. To test whether spatial information is differentially encoded in different auditory cortical fields, we recorded the responses of single neurons in the auditory cortex of alert macaque monkeys to broadband noise stimuli presented from 360 degrees in azimuth at four different absolute intensities. Cortical areas tested were core areas A1 and rostral (R), caudal belt fields caudomedial and caudolateral, and more rostral belt fields middle lateral and middle medial (MM). We found that almost all neurons encountered showed some spatial tuning. However, spatial selectivity measures showed that the caudal belt fields had the sharpest spatial tuning, A1 had intermediate spatial tuning, and areas R and MM had the least spatial tuning. Although most neurons showed their best responses to contralateral space, best azimuths were observed across the entire 360 degrees of tested space. We also noted that although the responses of many neurons were significantly influenced by eye position, eye position did not systematically influence any of the spatially dependent responses that we measured. These data are consistent with the hypothesis that caudal auditory cortical fields in the primate process spatial features more accurately than the core and more rostral belt fields.

Acoustic Stimulation↗

PubMed2006

Building statistical models to analyze species distributions.

Models of the geographic distributions of species have wide application in ecology. But the nonspatial, single-level, regression models that ecologists have often employed do not deal with problems of irregular sampling intensity or spatial dependence, and do not adequately quantify uncertainty. We show here how to build statistical models that can handle these features of spatial prediction and provide richer, more powerful inference about species niche relations, distributions, and the effects of human disturbance. We begin with a familiar generalized linear model and build in additional features, including spatial random effects and hierarchical levels. Since these models are fully specified statistical models, we show that it is possible to add complexity without sacrificing interpretability. This step-by-step approach, together with attached code that implements a simple, spatially explicit, regression model, is structured to facilitate self-teaching. All models are developed in a Bayesian framework. We assess the performance of the models by using them to predict the distributions of two plant species (Proteaceae) from South Africa's Cape Floristic Region. We demonstrate that making distribution models spatially explicit can be essential for accurately characterizing the environmental response of species, predicting their probability of occurrence, and assessing uncertainty in the model results. Adding hierarchical levels to the models has further advantages in allowing human transformation of the landscape to be taken into account, as well as additional features of the sampling process.

Bayes Theorem↗

PubMed2003

Spatiotemporal dynamics of optical molecular motors.

The spatiotemporal dynamics of optical molecular motors is simulated on the basis of a spatially resolved model. A spatially dependent Fokker-Planck model for the molecular motors is linked with Maxwell's wave equation describing the external excitation via a spatially inhomogeneous light field. Simulations show that strong diffusion of the embedding fluent leads to increased motor dynamics while in inhomogeneous ensembles motor clustering may occur. Spatially inhomogeneous optical excitation may provide a means of movement control of the molecular motors.

Adenosine Triphosphate↗

PubMed2003

Soliton emission at a phase-mismatch boundary in a quadratic nonlinear film waveguide.

We report the experimental demonstration of spatial nonlinear beam displacement caused by an interface between periodically modulated and uniform quadratic nonlinearity. We observe intensity- and phase-mismatch-dependent spatial beam displacement at 1548 nm in lithium niobate waveguides. The device has the potential to provide a soliton-emission-based, ultrafast all-optical switch.

Journal Article↗

PubMed2001

Lyme disease in New York State: spatial pattern at a regional scale.

Lyme disease occurs commonly in New York State, but its geographic distribution is heterogeneous. Over each of nine consecutive years, incidence rates from 57 New York State counties were subjected to spatial autocorrelation analysis. Although the epidemic advanced during the study period, the analyses reveal a consistent pattern of spatial dependence. The correlation distance, the distance over which incidence rates covary positively, remained near 120 km over the nine years. A local spatial analysis around Westchester County, a major disease focus, indicated that the global correlation distance matched the extent of the most intense local clustering; statistically weaker clustering extended to 200 km from Westchester. Analyzing the spatial character of the epidemic may reveal the epizootic processes underlying patterns in human infection, and may help identify a spatial scale for regional control of disease.

Humans↗

PubMed2002

Small conductance Ca2+-activated K+ channels modulate synaptic plasticity and memory encoding.

Activity-dependent changes in neuronal excitability and synaptic strength are thought to underlie memory encoding. In hippocampal CA1 neurons, small conductance Ca2+-activated K+ (SK) channels contribute to the afterhyperpolarization, affecting neuronal excitability. In the present study, we examined the effect of apamin-sensitive SK channels on the induction of hippocampal synaptic plasticity in response to a range of stimulation frequencies. In addition, the role of apamin-sensitive SK channels on hippocampal-dependent memory encoding and retention was also tested. The results show that blocking SK channels with apamin increased the excitability of hippocampal neurons and facilitated the induction of synaptic plasticity by shifting the modification threshold to lower frequencies. This facilitation was NMDA receptor (NMDAR) dependent and appeared to be postsynaptic. Mice treated with apamin demonstrated accelerated hippocampal-dependent spatial and nonspatial memory encoding. They required fewer trials to learn the location of a hidden platform in the Morris water maze and less time to encode object memory in an object-recognition task compared with saline-treated mice. Apamin did not influence long-term retention of spatial or nonspatial memory. These data support a role for SK channels in the modulation of hippocampal synaptic plasticity and hippocampal-dependent memory encoding.

Action Potentials↗

PubMed2005

[Study on bias and confounding in 'Spatial Epidemiology'].

OBJECTIVE: To explore the biases and confoundings in Spatial Epidemiological studies. METHODS: Possible bias and confounding and their impact on study results in Spatial Epidemiology were analyzed in given examples. RESULTS: In Spatial Epidemiology, biases related to ascertainment/numerator/denominator induced by the choice of the disease induction/latency period and mis-specification of exposure-disease model, exposure inaccuracy, spatial dependency, significance tests etc. were involved, as well as to ecological, socio-economic confoundings factors. CONCLUSION: The sources of bias in 'Spatial Epidemiology' were both numerous and complex, that might be overestimated or underestimated on the study results. Hence, careful interpretation of such studies was needed.

Bias↗

PubMed2000

Fluorescence lifetime imaging of nuclear DNA: effect of fluorescence resonance energy transfer.

BACKGROUND: DNA fluorescence dyes have been used to study DNA dynamics, chromatin structure, and cell cycle analysis. However, most microscopic fluorescence studies of DNA use only steady-state measurements and do not take advantage of the additional information content of the time-resolved fluorescence. In this paper, we combine fluorescence imaging of DNA with time-resolved measurements to examine the proximity of donors and acceptors bound to chromatin. METHODS: We used frequency-domain fluorescence lifetime imaging microscopy to study the spatial distribution of DNA-bound donors and acceptors in fixed 3T3 nuclei. Over 50 cell nuclei were imaged in the presence of an AT-specific donor, Hoechst 33258 (Ho), and a GC-specific acceptor, 7-aminoactinomycin D (7-AAD). RESULTS: The intensity images of Ho alone showed a spatially irregular distribution due to the various concentrations of DNA or AT-rich DNA throughout the nuclei. The lifetime imaging of the Ho-stained nuclei was typically flat. Addition of 7-AAD decreased the fluorescence intensity and lifetime of the Ho-stained DNA. The spatially dependent phase and modulation values of Ho in the presence of 7-AAD showed that the Ho decay becomes nonexponential, as is expected for a resonance energy transfer (RET) with multiple acceptors located over a range of distances. In approximately 40 nuclei, the intensity and lifetime decrease was spatially homogeneous. In approximately 10 nuclei, addition of 7-AAD resulted in a spatially nonhomogeneous decrease in intensity and lifetime. The RET efficiency was higher in G(2)/M than in G(0/1) phase cells. CONCLUSIONS: Because RET efficiency depends on the average distance between Ho and 7-AAD, data suggest that the heterogeneity of lifetimes and spatial variation of the RET efficiency are caused by the presence of highly condensed regions of DNA in nuclei.

3T3 Cells↗

PubMed2003

Novel ROC-type method for testing the efficiency of multivariate statistical methods in fMRI.

The receiver operating characteristic (ROC) method is a useful and popular tool for testing the efficiency of various diagnostic tests applicable to functional MRI (fMRI) data. Typically, the diagnostic tests are applied on simulated and pseudo-human fMRI data, and the area under the ROC curve is used as a measure of the efficiency of the diagnostic test. The effectiveness of such a method depends on how well the simulated data approximate the real data. For multivariate statistical methods, however, this technique is usually inadequate, as the spatial dependence among voxels is ignored for simulated data. In this work a modified ROC method using real fMRI data with a broader scope is proposed. This method can be applied to most fMRI postprocessing techniques, including multivariate analyses such as canonical correlation analysis (CCA). Also, the relationship of the modified ROC method with the conventional ROC method is discussed in detail.

Algorithms↗

PubMed1999

The effects of NMDA-induced retrohippocampal lesions on performance of four spatial memory tasks known to be sensitive to hippocampal damage in the rat.

Four separate cohorts of rats were employed to examine the effects of cytotoxic retrohippocampal lesions in four spatial memory tasks which are known to be sensitive to direct hippocampal damage and/or fornix-fimbria lesions in the rat. Selective retrohippocampal lesions were made by means of multiple intracerebral infusions of NMDA centred on the entorhinal cortex bilaterally. Cell damage typically extended from the lateral entorhinal area to the distal ventral subiculum. Experiment 1 demonstrated that retrohippocampal lesions spared the acquisition of a reference memory task in the Morris water maze, in which the animals learned to escape from the water by swimming to a submerged platform in a fixed location. In the subsequent transfer test, when the escape platform was removed, rats with retrohippocampal lesions tended to spend less time searching in the appropriate quadrant compared to controls. Experiment 2 demonstrated that the lesions also spared the acquisition of a working memory version of the water maze task in which the location of the escape platform was varied between days. In experiment 3, both reference and working memory were assessed using an eight-arm radial maze in which the same four arms were constantly baited between trials. In the initial acquisition, reference memory but not working memory was affected by the lesions. During subsequent reversal learning in which previously baited arms were now no longer baited and vice versa, lesioned animals made significantly more reference memory errors as well as working memory errors. In experiment 4, spatial working memory was assessed in a delayed matching-to-position task conducted in a two-lever operant chamber. There was no evidence for any impairment in rats with retrohippocampal lesions in this task. The present study demonstrated that unlike direct hippocampal damage, retrohippocampal cell loss did not lead to a general impairment in spatial learning, implying that the integrity of the retrohippocampus and/or its interconnection with the hippocampal formation is not critical for normal hippocampal-dependent spatial learning and memory. This outcome is surprising for a number of current hippocampal theories, and suggests that other cortical as well as subcortical inputs to the hippocampus might be of more importance, and further raises the question regarding the functional significance of the retrohippocampal region.

Animals↗

PubMedDate not supplied

Effects of stress and hippocampal NMDA receptor antagonism on recognition memory in rats.

Exposures to uncontrollable stress have been shown to alter ensuing synaptic plasticity in the hippocampus and interfere with hippocampal-dependent spatial memory in rats. The present study examined whether stress, which impairs hippocampal long-term potentiation (LTP), also affects (nonspatial) hippocampal-dependent object-recognition memory, as tested on the visual paired comparison task (VPC) in rats. After undergoing an inescapable restraint-tailshock stress experience, rats exhibited markedly impaired recognition memory at the 3-h (long) familiarization-to-test phase delay but not at the 5-min (short) delay. In contrast, unstressed control animals showed robust recognition memory (i.e., they exhibited reliable preferences for novel over familiar objects) at both short- and long-delay periods. The impairing effect of stress on long-delay recognition memory was transient because 48 h after undergoing stress experience, animals performed normally at the long delay. Similar to stress, microinfusions of DL-2-amino-5-phosphonovaleric acid (APV), a competitive N-methyl-D-aspartate receptor (NMDAR) antagonist that blocks LTP, into the dorsal hippocampus selectively impaired object-recognition memory at the long-delay period. Together, these results suggest that stress and intrahippocampal administration of APV affect recognition memory by influencing synaptic plasticity in the hippocampus.

Animals↗

PubMed2002

Role of the intramolecular phase in high-harmonic generation.

We study numerically the generation of high-order harmonics by two-center molecules for arbitrary angles between the molecular axis and the laser polarization axis. For fixed angle, the harmonic spectrum exhibits a minimum at a frequency which is independent of the laser parameters. The amplitude of each harmonic is strongly angle dependent, and a pronounced minimum is found at the same angle where a sudden jump in the harmonic phase occurs. By calculating the spatial dependence of the harmonic amplitudes and phases, we are able to explain these effects in terms of interfering contributions from various regions within the molecule.

Journal Article↗

PubMed1994

Ultrasonic B-mode image enhancement based on level-dependent spread functions.

The concept of level-dependent spatial summation is applied to the 2-dimensional amplitude distribution comprising an ultrasonic brightness image. The distribution is convolved with a level-dependent kernel. The size (i.e., extent) of the kernel is inversely proportional to the local signal level. The result is a 2-dimensional distribution of Mach bands, accentuating edges and providing useful information for the reduction of speckle. In addition, a small but powerful extension of the processing scheme is presented that supports global edge enhancement and contrast enhancement. The level of improvement has been quantified in terms of an increase in the lesion signal-to-noise ratio on the order of 60 percent. Only two system-dependent parameters have to be supplied for adjustment. The algorithm is rather insensitive to the exact choice of the parameters, making it quite robust. Since only a limited number of simple operations is required for the processing of a frame, the algorithm is expected to be suitable for real time application.

Image Enhancement↗