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Results for “spatial patterning”

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At least 865 records · Page 48Linked to original sources
PubMed2006

Adaptive feature extraction for EEG signal classification.

One challenge in the current research of brain-computer interfaces (BCIs) is how to classify time-varying electroencephalographic (EEG) signals as accurately as possible. In this paper, we address this problem from the aspect of updating feature extractors and propose an adaptive feature extractor, namely adaptive common spatial patterns (ACSP). Through the weighed update of signal covariances, the most discriminative features related to the current brain states are extracted by the method of multi-class common spatial patterns (CSP). Pseudo-online simulations of EEG signal classification with a support vector machine (SVM) classifier for multi-class mental imagery tasks show the effectiveness of the proposed adaptive feature extractor.

Algorithms↗
PubMed2005

Grey matter changes over time in high risk subjects developing schizophrenia.

Schizophrenia affects approximately 1% of the population and is associated with reductions in brain volume, but when these are first evident is unknown. Magnetic resonance imaging (MRI) has demonstrated abnormalities of brain structure, particularly of the temporal lobes, in schizophrenia. A study of brain structure in individuals destined to develop schizophrenia, before they do so, is crucial to understanding the illness. We used Voxel Based Morphometry (VBM) to map changes in Grey Matter Density (GMD) in 65 young adults at high risk of schizophrenia, for familial reasons, and 19 healthy young adults, over a period of approximately 2 years. All subjects were anti-psychotic naive at both scans. No increases in GMD were found in any of the groups. Within the high-risk group significant declines in GMD were found in the temporal lobes, the right frontal lobe and right parietal lobe. In the control group a decline was found in the right gyrus rectus. No significant differences over time were found between any of the groups. Those individuals at high risk who had transient or isolated psychotic symptoms showed a different spatial pattern of reductions in GMD than those who did not in within group comparisons. In addition, those individuals at high risk who later developed schizophrenia also showed a different spatial pattern of reductions in GMD in the left temporal lobe and right cerebellum, from 2 to 3 years before they were diagnosed. These particular reductions may therefore be able to predict the later onset of schizophrenia.

Adult↗
PubMed2002

Space and the persistence of male-killing endosymbionts in insect populations.

Male-killing bacteria are bacteria that are transmitted vertically through the females of their insect hosts. They can distort the sex ratio of their hosts by killing infected male offspring. In nature, male-killing endosymbionts (male killers) often have a 100% efficient vertical transmission, and multiple male-killing bacteria infecting a single population are observed. We use different model formalisms to study these observations. In mean-field models a male killer with perfect transmission drives the host population to extinction, and coexistence between multiple male killers within one population is impossible; however, in spatially explicit models, both phenomena are readily observed. We show how the spatial pattern formation underlies these results. In the case of high transmission efficiencies, waves with a high density of male killers alternate with waves of mainly wild-type hosts. The male killers cause local extinction, but this creates an opportunity for uninfected hosts to re-invade these areas. Spatial pattern formation also creates an opportunity for two male killers to coexist within one population: different strains create spatial regions that are qualitatively different; these areas then serve as different niches, making coexistence possible.

Animals↗
PubMed1997

Spatial and density effects in evolutionary game theory.

Two models are considered for the study of game dynamics in a spatial domain. Both models are continuous in space and time and give rise to reaction-diffusion equations. The spatial domain is homogeneous but the mobility of the individuals is allowed to depend upon the strategy. The models are analysed for spatial patterns (via a Turing instability) and also for the direction of the travelling wave that replaces one strategy by another. It is shown that the qualitative behaviour of the two models is quite different. When considering the existence of spatial patterns and deciding whether increased mobility is helpful or not, it is shown that the answers depend crucially upon the model equations. Since both models (in the absence of spatial variation) are quite standard, it is clear that considerable care has to be exercised in the formulation of spatial models and in their interpretation.

Animals↗
PubMed1996

Skilled motor performance and working memory in rowers: body patterns and spatial positions.

Previous studies using unfamiliar laboratory tasks (e.g. Smyth & Pendleton, 1990) have shown that working memory for movements to targets external to the body (positional movements) is dissociable from working memory for movements made to recreate specific configurations of body parts (patterned movements). In Experiment 1 this dissociation is replicated using tasks that were adapted for use in Experiment 2. In Experiment 2 the timing of experienced rowers performance of patterned and positional elements of the rowing stroke was selectively disrupted by concurrent performance of patterned and positional memory tasks, respectively. These results suggest that patterned and positional elements of well-practised everyday motor tasks, which involve a complex interaction of the two types of movement, are controlled separately and place dissociable demands on working memory.

Adult↗
PubMed2001

Strain-specific effects of amphetamine on prepulse inhibition and patterns of locomotor behavior in mice.

Several reports describe substantive behavioral differences between strains of mice both at baseline and in response to pharmacological manipulations. For example, mouse strain differences have been reported in prepulse inhibition (PPI) and patterns of locomotor activity, two behavioral processes that are altered by dopamine (DA) agonists such as amphetamine. Here, we characterized acoustic and tactile startle reactivity, acoustic PPI, and both the amounts and spatial patterns of locomotor activity in C57BL/6J, 129SvEv (129S6), and 129SvJ (129X1) mice at baseline and in amphetamine dose-response studies. Because hearing loss is common in numerous strains of mice, we also assessed cross-modal PPI using a light prepulse with an airpuff startle stimulus. The results establish that these three inbred strains of mice display both intra- and cross-modal PPI, and that amphetamine decreases PPI and startle reactivity in a dose-, sensory modality-, and strain-specific manner. Furthermore, the amount of locomotor activity and the spatial pattern of motor sequences are altered differentially after treatment with amphetamine in C57BL/6J and 129X1 mice, but not in 129S6 mice. Given that amphetamine releases presynaptic DA, these findings are consistent with the role of DA in the modulation of PPI and motor patterns in mice. These findings highlight the importance of selecting appropriate strains of mice for behavioral, pharmacological, and genetic studies.

Acoustic Stimulation↗
PubMed2001

Neural coding mechanisms underlying perceived roughness of finely textured surfaces.

Combined psychophysical and neurophysiological studies have shown that the perceived roughness of surfaces with element spacings of >1 mm is based on spatial variation in the firing rates of slowly adapting type 1 (SA1) afferents (mean absolute difference in firing rates between SA1 afferents with receptive fields separated by approximately 2 mm). The question addressed here is whether this mechanism accounts for the perceived roughness of surfaces with element spacings of <1 mm. Twenty triangular and trapezoidal gratings plus a smooth surface were used as stimulus patterns [spatial periods, 0.1-2.0 mm; groove widths (GWs), 0.1-2.0 mm; and ridge widths (RWs), 0-1.0 mm]. In the human psychophysical studies, we found that the following equation described the mean roughness magnitude estimates of the subjects accurately (0.99 correlation): 0.2 + 1.6GW - 0.5RW - 0.25GW(2). In the neurophysiological studies, these surfaces were scanned across the receptive fields of SA1, rapidly adapting, and Pacinian (PC) afferents, innervating the glabrous skin of anesthetized macaque monkeys. SA1 spatial variation was highly correlated (0.97) with human roughness judgments. There was no consistent relationship between PC responses and roughness judgments; PC afferents responded strongly and almost equally to all of the patterns. Spatial variation in SA1 firing rates is the only neural code that accounts for the perceived roughness of surfaces with finely and coarsely spaced elements. When surface elements are widely spaced, the spatial variation in firing rates is determined primarily by the surface pattern; when the elements are finely spaced, the variation in firing rates between SA1 afferents is determined by stochastic variation in spike rates.

Action Potentials↗
PubMed2006

Coding and synaptic processing of sensory information in the glomerular layer of the olfactory bulb.

Input from olfactory receptor neurons is first organized and processed in the glomerular layer of the olfactory bulb. Olfactory glomeruli serve as functional units in coding olfactory information and contain a complex network of synaptic connections. Odor information has long been thought to be represented by spatial patterns of glomerular activation; recent work has, additionally, shown that these patterns are temporally dynamic. At the same time, recent advances in our understanding of the glomerular network suggest that glomerular processing serves to temporally sharpen these dynamics and to modulate spatial patterns of glomerular activity. We speculate that odor representations and their postsynaptic processing are tuned to and shaped by the sniffing behavior of the animal.

Animals↗
PubMed2006

Investigating gene expression: in situ hybridization and reporter genes.

Coordinated cell type differentiation is essential for morphogenesis during Dictyostelium development. The specification of different cell types and the regulation of temporal and spatial patterns of expression of cell type-specific genes are important problems currently being addressed in many laboratories. Besides, determination of gene expression patterns provides significant information in the characterization of developmental mutants. Cell type-specific probes and well characterized promoters are available that allow the identification of most cell types during Dictyostelium development. Expression patterns can be studied by whole-mount in situ messenger RNA (mRNA) detection and by the use of reporter genes under the control of specific promoters. The most common in situ hybridization technique, based on nonradioactive ribo-probes that are hybridized to fixed whole-mounts prepared at different developmental stages, is described. Several reporter genes have been used to characterize gene expression patterns and to determine functional promoter elements. The lacZ gene, coding for the beta-galactosidase enzyme, is the reporter most frequently used in Dictyostelium because both temporal- and spatial-patterns of expression can be easily determined. Generally used beta-galactosidase detection methods are described.

Animals↗
PubMed2003

Genetic analysis of spatial foraging patterns and resource sharing in bumble bee pollinators.

Conservation biologists, evolutionary ecologists and agricultural biologists require an improved understanding of how pollinators utilize space and share resources. Using microsatellite markers, we conducted a genetic analysis of space use and resource sharing at several spatial scales among workers of two ecologically dissimilar bumble bee species (Bombus terrestris and B. pascuorum) foraging in an urban landscape (London, UK). At fine scales, the relatedness of workers visiting small patches of flowers did not differ significantly from zero. Therefore, colonies shared flower patches randomly with other colonies, suggesting that worker scent-marks deterring visits to unrewarding flowers have not evolved as signals benefiting nestmates. To investigate space use at intermediate scales, we developed a program based on Thomas & Hill's maximum likelihood sibship reconstruction method to estimate the number of colonies utilizing single sites. The average number of colonies (95% confidence limits) sending workers to forage at sites of approximately 1 ha in area was 96 colonies (84-118) in B. terrestris and 66 colonies (61-76) in B. pascuorum. These values are surprisingly high and suggested that workers travelled far from their colonies to visit the sites. At the landscape scale, there was little or no genetic differentiation between sites. We conclude that urban habitats support large bumble bee populations and are potentially valuable in terms of bumble bee conservation. In addition, bumble bee-mediated gene flow in plants is likely to occur over large distances and plant-bumble bee conservation requires landscape-scale action.

Alleles↗
PubMed1982

Pattern formation in morphogenesis. Analytical treatment of the Gierer-Meinhardt model on a sphere.

We first treat the Gierer-Meinhardt equations by linear stability analysis to determine the critical parameter, at which the homogeneous distributions of activator and inhibitor concentrations become unstable. We find two types of instabilities: one leading to spatial pattern formation and another one leading to temporal oscillations. We consider the case where two instabilities are present. Using the method of generalized Ginzburg-Landau equations introduced earlier we then analyze the nonlinear equations. As we are mainly interested in spatial pattern formation on a sphere we consider the problem under an appropriate constraint. Combining the two occurring solutions we find patterns well-known in biology, such as a gradient system and temporal oscillations.

Animals↗
PubMed2006

Chinmo and neuroblast temporal identity.

Although spatial patterning during embryonic development is well characterized, a corresponding framework for temporal patterning has not been established. In this issue, Zhu et al. (2006) identify the Chinmo protein as conferring temporal identity on the neural progeny of Drosophila neuroblasts, revealing appealing parallels with spatial patterning.

Animals↗
PubMed1986

Relation of olfactory EEG to behavior: time series analysis.

Oscillatory electroencephalographic bursts were measured from 64 electrodes implanted on the olfactory bulbs of rabbits. Oscillatory bursts that occurred before and during presentation of odorant conditioned stimuli (CSs) were selected in brief segments. Comparisons between the 64 traces and their spectra showed that, despite amplitude differences between channels, every burst had a common waveform over the entire array. The spectra showed 2 to 5 distinct peaks in each burst. Each trace was fitted with the sum of 5 cosines to express the burst in ten 8 X 8 matrices of amplitude and phase values at its peak frequencies. Two types of burst were identified. Those with dominant frequencies greater than 55 Hz had one narrow dominant spectral peak and reproducible spatial patterns of its amplitude within subgroups of bursts relating to control and odorant CS conditions. Those with dominant frequencies less than 55 Hz were disorderly; their spectra were broad, and their spatial patterns of amplitude did not reproduce within subgroups. A behavioral assay showed that the high- and not the low-frequency bursts contained odor-specific information.

Animals↗
PubMed2003

Precursor tissue analogs as a tissue-engineering strategy.

Natural tissues are composed of functionally diverse cell types that are organized in spatially complex arrangements. Organogenesis of complex tissues requires a coordinated sequential transformation process, with individual stages involving time-dependent expression of cell-cell, cell-matrix, and cell-signal interactions in three dimensions. The common theme of temporal-spatial patterning of these cellular interactions is also observed in other physiological processes, such as growth and development, wound healing, and tumor migration. The "precursor tissue analog" (PTA) applies the temporal-spatial patterning theme to tissue engineering. The goal of PTA in tissue engineering is not to fabricate the final transplantable tissue but rather to guide the dynamic organization, maturation, and remodeling leading to the formation of normal and functional tissues. We describe the critical design principles of PTA. First, structural, mechanical, and physiological requirements of the PTA as a temporary scaffold must be met by a fabrication method with flexibility. The fabrication potential incorporating biological materials such as living cells and plasmid DNA has been addressed. Second, the PTA concept is considered suitable for future tissue engineering in light of the use of undifferentiated stem cells, and may possess a capability to guide stem cells toward diverse differentiation characteristics in situ. To this end, the behavior of the engineered cell and tissue must be monitored in detail. The development of a practical phenotype monitoring system such as a DNA microarray may be integral to the fabrication strategies of PTA. Third, the microtopographical and microenvironmental control on the liquid-solid interaction may lead to a critical design for PTA to provide soluble factors, nutrients, and gases to the cells embedded within the scaffold. We suggest that the level set numerical simulation method may be utilized to engineer the consistent circulation of bioactive liquid throughout the PTA microenvironment.

Animals↗
PubMedDate not supplied

Morphogenesis in germinating Fusarium graminearum macroconidia.

Fusarium graminearum (teleomorph Gibberella zeae) is a significant pathogen of wheat and corn. F. graminearum forms multicellular macroconidia that play an important role in dissemination of the disease. The spatial pattern of morphogenesis in germinating macroconidia is described. Germ tubes preferentially emerge from the apical cells in a bipolar pattern that appears to be common to filamentous fungi. Chitin deposition occurs at two locations: the spore apices and cortical regions of macroconidial cells that subsequently produce a germ tube. The spatial pattern of morphogenesis requires the presence of functional microtubules, which may be responsible for the transport of key polarity factors to specific sites. These observations suggest that F. graminearum possesses a regulatory system that marks germ tube emergence sites. Perturbation of this system may represent an effective approach for inhibiting colonization of host plant surfaces.

Cell Polarity↗
PubMed1991

Ultrastructural and morphometric analysis of the separation of two thigh muscles in the chick.

Limb muscles separate from one another in a complex but highly stereotyped sequence and spatial pattern. The process of separation is characterized by the progression of a region of increased extracellular space, the cleavage zone, along the proximodistal axis between the individual muscle anlagen. We analyzed ultrastructurally the muscles and cleavage zone during the separation of two representative muscles, the developing sartorius and iliotibialis in the chick thigh, to establish an accurate baseline for an analysis of the mechanisms of separation. Comparisons of the morphology and distribution of cells before and after separation show no evidence that muscles became separated by the massive influx of an exterior cell population; if populations invade the cleavage zone, they are small. We do find characteristic transitions within the cell population of the cleavage zone in situ that could accomplish cleavage without invoking massive cell movements. These progressive transitions within the cleavage zone include a loss of close cell-cell interactions, an increase in extracellular space, the assumption of a more stellate morphology by mesenchyme cells, and a gradual alteration in the composition of the extracellular matrix from one typical of early muscle to one typical of loose connective tissue. Myotubes do differentiate between the incipient muscles, ruling out the possibility that the location where muscles will separate is defined by sites where myotubes fail to differentiate. Instead, the myotubes in the cleavage zone gradually diminish in number and appear to be specifically recognized and removed from the cleavage zone by phagocytes. We suggest that the transitions within the cleavage zone, including the loss of muscle cells, are a result of the progressive differentiation of loose connective tissue. If so, then the spatial pattern and process of cleavage is a consequence of spatially programmed cell differentiation.

Animals↗
PubMed2000

The effect of nicotine on gene expression during spine fusion.

STUDY DESIGN: A rabbit model of posterolateral spine fusion was used to investigate the effect of nicotine on cytokine expression during spine fusion. OBJECTIVES: To determine the effects of nicotine on the known gene expression pattern of bone morphogens and related proteins expressed during spine fusion. SUMMARY OF BACKGROUND DATA: The mechanism by which nicotine increases the pseudarthrosis rate of spine fusion is unknown. Recently, a distinct temporal and spatial pattern of cytokine expression during bone formation has been described. The authors hypothesized that nicotine would alter this known pattern, thereby revealing the mechanism by which nicotine exerts its effect. METHODS: Twenty-eight New Zealand White rabbits underwent posterolateral spine fusion with autogenous bone graft. Fourteen rabbits received systemic nicotine by a miniosmotic pump. Fusions were harvested at 0, 2, 5, and 7 days and 2, 3, and 4 weeks after arthrodesis. Specimens were divided into the outer zones adjacent to the transverse processes and the central zones between the transverse processes. Gene expression of type I and II collagen, bone morphogenic protein-2, -4, and -6 and basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) was then measured at each time point in each of the two zones. RESULTS: Nicotine inhibited expression of all cytokines measured, mainly in the central zone. However, the previously described temporal and spatial patterns of expression were preserved. CONCLUSIONS: Nicotine inhibits expression of a wide range of cytokines, including those associated with neovascularization and osteoblast differentiation. Therefore, the effects of nicotine appear to involve more than just local vasoconstriction.

Animals↗
PubMedDate not supplied

Genetic structure of human populations in the British Isles.

Spatial patterns were studied for 36 allele frequencies representing 14 genetic systems (blood antigens, enzymes and serum proteins) in the United Kingdom and Irish Republic. The total number of data points over all systems and localities is 331. Patterns of genetic variation in space are graphically represented by one-dimensional and directional correlograms, and by interpolated allele-frequency surfaces. The data surfaces were examined by the various techniques of spatial autocorrelation analysis. Zones of rapid change across allele surfaces were discovered by the wombling method. Six allele frequency surfaces from four genetic systems exhibit significant spatial patterns. Only one pattern (IO; in the ABO system) may be described as purely clinal in an east-west direction; another (IB; in ABO) approximates a cline or at least north-south differentiation. A method was developed for testing the direction of maximal genetic autocorrelation. Two previously unrecorded patterns for the British Isles, north-south gradients for Rhesus and P, were detected. Twelve zones of rapid genetic change were discovered; some of these seem to reflect maritime and montane physical barriers as well as long-held cultural and linguistic differences, particularly between early Germanic and Celtic speakers. Moreover, some appear to reflect past historic events such as the invasions of Anglo-Saxons and Anglo-Normans.

ABO Blood-Group System↗