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PubMed2004

Spatial and temporal analysis of the local response to wounding in Arabidopsis leaves.

We studied the local response to wounding in Arabidopsis thaliana leaves using a two-step microarray analysis. A microarray containing 3500 cDNA clones was first screened to enrich for genes affected by wounding in the immediate vicinity of the wound (4 h post wounding). 359 non-redundant putative wound responsive genes were then spotted on a smaller wound-response array for detailed analysis of spatial expression (local, adjacent and systemic), timing of expression (0.5, 4, 8, 17 h), and effect of hormone treatments (methyl jasmonate, ethylene and abscisic acid). Our results show that genes that respond early at the site of the wound also respond throughout the plant, with similar kinetics. Early-induced genes which respond systemically encode predominantly signal transduction and regulatory factors (36%), and the expression of many of them is also controlled by methyl jasmonate (about 35% of the 36%). Genes specific to the wound site and the wounded leaf have a slower response to wounding and are mainly metabolic genes. At the wound, many genes of the lignin biosynthesis pathway were induced. In silico analysis of the 5' promoter regions of genes affected by wounding revealed G-box-related motifs in a significant proportion of the promoters. These results show that the establishment of a systemic response to wounding is a priority for the plant, and that the local response at the wound site is established later. Ethylene and abscisic acid are involved in the local response, regulating repression of photosynthetic genes and expression of drought responsive genes respectively.

Abscisic Acid↗
PubMed1999

Localization-delocalization transition in quantum dots

Single-electron capacitance spectroscopy precisely measures the energies required to add individual electrons to a quantum dot. The spatial extent of electronic wave functions is probed by investigating the dependence of these energies on changes in the dot confining potential. For low electron densities, electrons occupy distinct spatial sites localized within the dot. At higher densities, the electrons become delocalized, and all wave functions are spread over the full dot area. Near the delocalization transition, the last remaining localized states exist at the perimeter of the dot. Unexpectedly, these electrons appear to bind with electrons in the dot center.

Journal Article↗
PubMed1993

[Analysis of the composition and spatial disposition of atherosclerotic plaques localized in epicardial coronary artery bifurcations in adults].

PURPOSE: To analyze macro and microscopic features of atherosclerotic plaques located in bifurcation of coronary arteries, defining their spatial disposition in those sites. METHODS: We studied 38 bifurcations of coronary arteries of patients whose cause of death was related to coronary artery disease. Histologic sections of 0.5mm were sequentially made from the main artery to the secondary branches. They were stained with hematoxilin-eosin technique. Histological analysis evaluated: a) morphologic composition of the plaques, b) degree of obstruction and c) plaque's disposition. RESULTS: a) Plaque's composition: fibrolipid plaques constituted 80% of the cases and mingled focal atrophy of the media at the base of the plaque in 61% with spots of total destruction and rupture of the elastic layers in 30%; b) degree of obstruction: ranged from 20% to 95%, with average 60 +/- 28%; c) disposition of plaques: we verified morphologic variation along the plaque, most of them (71%) being eccentric at bifurcation and not reaching the beginning of flow divider walls. CONCLUSION: Atherosclerotic plaques located in bifurcation of coronary arteries of adults are often fibrolipid plaques, eccentric, and their spatial disposition on those sites spare the beginning of the inner walls, reaching the outer walls.

Adult↗
PubMed2005

The role of large-scale spatially explicit and small-scale localized processes on the population dynamics of cereal aphids.

A field-scale study of the spatially explicit interaction between the carabid Poecilus cupreus Linnaeus, and two common aphid species (Sitobion avenae (Fabricius) and Metopolophium dirhodum (Walker)) in winter wheat was conducted. All three species showed considerable spatial pattern at the field scale. Activity-density of P. cupreus was an order of magnitude higher in the central part of the field compared to its periphery. Where P. cupreus activity-density was highest, S. avenae and M. dirhodum population peaks were delayed. Additionally, in the case of M. dirhodum, lower maximum counts were evident where P. cupreus activity-density was highest. An analysis of the movement of individual P. cupreus using release-recapture indicated that those beetles within the centre of the field exhibited reduced displacement, which may have caused the generation or maintenance of spatial pattern. Crop density was also measured throughout the field. Although crop density had no large-scale spatial pattern, its variability at the small-scale was consistent with an influence on aphid population dynamics. This study demonstrates empirically that both large-scale spatially explicit and small-scale localized processes influenced aphid population dynamics simultaneously.

Animals↗
PubMed2004

Spatial and temporal structure of edge-localized modes.

This Letter provides information on the spatial and temporal structure of periodic eruptions observed in magnetically confined laboratory fusion plasmas, called edge-localized modes (ELMs), and highlights similarities with solar eruptions. Taken together, the observations presented in this Letter provide strong evidence for ELMs being associated with a filamentlike structure. These filaments are extended along a field line, are generated on a 100 micros time scale, erupt from the outboard side, and connect back into the plasma. Such structures are predicted by a theoretical model based on the "ballooning" instability, developed for both solar and tokamak applications.

Journal Article↗
PubMed2003

Localization of human somatosensory cortex using spatially filtered magnetoencephalography.

A spatial filter algorithm based on minimum-variance beamforming (synthetic aperture magnetometry (SAM)) was applied to single trial neuromagnetic recordings in order to localize primary somatosensory cortex. Magnetoencephalography (MEG) responses to electrical stimulation of the right and left median nerve were recorded using a whole-head MEG system and localized using both SAM spatial filtering and dipole analysis. Spatial filtering was applied to single trial neuromagnetic recordings to produce 3-dimensional difference images of source power between active (0-50 ms) and control states (-50-0 ms) in the range of 15-300 Hz. Average difference between N20m dipole location and location of maximal increase in power in the SAM images was 3.7 mm (1.5 mm SD) and localized to primary somatosensory cortex. Time-frequency analysis of spatially filtered output for the peak SAM locations showed a brief (10 ms) increase in the 60-100 Hz band coincident with the N20m response and a longer duration (approx. 80 ms) increase in power in the 10-40 Hz band following N20m onset. These results indicate that beamformer based spatial filter methods such as SAM can be used to localize temporally discrete cortical activity produced by median nerve stimulation.

Adult↗
PubMed2006

Invasive advance of an advantageous mutation: nucleation theory.

For sedentary organisms with localized reproduction, spatially clustered growth drives the invasive advance of a favorable mutation. We model competition between two alleles where recurrent mutation introduces a genotype with a rate of local propagation exceeding the resident's rate. We capture ecologically important properties of the rare invader's stochastic dynamics by assuming discrete individuals and local neighborhood interactions. To understand how individual-level processes may govern population patterns, we invoke the physical theory for nucleation of spatial systems. Nucleation theory discriminates between single-cluster and multi-cluster dynamics. A sufficiently low mutation rate, or a sufficiently small environment, generates single-cluster dynamics, an inherently stochastic process; a favorable mutation advances only if the invader cluster reaches a critical radius. For this mode of invasion, we identify the probability distribution of waiting times until the favored allele advances to competitive dominance, and we ask how the critical cluster size varies as propagation or mortality rates vary. Increasing the mutation rate or system size generates multi-cluster invasion, where spatial averaging produces nearly deterministic global dynamics. For this process, an analytical approximation from nucleation theory, called Avrami's Law, describes the time-dependent behavior of the genotype densities with remarkable accuracy.

Cluster Analysis↗
PubMed2006

Complement factor H: spatial and temporal expression and localization in the eye.

PURPOSE: Complement factor H (CFH) is a component of the mammalian complement system, which regulates the alternative pathway of complement activation and protects the host cell from inappropriate complement activation. CFH is a key regulator of innate immunity, and CFH deficiency leads to membranoproliferative glomerulonephritis type II. A variation in human CFH, Y402H, has been shown to be associated with an increased risk for age-related macular degeneration. The authors describe studies on the spatial and temporal expression of the CFH gene and localization of this protein in ocular tissues to gain insight into its role in the eye. METHODS: CFH expression in human and mouse tissues was studied by quantitative RT-PCR and Western blot analysis, and localization of CFH was studied by immunohistochemical analysis followed by fluorescence microscopy. RESULTS: In human and mouse, CFH expression was found to be similar to the highest level of expression in the liver. In ocular tissue, CFH was detected in the distalmost optic nerve (3 mm) cut from the scleral surface of the eyeball, sclera, RPE-choroid, retina, lens, and ciliary body. In mouse, Cfh expression was observed from early embryonic stages, and in the eye its expression increased with age. CONCLUSIONS: A significant level of CFH expression is maintained in different ocular tissues during development and aging. Sustained high levels of CFH expression in eye tissues suggest that this protein may play a role in protecting these tissues from indiscriminate complement activation and inflammatory insult.

Aged↗
PubMed2005

Genetic drift within a protected polymorphism: enigmatic variation in color-morph frequencies in the candy-stripe spider, Enoplognatha ovata.

The candy-stripe spider, Enoplognatha ovata, exhibits a striking color polymorphism comprising three morphs. A number of lines of evidence strongly suggest that this polymorphism is maintained by natural selection: its presence in a sister species, E. latimana; the physical nature of the variation; the virtual lack of monomorphic populations; the highly consistent rank-order of morphs within populations; and the presence of large-scale clines associated with climatic variables. However, the absence of selection is equally strongly suggested by very local surveys of morph frequencies over space and time, perturbation experiments, and a variance in morph frequency between populations that is virtually independent of spatial scale. In addition, local spatial patterns in one study site (Nidderdale, Yorkshire, England) have been explained in terms of intermittent drift over half a century ago, a hypothesis supported here by the distributions of four other genetic markers (two allozyme and two visible polymorphisms). A heuristic model is suggested that reconciles these apparently contradictory messages regarding the importance of drift and selection in this system. It is proposed that when allele frequencies of the color morph redimita lie between approximately 0.05 and 0.3, the deltaq on q plot is very shallow, so that within this region, where the majority of populations lie, selection is weak and drift is the major force determining local morph frequencies. However, outside this range of frequencies, powerful selection acts to protect the polymorphism. This model may apply to polymorphisms in other species and explain why evidence of selection in natural populations is often elusive.

Animals↗
PubMed2000

Identification of the substrate of atrial vulnerability in patients with idiopathic atrial fibrillation.

BACKGROUND: Experimental studies have shown that atrial fibrillation (AF) causes remodeling, which facilitates AF perpetuation. AF may also, however, occur in patients without remodeling and underlying structural cardiac disease. The substrate for enhanced vulnerability in these patients is unknown. METHODS AND RESULTS: We studied 43 patients without structural heart disease: 18 patients with documented sporadic paroxysmal AF and 25 control patients without AF. In each patient, a decapolar catheter was positioned against the right atrial free wall, and a quadripolar catheter was positioned in the right atrial appendage. Unipolar electrograms were recorded. Atrial vulnerability was assessed according to an increasingly aggressive stimulation protocol. Mean local fibrillatory interval (FI) was used as an index of local refractoriness. Spatial dispersion of refractoriness was assessed through the calculation of the coefficient of dispersion (CD), which was defined as the SD of mean local FI expressed as a percentage of the mean FI. In the AF group, AF was induced with a single extrastimulus in 16 of 18 patients; the CD was 5.4+/-2.6, and the mean FI was 164+/-29 ms. In the control group, AF could be induced only with more aggressive pacing in 23 of the 25 patients; the CD was 1.4+/-0.7 (P<0.0001), and the mean FI was 175+/-26 ms (NS). CONCLUSIONS: Patients with idiopathic AF showed increased dispersion of refractoriness, which may be the substrate for the observed enhanced inducibility and spontaneous occurrence of AF.

Adult↗
PubMed1998

Detection of object orientation and spatial changes by mice: importance of local views.

This study examines the types of information used by mice to detect changes in their environment. After a period of habituation to an open field containing three bicolored cube-shaped objects, we modified the spatial configuration of the objects or rotated the objects 180 degrees, or both. We noted that whatever the modification, mice reexplored the objects. This shows that mice are able to detect both topological changes and, in particular, changes in the orientation of objects. This is possible only if mice can establish a local view of the objects in relation to a stable element of their environment. A second experiment showed that this stable element is in fact a pattern within the open field and not an element of the distal environment. These two experiments demonstrate the importance of local views in spatial representation for rodents.

Animals↗
PubMed1992

Neural derivation of sound source location: resolution of spatial ambiguities in binaural cues.

Cues for sound localization are inherently spatially ambiguous. Nevertheless, most neurons in the barn owl's optic tectum (superior colliculus) have receptive fields for broadband noise stimuli that are restricted to a single region of space. This study characterizes the spatial ambiguities associated with two important sets of localization cues, interaural level differences (ILDs) and interaural phase differences (IPDs), and describes how information is integrated within and across frequencies to resolve these ambiguities. The auditory receptive fields of neurons in the optic tectum were measured with free-field sounds presented from a movable loudspeaker. In contrast to the single regions typical for broadband receptive fields, receptive fields for tonal stimuli usually included additional discrete regions of space (accessory fields). Based on acoustic measurements of ILD and IPD cues made in the external ear canals, it was shown that accessory fields corresponded to locations from which sound sources produced ILD and IPD values that were approximately the same as those arising from the broadband receptive field. In addition, accessory fields had inhibitory surrounds, corresponding to locations from which sound sources produced substantially different combinations of ILD and IPD values. Where an accessory field for one frequency overlapped with the inhibitory surround of a second frequency, an excitatory response to the first frequency could be reduced or eliminated by addition of the second frequency. Because tonal receptive fields for different frequencies always overlapped in the region of the broadband receptive field but tended not to overlap elsewhere, this integration of excitation and inhibition can account for the restriction of broadband receptive fields to a single region of space.

Animals↗
PubMedDate not supplied

[Stereotaxic microsurgical resection of intracranial tumors guided by imaging and assisted by computer].

INTRODUCTION: The microsurgical techniques for resection of intracranial lesions are limited where anatomical references do not exist or cannot be used as guides in the dissection of deeply located lesions or in more superficial eloquent areas. The stereotaxic guide, guided by imaging gives precise volumetric and geometric definition in intracranial lesions. Its application in the resection of intracranial tumors has special characteristics due to their biological condition and varied localization. OBJECTIVES: Spatial orientation during surgery is essential. We show this application of stereotaxic surgery in the Centro Internacional de Restauración Neurológica (CIREN) in La Havana, Cuba, between May 1994 and February 1988, describing 65 microsurgical operations done using stereotaxis in 62 patients with intracranial cerebral tumors. PATIENTS AND METHODS: The procedure was divided into three stages: acquiring an image, computerized axial tomography and surgical planning, with the STASSIS planning system and microsurgical procedures, including systems of stereotaxis: Leksell, Micromar and Estereoflex. RESULTS: Of the total, 27 of these patients had glial tumors, 33 non-glial tumors and only 2 had non-neoplastic lesions of different sites and sizes. A total of 30 resections were done. Surgical morbidity was minimal and there was no surgical mortality. CONCLUSIONS: The main advantages of this method are: exact localization of the site for craniotomy, easy spatial orientation and ease in distinguishing the delimitation between the tumour and the healthy tissue. It has been shown that Estereoflex may be used in cerebral microsurgery.

Adolescent↗
PubMed2000

Non-destructive determination of local strain with 100-nanometre spatial resolution

Structure sizes of approximately 180 nm are now standard in microelectronics, and state-of-the-art fabrication techniques can reduce these to just a few tens of nanometres. But at these length scales, the strain induced at interfaces can locally distort the crystal lattice, which may in turn affect device performance in an unpredictable way. A means of non-destructively characterizing such strain fields with high spatial resolution and sensitivity is therefore highly desirable. One approach is to use Raman spectroscopy, but this is limited by the intrinsic approximately 0.5-microm resolution limit of visible light probes. Techniques based on electron-beam diffraction can achieve the desired nanometre-scale resolution. But either they require complex sample preparation procedures (which may alter the original strain field) or they are sensitive to distortional (but not dilational) strain within only the top few tens of nanometres of the sample surface. X-rays, on the other hand, have a much greater penetration depth, but have not hitherto achieved strain analysis with sub-micrometre resolution. Here we describe a magnifying diffraction imaging procedure for X-rays which achieves a spatial resolution of 100nm in one dimension and a sensitivity of 10(-4) for relative lattice variations. We demonstrate the suitability of this procedure for strain analysis by measuring the strain depth profiles beneath oxidized lines on silicon crystals.

Journal Article↗
PubMed2000

Creases as local features of deformation grids.

To help identify underlying developmental or pathological processes, biological shape differences often are represented as diffeomorphisms of a Cartesian coordinate grid. The problem addressed here is the extraction of spatially discrete, localized, organized features of such transformation grids. Some features can be identified with variants of the singularity (x, y) --> (x, x2y + y) that are visually evident as creases in suitably enhanced grid diagrams. The crease is a non-generic singularity at which a pair of cusps appears as a function of a parameter for extrapolation. The examples here show how these representations extract statistically informative and scientifically helpful features from deformations that help characterize two brain diseases, schizophrenia and Fetal Alcohol Syndrome, in two dimensions. Under smoothing by relaxation of bending energy against Euclidean distance, one analogue to multiscale analysis for discrete punctate data, creases are robust in location and orientation.

Brain↗
PubMed1983

Sound localization in subjects with impaired hearing. Spatial-discrimination and interaural-discrimination tests.

In order to get a systematic picture of how various hearing impairments and neurologic disorders may affect sound localization, psychophysical spatial- and lateralization-discrimination measurements were performed on 140 subjects, including 69 with different types of hearing impairments, 32 with neurological diseases, and 39 with normal hearing. The quantities measured were: in the freefield, the horizontal minimum audible angle (MAA) at eight reference azimuths around the head and the vertical MAA straight ahead; with headphones, the just-noticeable difference (JND) in interaural time delay and the JND in interaural intensity difference. The standard stimulus was broadband (0.25-10 kHz), pulsed (1-sec), noise presented at a suprathreshold level for both ears (65-100 dB SPL). The results show that there exist characteristic impairments of sound localization in the different types of hearing impairments tested. On a general level, the results are consistent with the concept that the localization of sound relies on a decision made by the central auditory system based on a number of cues present in the acoustic signal at the two ears. The cues tested in our study are: 1) the interaural time difference, 2) the interaural intensity difference, and 3) the spectrum of the received signal at each ear. At a more specific level, the sound localization impairments found in conductive hearing losses are interpreted as bone-conduction effects, the results found in sensorineural hearing losses are interpreted as consequences of impaired or preserved spectral processing, the results in neurinomas are interpreted as impaired signal transmission in the auditory nerves, and the results of subjects with central involvements suggest that separate processors exist at some level in the central auditory system for the different localization cues. Finally, comments are made about the practical clinical significance of sound localization tests in the audiological and neurological evaluation of patients.

Adolescent↗
PubMed1992

Confidence limits for the parameter estimation in the dipole localization method on the basis of spatial correlation of background EEG.

A new residual function in the inverse problem of equivalent dipole localization methods is proposed which is based on the spatial correlation of the background EEG. This residual has the advantage that it allows the calculation of confidence limits for dipole model parameters. The method was applied to VEP data, and it was studied how the localization precision depends on the recording time of the EEG. It was found that the tangential position of an equivalent dipole can be located at 99% confidence in a region of the order 7 x 7mm for a head radius of 10cm, while the 99% confidence interval of the depth estimate is approximately 1cm, with a recording time of 20 minutes. It was also observed that an EEG recording time of more than 10-15 minutes is needed to obtain stable localization precision estimates.

Brain↗
PubMed2005

Spatial and temporal predictability of the parasite community structure of a benthic marine fish along its distributional range.

The search for consistent patterns of organisation in parasite communities remains a central theme in parasite community ecology. However, to date, much evidence comes from studies without replication in both space and time; when replicate communities are examined, repeatable patterns are rarely observed. Here we determine, using nested subset analyses, whether the infracommunities of ectoparasites and endoparasites of a benthic marine fish (Sebastes capensis) show non-random structure. Then we examine the spatial repeatability of parasite community structure across the host's distribution in the southern Pacific, and the temporal repeatability of ectoparasite community structure from one locality. In total, 537 fish were captured from different latitudes (between 11 degrees S and 52 degrees S) along the Pacific coast of South America; a further 122 specimens were captured in two other years from one of the sampling localities, Valdivia (40 degrees S). In spite of variation in fish sizes among samples, fish size generally did not correlate with either ecto- or endoparasite species richness. The ecto- and endoparasite species richness of the component communities were also not correlated with fish sample size across the nine localities. Significant nested patterns were found in the ectoparasite communities of S. capensis at all eight localities, except at latitude 52 degrees S. Significant nested patterns were also found in the endoparasite infracommunities of S. capensis at seven of the nine localities, the exceptions being those from latitudes 11 degrees S and 20 degrees S. On a temporal scale, significant nestedness was observed in the ectoparasite infracommunities of S. capensis during each of the 3 years of sampling at Valdivia. In general, the same parasite species are responsible for the repeatability of nested patterns, though their importance varies among localities. The spatial and temporal predictability of the parasite community structure in S. capensis may be associated with the fish's benthic habitat and territorial behavior, suggesting that host biology may be a key determinant of the structure of parasite communities.

Animals↗