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Results for “spatial localization”

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At least 127 records · Page 7Linked to original sources
PubMed1991

The effects of superior colliculus lesions in hamsters: feature detection versus spatial localization.

This study was aimed at further documenting the effects of collicular lesions in exploratory activity in the hamster. Following habituation to a set of four objects placed in an open field, collicular and sham-operated hamsters were confronted to a change in the initial situation in which one object was replaced by a new one in a familiar location or in a new location, or a familiar object was moved to a new location, or was left in the same location (control condition). Hamsters sustaining lesions of the superior colliculus and sham-operated hamsters were found to habituate at the same rate. The surgical treatment modified the reactions to the spatial change. Intact hamsters reacted selectively to the new object, whatever its location. In contrast, collicular animals did not react to the familiar object when it was in a new location. Nevertheless, they were able to detect the new object when it replaced a familiar object at the same location. However, when the new object was at a new location, there was only a tendency in collicular hamsters to react to this change. When no change was made in the initial situation, no change in exploratory activity was observed in either group. These results, together with others, suggest that the rodent's superior colliculus is not directly involved in object discrimination, but plays a crucial role in the attentional components of spatial behavior.

Animals↗
PubMedDate not supplied

Improvement of precision in spatial localization of radio-opaque markers using the two-film technique.

Radio-opaque markers implanted inside or placed on the skin of patients can be used to detect set-up errors and patient motion. The effects of imaging geometry accuracy for standard radiotherapy equipment on the precision of calculating the positions of radio-opaque spherical markers using two orthogonal radiographic film projections is investigated. Inaccuracies in the imaging geometry are computed from the manually digitized positions of the marker images on each film pair. Actual marker locations are calculated with a precision limited only by the variance in manual digitization by incorporating those imaging geometry inaccuracies into their computation. Results of a phantom study using a grid of markers in a plastic block indicate that submillimeter precision can be obtained for the spatial coordinates of individual markers, and that the precision is not sensitive to the small inaccuracies in imaging geometry present within the mechanical tolerances of modern radiotherapy treatment machines and simulators.

Humans↗
PubMed1986

Spatial localization in infancy: position constancy in a square and circular room with and without a landmark.

The ability of 8-month-old infants to localize an event from a new direction of facing was tested in a square and a circular room with and without a landmark. Subjects were trained to anticipate the site from 2 directions of facing and then tested in a new direction of facing. The number of trials to a criterion of learning, the number of subjects looking first at the event site after reorientation, and the time spent in doing so were recorded. Taken together, the results show that at 8 months ability to identify the site of an event after reorientation is based on the spatial relationship between the event and environmental features. The latter include features associated with room shape as well as a landmark at the site of the event.

Attention↗
PubMed1988

Promoter determining the timing and spatial localization of transcription of a cloned Streptomyces coelicolor gene encoding a spore-associated polypeptide.

Streptomyces coelicolor is a filamentous, gram-positive bacterium that exhibits a complex cycle of morphological differentiation involving the formation of an aerial mycelium of multinucleoid hyphae which undergo septation to form long chains of spores. We report the identification of two proteins of 13 and 3 kilodaltons, designated SapA and SapB, respectively, that are produced during formation of the aerial mycelium and are found in assocation with purified, mature spores. We cloned the structural gene (sapA) for one of these spore-associated proteins. Nucleotide sequence analysis suggests that the 13-kilodalton polypeptide is derived from a larger pre- or preproprotein containing a leader sequence of 37 amino acids. Nuclease protection-hybridization analysis and experiments using the Vibrio harveyi, luciferase-encoding luxAB operon as a gene tag demonstrated that expression of sapA is controlled from a promoter contained within a region of less than 110 base pairs in length, whose transcription start site is located approximately 50 base pairs upstream from the initiation codon for the sapA open reading frame. Transcription of sapA was induced at the time of appearance of the aerial mycelium, and the level of sapA transcripts was significantly reduced in certain mutants blocked in aerial mycelium (bld) and or spore (whi) formation. As further evidence of the association of sapA transcription with morphological differentiation, experiments in which we monitored sapA transcription topographically by use of a sapA-luxAB operon fusion demonstrated a close spatial correlation between colony regions undergoing aerial mycelium formation and zones of sapA-promoted light emission.

Amino Acid Sequence↗
PubMed1995

Visual-spatial localization by patients with frontal-lobe lesions invading or sparing area 46.

Monkeys with unilateral principal sulcus (PS) lesions show a contralateral deficit in localizing remembered targets, especially as the recall interval is lengthened. We tested 20 patients with unilateral frontal-lobe excisions that invaded (FI) or spared (FS) area 46 (putative homologue of PS) and 32 normal controls (NC) on a task where subjects had to indicate the location of a light dot either immediately, or after 30 s, with or without interference. The FI group was worse than the NC group following both delay conditions. NC and FS groups differed only after interference. We concluded that area 46 is involved in recalling the location of visual targets, but unlike the monkey, the deficit is not restricted to a particular part of the visual field.

Adult↗
PubMed1986

Abnormal spatial localization in patients with herpes zoster ophthalmicus. Evidence for the presence of proprioceptive information.

Patients with herpes zoster of the ophthalmic branch of the trigeminal nerve and normal ocular motility were examined. They were asked to point to targets without the sight of their own hand. Significant errors were found on the affected side. Proprioceptive information of the extraocular muscles is assumed to travel in the trigeminal nerve, and these results thus suggest the existence of peripheral afferent signals influencing eye-hand coordination.

Herpes Zoster Ophthalmicus↗
PubMedDate not supplied

A hypercapnia-based normalization method for improved spatial localization of human brain activation with fMRI.

An issue in blood oxygenation level dependent contrast-based functional MRI is the accurate interpretation of the activation-induced signal changes. Hemodynamic factors other than activation-induced changes in blood oxygenation are known to contribute to the signal change magnitudes and dynamics, and therefore need to be accounted for or removed. In this paper, a general method for removal of effects other than activation-induced blood oxygenation changes from fMRI brain activation maps by the use of hypercapnic stress normalization is introduced. First, the effects of resting blood volume distribution across voxels on activation-induced BOLD-based fMRI signal changes are shown to be significant. Second, the effects of hypercapnia and hypoxia on resting and activation-induced signal changes are demonstrated. These results suggest that global hemodynamic stresses may be useful for non-invasive mapping of blood volume. Third, the normalization technique is demonstrated.

Brain↗
PubMed1984

Depth pulse sequences for surface coils: spatial localization and T1 measurements.

The depth pulse sequences theta;[2 theta(+/- x, +/- y)]2 and 2 theta;theta(+/- x);[2 theta(+/- x, +/- y)]2 have been implemented with a 20 mm diameter two-turn surface coil operating at 31P resonance (89.96 MHz). In these sequences theta refers to the pi/2 rf pulse at the center of the sensitive region of the coil, +/- x and +/- y denote the four orthogonal phases of the rf pulses, and ";" represents an optional brief delay (e.g., 4 microseconds) between pulses to facilitate switching between different phases. Localization of the sensitive region was demonstrated with phantom samples by in vivo monitoring of rat livers and detection of necrotic regions of subcutaneously implanted tumors. The inversion-recovery pulse sequence, 2 theta-tau-theta(+/- x);[2 theta(+/- x, +/- y)]2, where tau is a variable delay, was employed to measure the spin-lattice relaxation time of a selected region, which could be varied by changing the pulse width and the size of the surface coil.

Animals↗
PubMed1985

SHARP NMR biomedical spatial localization.

An application of the Slepian-Pollak-Landau "time and band limited functions" is found in NMR imaging. The precise context is best described by the rotating-frame dynamics of the Bloch equations, where an analogy is made to the problem of simultaneously concentrating a function in time and frequency. The appropriately modulated rf fields are found to yield excellent response characteristics when used in numerical simulations of the Bloch equations.

Magnetic Resonance Spectroscopy↗
PubMed1990

A homonuclear shift correlated and spatially localized spectroscopy using stimulated echoes.

A new method which combines localized high-resolution proton NMR spectroscopy with two-dimensional correlated spectroscopy using stimulated echoes is presented. Stimulated-echo correlated spectroscopy (STECSY) is a straightforward extension of the STEAM method. Experiments with phantoms illustrate the efficacy of STECSY. An in situ application on rat adipose tissue demonstrates that STECSY is a helpful tool with which to select and assign resonances in complex 1H NMR spectra.

Adipose Tissue↗
PubMed1993

An assessment of spin-echo rotating-frame imaging for spatially localized determination of short T2 relaxation times in vivo.

The rotating frame of localized spectroscopy can be augmented by the inclusion of a refocusing pulse to enable the measurement of T2 relaxation times. This technique is particularly appropriate for determining short relaxation parameters due to the absence of time consuming switched B(omicron) field gradients. We have evaluated the accuracy of this protocol by measuring localized T2s in the range of 1 to 20 ms. Preliminary data obtained from muscle and liver of normal and iron overloaded human subjects are also presented.

Magnetic Resonance Imaging↗
PubMed1999

Stimulated anti-echo selection in spatially localized NMR spectroscopy.

Spectral localization using the stimulated-echo acquisition mode (STEAM) is one of the most popular methods in volume-localized in vivo NMR spectroscopy. The localized volume signal is generated via stimulated echoes from spins excited by three 90 degrees RF pulses, and the conventional STEAM sequence detects the stimulated-echo signal. From an analysis of the STEAM pulse sequence using the coherence transfer pathway formalism, stimulated anti-echoes are also formed by the same pulse sequence, which constitute the other half of the localized signal in the STEAM experiment. A new scheme of pulsed field gradients for the selection of stimulated anti-echoes was proposed, and localized spectroscopy in the stimulated anti-echo selection mode was achieved on a phantom and from in vivo rat brain.

Animals↗
PubMed2000

Comparative spatial localization of protein-A-tagged and authentic yeast nuclear pore complex proteins by immunogold electron microscopy.

The nuclear pore complex (NPC) mediates protein and RNP import in and RNA and RNP export out of the nucleus of eukaryotic cells. Due to its genetic tractability, yeast offers a versatile system for investigating the chemical composition and molecular architecture of the NPC. In this context, protein A tagging is a commonly used tool for characterizing and localizing yeast NPC proteins (nucleoporins). By preembedding anti-protein A immunogold electron microscopy (immunogold EM), we have localized two yeast nucleoporins, Nsp1p and Nic96p, in mutant yeast strains recombinantly expressing these nucleoporins tagged with four (Nsp1p) or two (Nic96p) IgG binding domains of protein A (i.e., ProtA-Nsp1p and ProtA-Nic96p). We have compared the location of the recombinant fusion proteins ProtA-Nsp1p and ProtA-Nic96p (i.e., as specified by their protein A tag) to the location of authentic Nsp1p and Nic96p (i.e., as defined by the epitopes recognized by corresponding nucleoporin antibodies) and found all of them to reside at the same three NPC sites. Hence, recombinant expression and protein A tagging of the nucleoporins Nsp1p and Nic96p have not caused any significant mislocation of the fusion proteins and thus enabled mapping of these two yeast nucleoporins at the ultrastructural level in a faithful manner.

Calcium-Binding Proteins↗
PubMed1994

The spatial localization of homologous chromosomes in human fibroblasts at mitosis.

Chromosomes from ten human male fibroblast metaphases were completely reconstructed from electron micrographs of serially sectioned material. Chromosome centromere positions were determined by finding the three-dimensional coordinates of the centromere midpoint. The data set showed the identity of nine chromosome types (chromosomes 1, 2, 3, 6, 9, 16, 17, 18 and the Y chromosome) preserved as they are positioned in vivo. The results indicate that there is (1) no significant association of the homologous chromosomes examined, (2) a significant tendency for a central location of the Y chromosome and of chromosome 18, (3) a significant tendency for a peripheral location of chromosome 6, (4) no significant tendency for homologous chromosomes to reorganize as metaphase advances and (5) no significant differential condensation across the metaphase plate. Therefore, the only organization pattern observed for the centromeres of the homologous chromosomes studied is some sorting by size across the metaphase plate. These results may be typical of dividing cell types. Different chromosome arrangements are found in some non-dividing cell types (e.g. mammalian brain cells). The different distributions of chromosomes in different cell types can be considered as forms of "nuclear differentiation". It is postulated that nuclear differentiation may be related to cell differentiation.

Cell Differentiation↗
PubMed1995

Spatial localization: tests of a two-process model.

The present study examined the recently proposed two-process model of localization performance in which a shift of attention, providing coarse location information, is followed by a saccadic eye movement, providing fine location information. In experiment 1 the nature of the localization response was manipulated. In contrast to the indirect response mode used in the study by Adam et al., i.e., manipulating the "arrow" keys to move the cursor to the target location, experiment 1 required subjects to point to the target location. The high degree of similarity between the pattern of results obtained with the pointing and cursor response indicated that performance in the localization paradigm was not differentially affected by the nature of the required response. In experiment 2 the characteristics of the backward masking stimulus was manipulated by employing three masking conditions: (1) a long-duration mask; (2) a short-duration mask (100 ms); and (3) a no-mask condition. Results showed that the long-duration mask caused interference at short and facilitation at long intervals between onset of target and mask; the short-duration mask caused interference only at short intervals. Overall the findings were consistent with the two-process model of localization performance.

Adult↗
PubMed1994

Temporal and spatial localization of type I and II collagens in human thyroid cartilage.

Thyroid cartilages of various ages were investigated by immunofluorescence staining for localization of the fibrillar collagen types I and II in order to understand the tissue remodeling occurring during the mineralization and ossification of thyroid cartilage. In fetal and juvenile thyroid cartilages, type I collagen was restricted to the inner and outer perichondrium, while type II collagen was localized in the matrix of hyaline cartilage. However, in advanced ages, type I collagen was also localized in the pericellular and in the interterritorial matrix of intermediate and central chondrocytes of thyroid cartilage. The matrix of peripheral chondrocytes was negative for type I collagen. This suggest that some chondrocytes in thyroid cartilage undergo a differentiation to type I collagen-producing chondrocytes. At the beginning of ossification, bone-related type I collagen was chiefly detected in the central cartilage layer, but was never deposited first from the perichondrium in the direction to the subperichondrial cartilage. This observation confirmed previous findings showing that osteogenesis mainly follows an endochondral ossification pattern. Interterritorial matrix failed to react with the type II collagen antibody in men from the beginning of the third decade, and later still in women, even after treatment with hyaluronidase. These observations indicate that major matrix changes occur faster in male than in female thyroid cartilage.

Adolescent↗