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At least 1,603 records · Page 89Linked to original sources
PubMed1997

Is unilateral spatial neglect a single phenomenon? A comparative study between exploratory-motor and visual-counting tests.

The aim of this study is to report the preliminary findings of a traditional battery of tests and our original battery capable of assessing the presence of components and extent of lesions in patients with unilateral spatial neglect. Thirty patients who had unilateral spatial neglect with a stroke in the right hemisphere were assessed for unilateral spatial neglect on exploratory-motor (E-M) tasks, visual-counting (V-C) tasks, and traditional neglect batteries at least 4 weeks after the onset. Other neuropsychological tests and computed tomography were also performed to investigate the relationship with neglect. A factor analysis showed that our tasks loaded significantly on three factors. E-M neglect was found in 16 patients, and V-C neglect in 22 patients with unilateral spatial neglect. There were high correlations between E-M neglect and motor paralysis, word fluency, backward digit span and motor impersistence. There were high correlations between V-C neglect and visual-field defect, line bisection, line cancellation and figure copying. Lesions in the frontal lobe, caudate, insula, and anterior portion of the paraventricular white matter were commonly associated with E-M neglect. Lesions in the occipital lobe were also associated with V-C neglect. We suggest that unilateral neglect is not a single phenomenon, but rather involves several different components. We propose that E-M and V-C tasks are useful methods for evaluating the extent of lesions in patients with unilateral spatial neglect.

Adult↗
PubMed2000

Assessment of mitochondrial polarization status in living cells based on analysis of the spatial heterogeneity of rhodamine 123 fluorescence staining.

The mitochondrial membrane potential (psimito) is an important parameter not only of mitochondrial but also of cellular status. Prolonged mitochondrial depolarization is associated with various forms of neuronal death. Assessment of mitochondrial depolarization can take advantage of the specific properties of the lipophilic dyes that distribute in a potentiometrically determined ratio across membranes. Using conventional imaging, we showed that rhodamine 123 accumulated in the mitochondria, generating a highly heterogeneous pattern of spatial distribution of fluorescence across the cell body. Collapse of the psimito following exposure to a protonophore, carbonylcyanide p-chloromethoxyphenylhydrazone (CCCP), released rhodamine 123 from mitochondria into the cytosol. Under acutely changed conditions, this increased the overall intensity of the fluorescence signal and significantly decreased the degree of spatial heterogeneity of the signal. If mitochondrial depolarization was sustained chronically, the intensity of the signal decreased, but the increase in the spatial homogeneity of the fluorescent signal was maintained. Image analysis showed that the level of spatial heterogeneity of the signal can be assessed by calculating, for each individual neurone, the spread of pixel intensities values around the mean. This spread is defined by the coefficient of variation (CV), which is a measure of the standard deviation normalized to the average, and was inversely related to mitochondrial depolarization measured under different conditions. Thus, the degree of spatial heterogeneity of the rhodamine 123 signal measured from a neurone is a reliable indicator for the assessment of mitochondrial depolarization and can be used in experiments to monitor psimito over shorter or longer periods.

Animals↗
PubMed1998

Spatial information with pictures and words in visual short-term memory.

In a delayed matching task, the influence of spatial congruence between study and test on visual short-term memory for geometric figures and words was investigated. Subjects processed series of pictures which showed three words or three geometric figures arranged as rows or as triangular configurations. At test, the elements were presented in the identical or in the alternative configuration as at study. In the non-matching case, one of the studied elements was exchanged. The delay was 5 s. Subjects judged whether the elements were the same as during study, independent of their configuration. In Exp. 1, pictures of figures and words were mixed within one list. For both modalities, the response times were longer if the configuration at test was incongruent to the one at study. This contradicts the results of Santa, who observed effects of spatial congruency for figures, but not for words. In Exp. 2 we therefore presented the same material as in Exp. 1, but now the lists were modality-pure, as in the experiment of Santa--i.e., words and figures were shown in different lists. This time, spatial incongruency impaired recognition of the figures, but not recognition of the words. These results show that in a non-verbal context, isolated visually presented words are spatially encoded as non-verbal stimuli (figures) are. However, the word stimuli are encoded differently if the task is a pure verbal one. In the latter case, spatial information is discarded.

Humans↗
PubMed2003

Landscape effects on temporal and spatial properties of vole population fluctuations.

Populations of northern small rodents have previously been observed to fluctuate in spatial synchrony over distances ranging from tens to hundreds of kilometers between sites. It has been suggested that this phenomenon is caused by common environmental perturbations, mobile predators or dispersal movements. However, very little focus has been given to how the physical properties of the geographic area over which synchrony occurs, such as landscape composition and climate, affect spatial population dynamics. This study reports on the spatial and temporal properties of vole population fluctuations in two areas of western Finland: one composed of large interconnected areas of agricultural farmland interspersed by forests and the other highly dominated by forest areas, containing more isolated patches of agricultural land. Furthermore, the more agricultural area exhibits somewhat milder winters with less snow than the forested area. We found the amplitude of vole cycles to be essentially the same in the two areas, suggesting that the relative amount of predation on small rodents by generalist versus specialist predators is similar in both areas. No seasonal differences in the timing of synchronization were observable for Microtus voles, whereas bank vole populations in field habitats appeared to become synchronized primarily during winter. Microtus populations in field habitats exhibited smaller spatial variation and a higher degree of synchrony in the more continuous agricultural landscape than in the forest-dominated landscape. We suggest that this inter-areal difference is due to differences in the degree of inter-patch connectivity, with predators and dispersal acting as the primary synchronizing agents. Bank vole populations in field habitats were more synchronized within the forest-dominated landscape, most likely reflecting the suitability of the inter-patch matrix and the possibility of dispersal. Our study clearly indicates that landscape composition needs to be taken into account when describing the spatial properties of small rodent population dynamics.

Analysis of Variance↗
PubMed2005

Density dependence, spatial scale and patterning in sessile biota.

Sessile biota can compete with or facilitate each other, and the interaction of facilitation and competition at different spatial scales is key to developing spatial patchiness and patterning. We examined density and scale dependence in a patterned, soft sediment mussel bed. We followed mussel growth and density at two spatial scales separated by four orders of magnitude. In summer, competition was important at both scales. In winter, there was net facilitation at the small scale with no evidence of density dependence at the large scale. The mechanism for facilitation is probably density dependent protection from wave dislodgement. Intraspecific interactions in soft sediment mussel beds thus vary both temporally and spatially. Our data support the idea that pattern formation in ecological systems arises from competition at large scales and facilitation at smaller scales, so far only shown in vegetation systems. The data, and a simple, heuristic model, also suggest that facilitative interactions in sessile biota are mediated by physical stress, and that interactions change in strength and sign along a spatial or temporal gradient of physical stress.

Analysis of Variance↗
PubMed2004

Scalp field potentials of human pain: spatial effects and temporal relation in finger stimulation.

In the present study, the spatial extent and temporo-spatial correlations of the human brain responses were investigated by electrically stimulating thumb (D1) and little finger (D5) under painful and non-painful intensity levels. High-density (124-ch) somatosensory evoked potentials (SEPs) were recorded (-50 to +450 ms) from 15 healthy male volunteers. Early (0-50 ms), and late phases (150-450 ms) of the responses were analyzed. Peak stages 33 ms, 42 ms, 210 ms, 328 ms for D1; and 33 ms, 44 ms, 240 ms, 350 ms for D5 were isolated from a compressed waveform; the relationships within stages and phases were investigated using topography, Focal maximum Amplitude (FA, single central site at 0.2 cm2) and Area Magnitude (AM, summated FA and amplitudes of neighboring four sites in a region of nearly 9.9 cm2 area). In the early phase, the response of FA at 33 ms was significantly higher during painful than non-painful stimulation for both D1 and D5. In the late phase D1 (210 ms and 328 ms), and D5 (240 ms and 350 ms) the spatial areas of activation were significantly enlarged from non-painful to painful stimulation. For temporo-spatial relationship, D1 at 33 ms of early phase showed a significant correlation between the negative maximal site (sink) and the positive maximal site (source) under both non-painful and painful stimulations. For the late phase, the AM potentials at N2 correlated with that of P2 for both D1 and D5 under painful stimulation. The focal effects in FA of contralateral early potential indicates a shallow dipole in the primary somatosensory area of SI, while the large spatial extent in AM indicates a deep dipole of the putative cingulum activation under painful stimulation. No correlation between early and late activities implied that both activations are operated independently at the early SI and late cingulate processing of evoked pain.

Adult↗
PubMed2006

Use of the spatial scan statistic to identify geographic variations in late stage colorectal cancer in California (United States).

OBJECTIVES: To identify geographic variations in colorectal cancer by stage at diagnosis in California using a descriptive analysis coupled with a spatial analysis and to discuss methodological considerations concerning the spatial statistical method. METHODS: We analyzed 59,076 colorectal cancer cases diagnosed in California from 1996 to 2000 by logistic regression and by a spatial scan statistic to identify areas with a higher and lower relative risk of late-stage colorectal cancer. RESULTS: In California, 57% of overall cases of colorectal cancer were diagnosed at a late stage. Californians diagnosed with late-stage colorectal cancer were more likely to be Hispanic and living in areas of lower socioeconomic status. The spatial scan identified two areas where the observed number of late-stage cancer was different than the number expected from the distribution in the rest of the state. CONCLUSIONS: Spatial scan analyses can complement descriptive statistics, but results must be interpreted with consideration of factors that affect the ability to detect meaningful differences such as the number of events observed, accuracy in geocoding rural versus urban addresses, and the difficulty of adjusting for covariates.

Aged↗
PubMed2006

Spatial variability of salinity and alkalinity of a field having salination risk in semi-arid climate in northern Turkey.

Spatial variability of salinity and alkalinity is important for site-specific management since they are the most important factors influencing soil quality and agricultural production. The objectives of this study were to analyze spatial variability in salinity and alkalinity and some soil properties affecting salinity and alkalinity, using classical statistics and geostatistical methods, in an irrigated field with low-quality irrigation water diverted from drainage canals. A field of 5 da was divided into 10 m x 10 m grids (5 lines in the east-west direction and 10 lines in the north-south direction). The soil samples were collected from three depths (0-30, 30-60 and 60-90 cm) at each grid corner. The variation coefficients of OM and sand contents were higher than other soil properties. OM had the maximum variability, with a mean of 1.63% at 0-30 cm depth and 0.71% at 30-60 cm depth. Significant correlations occurred between ESP, EC and each of Ca, Mg, K and CaCO(3) contents of the soils (p<0.01). Experimental semivariograms were fitted to spherical and gaussian models. All geostatistical range values were greater than 36 m. The soil properties had spatial variability at small distances at 60-90 cm depth. EC was variable within short distances at 30-60 cm depth. The nugget effect of ESP increased with soil depth. Kriged contour maps revealed that soils had a salinisation and alkalisation tendency at 60-90 cm depth based on spatial variance structure of the EC and ESP values. Spatial variability in EC and ESP can depend on ground water level, quality of irrigation water, and textural differences.

Desert Climate↗
PubMedDate not supplied

Genetic spatial clustering: significant implications for conservation of wild soybean (Glycine soja: Fabaceae).

Knowledge of spatial patterns of genetic variation within populations of wild relative species has significant implications with respect to sampling strategies for ex situ and in situ conservation. To study spatial genetic structure of wild soybean (Glycine soja Sieb. et Zucc.) at the fine scale, three natural populations in northern China were analyzed using inter-simple sequence repeat (ISSR) fingerprints for estimating kinship coefficients. A regression analysis of kinship coefficients against spatial distances revealed that individuals occurring close together tended to be more genetically related. The Sp statistic further indicated a comparable spatial pattern among the three wild soybean populations with similar Sp values (mean = 0.0734, varied from 0.0645 to 0.0943) detected across the three populations. Genetic patches were on average ca. 20 m in size, and the effective neighborhood sizes varied between 10 and 15 m. The spatial genetic structure evident in the wild soybean populations may be attributed to the restricted seed dispersal and predominant inbreeding mating system of this species. The detection of family structure in the populations of wild soybean has a significant implication for the effective conservation of the important genetic resources.

Breeding↗
PubMed2005

Spatial cognition in autism spectrum disorders: superior, impaired, or just intact?

The profile of spatial ability is of interest across autism spectrum disorders (ASD) because of reported spatial strengths in ASD and due to the recent association of Asperger's syndrome with Nonverbal Learning Disability. Spatial functions were examined in relation to two cognitive theories in autism: the central coherence and executive function (EF) theories. Performance on spatial tasks, EFs, and global/local processing was compared in children with ASD and controls. While the ASD group had faster reaction times on the Embedded Figures task, spatial performance was intact, but not superior, on other tasks. There was no evidence for impairments in EF or in processing global/local information, therefore contradicting these two theories. The implications of these results for these two theories are discussed.

Adolescent↗
PubMed2006

Dynamic survival models with spatial frailty.

In many survival studies, covariates effects are time-varying and there is presence of spatial effects. Dynamic models can be used to cope with the variations of the effects and spatial components are introduced to handle spatial variation. This paper proposes a methodology to simultaneously introduce these components into the model. A number of specifications for the spatial components are considered. Estimation is performed via a Bayesian approach through Markov chain Monte Carlo methods. Models are compared to assess relevance of their components. Analysis of a real data set is performed, showing the relevance of both time-varying covariate effects and spatial components. Extensions to the methodology are proposed along with concluding remarks.

Bayes Theorem↗
PubMed2006

Nerve growth factor differentially affects spatial and recognition memory in aged rats.

In rats, object discrimination depends on the integrity of the cholinergic system, thus it could be expected that nerve growth factor (NGF) can improve the behavior in aged subjects. The interactive effect of age and cholinergic improvement was assessed behaviorally in young and aged rats. Animals were injected by infusion of NGF into the lateral ventricles and they were tested in two behavioral tasks: an object-location and an object-recognition task. Spatial and recognition memory were assessed in an open field containing five different objects. Rats were submitted to six consecutive sessions. Both age-groups showed comparable habituation of exploratory response in Session 1-4. Discrimination index (DI) was calculated to assess responses to spatial change in Session 5 and object change in Session 6. Control young and aged rats were able to discriminate between familiar and novel object, however DI was lower in aged rats. Treatment with NGF induced decline of object discrimination in both age-groups. Different results were obtained in spatial displacement test. NGF was able to improve spatial memory in aged rats, but had no effect in young controls. These data confer on NGF potential role in improving spatial but not episodic memory in aged rats.

Aging↗
PubMed2007

A method for quantitative analysis of spatially variable physiological processes across leaf surfaces.

Many physiological processes are spatially variable across leaf surfaces. While maps of photosynthesis, stomatal conductance, gene expression, water transport, and the production of reactive oxygen species (ROS) for individual leaves are readily obtained, analytical methods for quantifying spatial heterogeneity and combining information gathered from the same leaf but with different instruments are not widely used. We present a novel application of tools from the field of geographical imaging to the multivariate analysis of physiological images. Procedures for registration and resampling, cluster analysis, and classification provide a general framework for the analysis of spatially resolved physiological data. Two experiments were conducted to illustrate the utility of this approach. Quantitative analysis of images of chlorophyll fluorescence and the production of ROS following simultaneous exposure of soybean leaves to atmospheric O3 and soybean mosaic virus revealed that areas of the leaf where the operating quantum efficiency of PSII was depressed also experienced an accumulation of ROS. This correlation suggests a causal relationship between oxidative stress and inhibition of photosynthesis. Overlaying maps of leaf surface temperature and chlorophyll fluorescence following a photoinhibition treatment indicated that areas with low operating quantum efficiency of PSII also experienced reduced stomatal conductance (high temperature). While each of these experiments explored the covariance of two processes by overlaying independent images gathered with different instruments, the same procedures can be used to analyze the covariance of information from multiple images. The application of tools from geographic image analysis to physiological processes occurring over small spatial scales will help reveal the mechanisms generating spatial variation across leaves.

Algorithms↗
PubMed1981

The spatial and temporal organisation of motion perception units in human vision.

Measurements of threshold illumination levels for detection of retinally non-localised moving targets show that detection of a moving target is influenced by both the spatial and the temporal modulation of the background field. The temporal response characteristics obtained from these measurements are similar to those obtained from experiments on detection of temporal flicker. Experiments with spatially modulated background fields reveal visual mechanisms with spatial properties which are essentially independent of many stimulus parameters. The response amplitude of the spatial filter which characterises these mechanisms increases linearly as a function of background contrast and is independent of the relative orientation between the background structure and the direction of target movement. These properties are used to compute the two-dimensional spatial characteristics of mechanisms involved in the detection of moving targets.

Adult↗
PubMed1995

Gender-, side- and site-dependent variations in human perioral spatial resolution.

Twenty-eight right-handed, young adults participated in a sensory testing experiment to evaluate spatial resolution at 10 positionally matched sites on the right- and left-hand sides of the face. An adaptive psychophysical (i.e. tracking) procedure was used to estimate the threshold spatial separation for perceiving two points of contact at each site. Estimates of the threshold at one site on both sides of the face were also obtained with a method-of-limits procedure similar to that employed for clinical evaluation of patients. In addition, each individual was asked to rate (i) his(her) overall facial sensitivity to touch and (ii) the degree to which he(she) could discern subtle changes in lip, cheek and chin position during speech, chewing and facial expression. Analysis of the estimates of the threshold separation obtained with the tracking procedure revealed a significant effect of gender (p < 0.04) and of site (p < 0.001). Females were more spatially sensitive than males: average threshold separations were 1.55 mm less. Most notably, the threshold increased ninefold with distance posterolaterally from the oral opening. The vermilion of the upper lip was the most spatially sensitive site (population geometric mean = 2.4 mm) and the preauricular skin the least spatially sensitive site (20.9 mm). Significant effects of side and of interactions among gender, side and site were not observed. The estimates obtained with the method-of-limits procedure were very similar to those obtained with the tracking procedure: the latter were 0.67 mm less on the average. Individuals' ratings of overall facial sensitivity to touch were similar for males and females (p > 0.70). Females, however, reported greater ability to discern subtle changes in lip, cheek and chin position than males (p < 0.03). The ratings of this sensory function correlated negatively with the estimates of the threshold separation on the vermilion of the upper lip (p < 0.03).

Adaptation, Physiological↗
PubMed1984

Functional analysis of spatially discriminative neurons in prefrontal cortex of rhesus monkey.

The present study addresses the question of whether prefrontal neurons that exhibit spatially selective patterns of discharge during the delay period in spatial delayed-response tasks code a mnemonic event. To examine this question, rhesus monkeys were trained to perform two variants of the classical spatial delayed-response task in both of which a delay intervened between cue presentation and response and the discriminative stimulus had to be recalled at the moment of response. They were also trained to perform two control tasks in which memory was not required since cues present throughout the delay informed the monkey of the correct response. Extracellular recordings were obtained from 192 neurons located in and around the principal sulcus of the frontal lobe during performance of both control and delay tasks. Comparison of the same neuron's activity across the 4 task conditions revealed a class of neuron that displayed spatially discriminative activity in the delay period only during delayed-response tasks and not during the same period of the control tasks. These neurons are candidates for units engaged in a central mnemonic process. Other neurons either exhibited similar activity in the delay period of control and delayed-response tasks or stronger discriminative behavior during this period in control tasks than in delayed response tasks. We conclude that delay-related spatially discriminative neurons found in the prefrontal association cortex are diversified and that certain of them play a specific role in mnemonic coding.

Animals↗
PubMed1991

Intrahippocampal transplants of septal cholinergic neurons: high-affinity choline uptake and spatial memory function.

Recent studies have demonstrated that intrahippocampal cholinergic septal grafts can ameliorate deficits in spatial memory function and hippocampal cholinergic neurochemical activity in animals with disruptions of the septohippocampal system. However, no study has determined if the restoration of spatial memory function is correlated to the restoration of cholinergic activity, as measured by high-affinity choline uptake (HACU). The present study was designed to determine if such a correlation between behavioral and neurochemical restoration exists. Male Sprague-Dawley rats received either sham lesions (SHAM), bilateral lesions of the septohippocampal pathway (LES), or bilateral lesions along with intrahippocampal septal grafts (SG). After 8 months, rats were tested for their ability to perform spatial reference, spatial navigation and working memory tasks. Upon completion of the behavioral testing, neurochemical activity of the hippocampus was measured by HACU. The results indicate that animals in the SG group had significantly higher behavioral scores and hippocampal HACU rates than animals in the LES group. Regression analysis indicates that a significant correlation exists between performance on each behavioral task and HACU rates. These results demonstrate that hippocampal cholinergic activity, as measured by HACU, correlates significantly with performance on tests of spatial memory function.

Animals↗
PubMed1991

Spatial representation of objects in the young blind child.

Four experiments investigated the young blind child's ability to discover, construct and transform representations of objects, in particular those that preserve the spatial relationships among object parts. Experiment 1 showed that three 18-36-month-old blind children systematically explored novel objects using distinctive haptic manipulations linked to novel shape versus texture. Experiments 2, 3 and 4 pursued a single blind child's ability to represent and transform the spatial configurations of objects. By 2 1/2 years, this child was able to rapidly recognize and identify familiar geometric figures following brief exploration (Experiment 2). By 3 years, she was able to recognize novel objects under 180 degree rotations when their configurations differed from distractors only in the spatial relationships holding among object parts (Experiment 3). At this age, she was also able to infer the locations corresponding to spatial parts of novel objects (the top, bottom, front, back and side) when the objects were upright or rotated, defined only by the location of a single "anchor" term that established their orientation (Experiment 4). In all cases, the blind child's performance was quite similar to that of sighted controls. The results indicate that visual experience is not necessary for the early natural emergence of the capacity to represent and transform spatial descriptions of objects.

Attention↗