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At least 379 records · Page 21Linked to original sources
PubMed1998

Localization of spatial attention processes with the aid of a probe technique.

A sudden visual onset is thought to 'attract attention to its location' within less than 100 ms. We attempted to measure the effect of this attentional process on the event-related potential (ERP) to a probe presented about 140 ms after the onset, and to delineate the spatiotemporal characteristics of such an effect, if any. ERPs were recorded from 30 channels from 6 subjects while they performed a target detection task. Both targets and probes could be located in each of the 4 quadrants (eccentricities 6.1 degrees and 7 degrees, respectively). For a given single target, the subsequent probe was either presented near the location of the target ('valid target') or at the diagonal opposite ('invalid target'). Appropriate 'neutral' conditions (probes preceded by no target, or by simultaneous targets in all quadrants) were applied, and ERPs to probes were corrected for the contribution of the ERPs to targets. The earliest effect of (in)validity was found at about 120 ms after probe onset for lower field probes. This effect consisted of enhanced posterior positivity for valid relative to neutral relative to invalid conditions. This positivity was superposed on a contralateral, extrastriate negative ongoing wave peaking at about 150 ms ('N150'). Source localization suggested that the (in)validity effects originate from deep medial parietal areas. The source corresponding to the N150 activity was not influenced by (in)validity. An earlier deflection to the probe at 80 ms ('NP80') depended on location, but not on (in)validity, and seemed to be of striate origin. Results are discussed in terms of a model postulating an attention-independent 'input module' from which activation is fed to a 'location module' embodying the actual attention mechanism.

Adult↗
PubMed1988

Integrated MR imaging and spectroscopy with chemical shift imaging of P-31 at 1.5 T: initial clinical experience.

A section-selective three-dimensional phosphorus-31 chemical shift imaging (CSI) experiment was evaluated as the spatial localization method for spectroscopy in an integrated clinical magnetic resonance (MR) imaging and spectroscopy examination. The results of a CSI experiment can be displayed as either spectra related to specific voxels or "metabolite maps," in which the relative concentration of a given metabolite is displayed as an overlay of the MR image. This method was applied to the study of a soft-tissue mass and to a meningioma. The total imaging time in each case was 17 minutes with a voxel size of 27 cm3 in the extremity and 64 cm3 in the brain. The total time to set up this part of the study was about 10 minutes. No additional shimming was necessary when the center of the field of view selected for the CSI experiment was located at or near isocenter. The promising results obtained with this approach make the CSI method an attractive choice of spatial localization method.

Adult↗
PubMed1998

Human breast lesions: characterization with proton MR spectroscopy.

PURPOSE: To assess the clinical usefulness of spatially localized hydrogen-1 magnetic resonance (MR) spectroscopy in distinguishing benign from malignant lesions on the basis of total choline levels. MATERIALS AND METHODS: These studies were performed at 1.5 T with a four-channel multicoil that compresses the breast sagittally. Contrast material-enhanced MR imaging and single-voxel H-1 MR spectroscopy were performed in 17 patients (age range, 25-68 years) who had nonspecific mammographic findings. Histopathologic correlations were made from biopsy or surgical specimens. Ten patients had various malignant breast lesions 1-4 cm in diameter, and seven patients had benign processes. RESULTS: Most studies were performed with nominal voxel sizes (< 2 cm3). Spectra obtained with an echo time of 31 msec showed resonances from water and mobile fatty acids and, in some cases, the N-trimethyl resonance of choline-containing compounds (Cho) at 3.2 ppm. The absolute concentration of Cho in each lesion was determined with a phantom containing 1 mmol/L Cho as an external reference. On the basis of reference measurements, the least detectable level of Cho was 0.2 mmol/L. With this threshold, seven of 10 malignant lesions showed detectable levels of Cho. In contrast, Cho was seen in only one patient with an extremely rare benign process, a tubular adenoma. The remaining six patients with benign processes demonstrated no detectable Cho levels. CONCLUSION: Spatially localized H-1 MR spectroscopy can provide sufficient sensitivity and spectral resolution at 1.5 T to demonstrate Cho in human breast lesions with a spectroscopic protocol that provides up to 1-cm3 resolution. Determining the presence of Cho may provide a useful test for malignancy.

Adult↗
PubMed1996

RT-PCR-based method to localize the spatial expression of genes in the mouse blastocyst.

We report an RT-PCR-based assay to analyze the spatial pattern of expression of genes in mouse blastocysts. The assay is based on comparing the amount of an amplicon for a specific gene in isolated inner cell mass cells to that in intact blastocysts and using this ratio to calculate the relative amount of transcript per inner cell mass cell or trophectoderm cell. Validation of the assay is demonstrated by documenting that the level of fgf-4 transcripts in inner cell mass cells is approximately 13 times greater than that in trophectoderm cells, and that the level of endo A transcripts in trophectoderm cells is approximately 18 times greater than that in inner cell mass cells; results of others have shown that fgf-4 and endo A expression are enhanced in the inner cell mass cells and trophectoderm cells, respectively. Using this assay, we find that transcripts for both the EGF receptor and TGF-alpha are present in both the inner cell mass and trophectoderm cells and that on a per cell basis, essentially equal amounts of each transcript are present in these two cell types. We also demonstrate by laser-scanning confocal microscopy that TGF-alpha protein is uniformly present in all cells of the blastocyst.

Animals↗
PubMed1987

Immunocytochemical localization and spatial relation to the adenohypophysis of a somatostatin-like and a corticotropin-releasing factor-like peptide in the brain of four amphibian species.

The distribution of somatostatin (SRIF) - and corticotropin-releasing factor (CRF)-like - immunoreactive material was studied in the brain of four amphibian species (Ambystoma mexicanum, Pleurodeles waltlii, Xenopus laevis, Rana ridibunda) by use of immunocytochemistry. A wide network of SRIF-immunoreactive fibers and numerous perikarya were observed in all amphibians examined, with a dense accumulation of nerve endings in the external layer of the median eminence (ELME). In the representatives of the four amphibian species the CRF-like system was more circumscribed. Immunoreactive perikarya were present in the preoptic area, mainly in a ventrobasal position, and in the interpeduncular nucleus. The tract running along the ventral part of the tuber cinereum ends in the ELME facing the rostroventral lobe of the pars distalis that contains corticotrophs. CRF fibers were scarce or absent in the neural lobe. In all species studied in the present work, CRF fibers end in the area of the ELME close to the pituitary lobe containing corticotrophs. This correlation is similar to that reported for the Japanese quail and several teleosts.

Ambystoma↗
PubMed2006

Regulated and polarized PtdIns(3,4,5)P3 accumulation is essential for apical membrane morphogenesis in photoreceptor epithelial cells.

BACKGROUND: In a specialized epithelial cell such as the Drosophila photoreceptor, a conserved set of proteins is essential for the establishment of polarity, its maintenance, or both--in Drosophila, these proteins include the apical factors Bazooka, D-atypical protein kinase C, and D-Par6 together with D-Ecadherin. However, little is known about the mechanisms by which such apical factors might regulate the differentiation of the apical membrane into functional domains such as an apical-most stack of microvilli or more lateral sub-apical membrane. RESULTS: We show that in photoreceptors Bazooka (D-Par3) recruits the tumor suppressor lipid phosphatase PTEN to developing cell-cell junctions (Zonula Adherens, za). za-localized PTEN controls the spatially restricted accumulation of optimum levels of the lipid PtdIns(3,4,5)P3 within the apical membrane domain. This in turn finely tunes activation of Akt1, a process essential for proper morphogenesis of the light-gathering organelle, consisting of a stack of F-actin rich microvilli within the apical membrane. CONCLUSIONS: Spatially localized PtdIns(3,4,5)P3 mediates directional sensing during neutrophil and Dictyostelium chemotaxis. We conclude that a conserved mechanism also operates during photoreceptor epithelial cell morphogenesis in order to achieve normal differentiation of the apical membrane.

Adherens Junctions↗
PubMed1999

Spatially constrained localized transport regions due to skin electroporation.

Rapid, controlled molecular transport across human skin is of great interest for transdermal drug delivery and minimally invasive chemical sensing. Short, high-voltage pulses have been shown previously to create localized transport regions in the skin. Here, we show that these regions can be constrained to occur at specific sites using electrically insulating masks that restrict the field lines. The increase in total ionic and molecular transport per area was comparable to the levels observed in unconstrained electroporation of human skin. Constraining the area of intervention to encompass small areas of interest, a primary feature in the design of microdevices for transdermal drug delivery, can provide the same levels of flux as the unconstrained case.

Biological Transport↗
PubMed2001

Characterization of patterned irregularity in locally interacting, spatially extended systems: Ventricular fibrillation.

The re-entrant ventricular arrhythmias of monomorphic ventricular tachycardia and fibrillation are produced by abnormal spatio-temporal patterns of propagation in the ventricular myocardium. These behaviors can be described by solutions of reaction-diffusion equation excitable medium models. The direct comparison of such solutions with existing experimental observations is virtually impossible as there are too many factors to be taken into account, including not only the complicated dynamics of the re-entrant waves of excitation in the tissue, but also the way the appearance of these waves on the surface is modified by the inhomogeneity, anisotropy and three-dimensional nature of heart tissue. One way of indirect comparison is to compare characteristics of the complexity of the model and the real data, that are invariant under these modifications of the signal. Karhunen-Loeve decomposition is a standard tool for evaluating the complexity of multidimensional signals. A comparison of the separate and conjoint complexities of the signals on the opposite sides of the preparation can be considered as an indicator how much three-dimensional effects are essential in the preparation behavior. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed1994

Localizing the spatial and temporal electromagnetic fields on the axis of a lossy cylinder.

Given a specified form, both in time and space, for the electromagnetic fields on the axis of a lossy cylinder, we determine, analytically, the required azimuthally symmetric source distribution on the surface of the cylinder that generates such internal fields. We then show that this source is equivalent to an array with finite number of cylindrical slots in a metal encasing that are impulsed by specified voltages at a finite sequence of discrete times. A confirming forward calculation exhibits excellent agreement between the specified field form and that generated by the array of cylindrical slots. Potential applications are to hyperthermic cancer therapy, bioelectromagnetics and nondestructive testing.

Electromagnetic Fields↗
PubMed2005

A phenomenological theory of spatially structured local synaptic connectivity.

The structure of local synaptic circuits is the key to understanding cortical function and how neuronal functional modules such as cortical columns are formed. The central problem in deciphering cortical microcircuits is the quantification of synaptic connectivity between neuron pairs. I present a theoretical model that accounts for the axon and dendrite morphologies of pre- and postsynaptic cells and provides the average number of synaptic contacts formed between them as a function of their relative locations in three-dimensional space. An important aspect of the current approach is the representation of a complex structure of an axonal/dendritic arbor as a superposition of basic structures-synaptic clouds. Each cloud has three structural parameters that can be directly estimated from two-dimensional drawings of the underlying arbor. Using empirical data available in literature, I applied this theory to three morphologically different types of cell pairs. I found that, within a wide range of cell separations, the theory is in very good agreement with empirical data on (i) axonal-dendritic contacts of pyramidal cells and (ii) somatic synapses formed by the axons of inhibitory interneurons. Since for many types of neurons plane arborization drawings are available from literature, this theory can provide a practical means for quantitatively deriving local synaptic circuits based on the actual observed densities of specific types of neurons and their morphologies. It can also have significant implications for computational models of cortical networks by making it possible to wire up simulated neural networks in a realistic fashion.

Journal Article↗
PubMed1992

[Effect of various light sources on visual functions in the age aspect. I. Conscious reaction time and the manual spatial visual localization].

The authors present the results of investigations performed in 28 right-handed, normally seeing persons divided into 2 groups: 15 of them were in productive age and 13 in older age. The authors compared the dynamics of the behaviour of the visual functions in dependence on the age of the subjects and the stay in the glow and sodium light. No adverse influence of the sodium light on the hand localization could be detected, instead it seems that it negatively influenced the selective reaction in older productive persons in the sense of an increased number of faults.

Adult↗
PubMed1997

Spatial analysis of the distribution of LaCrosse encephalitis in Illinois, using a geographic information system and local and global spatial statistics.

The spatial and temporal distribution of LaCrosse encephalitis cases in Illinois was analyzed using a geographic information system (GIS) and spatial statistics. Case data were obtained from the Illinois Department of Public Health and mapped on the county, town, and address level. Human cases were concentrated in and around the city of Peoria in central Illinois. Local spatial statistics were used to identify hot spots where cases appear to be concentrated in the Peoria region. Several small towns surrounding the city of Peoria appeared as foci where cases were most common. Second-order spatial analysis of the case distribution was conducted on the address level. Cases were clustered within a range of 3.0 km in the city of Peoria. Since most cases appear to be associated with residential (peridomestic) exposure, and since several cases have been reported from neighboring addresses, transmission may be concentrated around specific sites (hardwood ravines, tire piles). The GIS and spatial analysis may be useful in identifying and targeting for intervention potential sites of enzootic transmission.

Adolescent↗
PubMed1977

Spatial frequency and light-spread descriptions of visual acuity and hyperacuity.

Resolution (visual acuity) and differential spatial localization (hyperacuity) targets were selected to allow rigorous psychophysical measurements as well as ready expression of both their spatial frequency spectrum and their retinal image light distribution. Thresholds were about 1 arc min for acuity and 4-6 arc sec for hyperacuity. As is consistent with the reciprocal relationship between the space and spatial frequency domains, the small locally restricted spatial differences between just distinguishable patterns are represented in the frequency domain by equally small differences, which are distributed over the entire spatial frequency spectrum. While they occur in many test situations, phase variations of spatial frequency components are not necessary for achieving optimum acuity and hyperacuity.

Female↗