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At least 1,153 records · Page 64Linked to original sources
PubMed1985

[5MHz realtime sonography of the breast. 1. Technical equipment studies].

The resolving characteristics (depth dependence of spatial resolution) of different scanning units are tested by a specially designed tissue-mimicking phantom. The phantom includes cyst-like structures (0.8-5 mm) in several layers. Additional measurements of the lateral resolution (-6 dB beam width) are performed on a spherical test object. The results are compared with regard to the requested imaging depth (visualization of the breast muscle) and the optimum focus zone (depth of pathologic breast lesions) in 307 echomammographic examinations. It is shown that the resolution characteristics and penetration depth of a 5 MHz linear-array-real-time-scanner (LS 3000, Picker Inc.) with special near-range-focus best meet the requirements of breast echography.

Breast Diseases↗
PubMed1985

Effect of instruction and higher level control on the accommodative response spatial frequency profile.

Although the spatial frequency dependence of accommodation is well established, characteristics of the accommodative response profile may vary significantly, thus supporting opposing theories of accommodation control. We demonstrate the pronounced influence of instruction and higher level control on such accommodation profiles. The results suggest that extreme care be taken in the methodological considerations of such experiments, as well as the need for additional systematic investigation of these factors in accommodation studies.

Accommodation, Ocular↗
PubMed1985

Development of stereopsis depends upon contrast sensitivity and spatial tuning.

Various binocular functions such as disparity vergence, and stereopsis develop rapidly during the third to fifth month of life. This time frame coincides with the rapid postnatal development of visual acuity, contrast sensitivity and possibly the tuning of spatial channels. Recent studies of adult stereopsis reveal that small disparities near the stereo threshold are processed within spatial channels tuned above 2.5 cycles/deg. Sensitivity to these higher spatial frequencies develops during the 3-5 months of life. Adult studies also reveal that larger disparities are processed by spatial channels tuned to lower spatial frequencies. Tuning of these low spatial frequency channels may not be present until 3 months of age. Lack of spatial tuning prior to 3 months is predicted to be associated with a lack of disparity tuning as well as an inability to ignore false disparities in ambiguous or redundant stimuli such as random dot stereograms. These observations suggest that refractive anomalies such as anisometropia that limit high frequency spatial resolution and binocular integration can present a major obstacle to the postnatal development of binocular vision.

Adult↗
PubMedDate not supplied

[Effect of blood redistribution on illusional sensations of spatial position in weightlessness].

The study was performed onboard a specially equipped aircraft which allowed zero-g and high-g studies. Blood redistribution was produced using a tilt table (-30 degrees) and a LBNP device. Illusionary sensations were measured by a Birtok unit and subjective reports of the test subjects. In the head-down position the feeling of blood rush to the head disappeared as soon as the weightless state was reached. In most cases illusionary sensations were similar to those in the horizontal position. When exposed to LBNP tests, the subjects developed no illusionary sensations during horizontal flight and felt their upper body going upwards and legs going downwards in the weightless state. Thus, illusionary sensations of the spatial position depend at large on blood redistribution in the human body.

Aerospace Medicine↗
PubMed1993

[Distribution pattern of urothelial associated glycoproteins in human bladder cancer cell lines in in vitro culture].

The distribution of four antibodies against urothelial-associated glycoproteins (UAGAb: Uro1, -5, -9, -10, SIGNET) was studied by dual parameter flow-cytometry (UAGAb and DNA staining) in normal non-urothelial cancer cell lines (2), normal urothelial cell lines (2) and bladder cell lines (5). When cell lines were compared as plateau monolayers, high proportions of Uro1 and Uro10 were found in all cell lines, in contrast to Uro5 and Uro9, both showing specificity for urothelial cells. Though being described as a pan-urothelial marker, Uro5 is not found in all cell lines. In two cell lines (RT4 and J82) three different growth states (exponential and plateau monolayer and multicellular spheroids were compared, and dependence on spatial configuration could be shown for Uro9. Cell cycle relation of expression was found for Uro1 and Uro10.

Cell Line↗
PubMed1997

Constitutive and regulated expression of vitronectin.

Tissue homeostasis depends on spatially and temporally controlled expression of multifunctional adhesive glycoproteins and their cellular counter receptors, and on a tight regulation of proteolytic enzyme systems. The adhesive glycoprotein vitronectin (Vn) not only regulates adhesive events, but also controls a number of these proteolytic enzyme cascades, including the complement, coagulation, and fibrinolytic systems. However, understanding of the biological functions of this molecule is complicated due to it's conformationally lability and its tendency to self-associate. While plasma Vn is monomeric and lacks exposure of conformationally sensitive epitopes, platelet and tissue-associated Vn are believed to be conformationally altered and multimeric. The latter forms express a functional repertoire distinct from plasma Vn. While little Vn immunoreactivity is detectable in most normal tissues, increased depositions of Vn have been observed in areas of tissue injury and necrosis. Tissue Vn was believed to be plasma-derived, but recent studies indicate that extrahepatic cells have the biosynthetic potential to produce Vn and that its synthesis can be regulated under inflammatory conditions. Here, the constitutive and regulated expression of Vn, its locations in tissues and interaction with other matrix molecules are reviewed and their implications for the functions of this molecule are discussed.

Animals↗
PubMed1997

Neurotrophins and cerebellar development.

Neurotrophins are structurally related molecules which regulate the survival and differentiation of various populations of neurons during development. In the cerebellum, the neurotophins and their Trk receptors are expressed at a relatively high level, suggesting an important function for these factors during development. There is also a tight age-dependent and spatial regulation of the molecules in the various cerebellar neurons. Previous studies have shown that BDNF and NT-3 have distinct biological effects on survival and differentiation of cerebellar granule neurons and Purkinje cells. Aside from acting as survival and differentiation factors, the neurotrophins could also have more subtle effects on neuronal function. It is also becoming increasingly evident, not the least from studies in neurotrophin deficient and in cerebellar mutant mice, that the neurotrophins act in concert with other factors and molecules in controlling neuronal development. We will here review some of the recent developments in the neurotrophin field with regard to cerebellum and also discuss what is known about the signaling event following stimulation of cerebellar neurons with BDNF and NT-3. The characterization of specific maturation stages and of genes which are involved and regulated by neurotrophins in developing cerebellum will help us to understand the processes of neuronal survival and differentiation in general.

Animals↗
PubMed2006

Local population size in a flightless insect: importance of patch structure-dependent mortality.

In spatially heterogeneous systems, utilizing population models to integrate the effects of multiple population rates can yield powerful insights into the relative importance of the component rates. The relative importance of demographic rates and dispersal in shaping the distribution of the western tussock moth (Orgyia vetusta) among patches of its host plant was explored using stage-structured population models. Tussock moth dispersal occurs passively in first-instar larvae and is poor or absent in all other life stages. Spatial surveys suggested, however, that moth distribution is not well explained by passive dispersal; moth populations were greater on small patches and on isolated ones. Further analysis showed that several local demographic rates varied significantly with patch characteristics. Two mortality factors in particular may explain the observed patterns. First, crawler mortality both increased with patch size and was density-dependent. A single-patch difference equation model showed mortality related to patch size is strong enough to overcome the homogenizing effect of density dependence; greater equilibrium densities were predicted for smaller patches. Second, although three rates were found to vary with local patch density, only pupal parasitism by a chalcid wasp could potentially account for higher moth abundances on isolated patches. A spatially explicit simulation model of the multiple-patch system showed that spatial variation in pupal parasitism is indeed strong enough to generate such a pattern. These results demonstrate that habitat spatial structure can affect multiple population processes simultaneously, and even relatively low attack rates imposed on a reproductively valuable life stage of the host can have a dominant effect on population distribution among habitat patches.

Animals↗
PubMed2005

Spatial memory in the rat requires the dorsolateral band of the entorhinal cortex.

The extensive connections of the entorhinal cortex with the hippocampus and the neocortex point to this region as a major interface in the hippocampal-neocortical interactions underlying memory. We asked whether hippocampal-dependent recall of spatial memory depends on the entorhinal cortex, and, if so, which parts are critical. After training in a Morris water maze, rats received fiber-sparing lesions in the dorsolateral band of the entorhinal cortex, which mediates much of the visuospatial input to the dorsal hippocampus. These lesions entirely disrupted retention and retarded new learning. Spatial memory was spared by lesions in the ventromedial band, which connects primarily with ventral hippocampus, but these lesions reduced defensive behavior on an elevated plus maze, mirroring the effects of damage to ventral hippocampus. The results suggest that the functional differences between dorsal and ventral hippocampus reflect their connectivity with modules of the entorhinal cortex that are differently linked to the rest of the cortex.

Animals↗
PubMed2005

Global shape recognition is modulated by the spatial distance of local elements--evidence from simultanagnosia.

Simultanagnosia is a rare deficit that impairs individuals in perceiving several objects at the same time. It is usually observed following bilateral parieto-occipital brain damage. Despite the restrictions in perceiving the global aspect of a scene, processing of individual objects remains unaffected. The mechanisms underlying simultanagnosia are not well understood. Previous findings indicated that the integration of multiple objects into a holistic representation of the environment is not impossible per se, but might depend on the spatial relationship between individual objects. The present study examined the influence of inter-element distances between individual objects on the recognition of global shapes in two patients with simultanagnosia. We presented Navon hierarchical letter stimuli with different inter-element distances between letters at the Local Scale. Improved recognition at the Global Scale was observed in both patients by reducing the inter-element distance. Global shape recognition in simultanagnosia thus seems to be modulated by the spatial distance of local elements and does not appear to be an all-or-nothing phenomenon depending on spatial continuity. The findings seem to argue against a deficit in visual working memory capacity as the primary deficit in simultanagnosia. However, further research is necessary to investigate alternative interpretations.

Agnosia↗
PubMed1998

Excitotoxic lesions centered on perirhinal cortex produce delay-dependent deficits in a test of spatial memory.

Rats with bilateral electrolytic or ibotenic acid lesions that were centred in perirhinal cortex displayed a significant delay-dependent deficit on a delayed nonmatch to position task in the T maze. Although the removal of prominent extramaze visual cues did not affect the performance of these rats, rotating the maze between the sample and test phases did, indicating that rats were using a spatial strategy. Interestingly, a further group of rats with hippocampal and perirhinal damage displayed deficits that may reflect a dysfunction in the use of inertial cues. These results suggest that both electrolytic and excitotoxic lesions of perirhinal cortex produce spatial memory impairments but that these impairments are qualitatively different than those exhibited following hippocampal damage.

Analysis of Variance↗
PubMed2004

Index for spatial heterogeneity in breast cancer.

Histopathological heterogeneity in cancer is a general concern. Breast carcinoma heterogeneity is now widely admitted as a source of histological grading imprecision and reproducibility problems. Classically, homogeneity is defined as equivalent to stationarity. A measure of heterogeneity based on asymptotic properties of spatial statistics is developed. Long-range dependences in heterogeneous spatial processes make estimation of the proposed heterogeneity measure unreliable. A robust estimator based on the wavelet transform is presented; this bypasses long-range dependences. The estimator extends previous works on one-dimensional stochastic processes to two dimensions as appropriate for histopathological analysis. As a side result, the estimator gives confidence intervals for the heterogeneity measure that enables the formulation and validation of testable hypothesis on the observed histopathological samples. This approach is applied to the characterization of breast cancer tumours. We show that the heterogeneity measure for various blocks of a single tumour is invariable, even when various blocks differ in size and in number of marked nuclei.

Breast Neoplasms↗
PubMed1985

Another visual illusion involving orientation.

The orientation of a grating may be misperceived when that grating appears superimposed within one-dimensional visual noise of a different orientation. An adjustment procedure was employed to measure the size of this tilt illusion and its dependence on noise orientation. The illusion is maximum when the noise and test differ by 20 to 40 deg, depending on the spatial frequency of the test grating. Noise composed of spatial frequencies several octaves removed from the test spatial frequency can still cause illusory tilt, although the degree of tilt under these conditions depends on test spatial frequency. This orientation illusion, like the tilt aftereffect, simultaneous tilt illusion and angle expansion illusion, may reflect inhibitory interactions between orientation selective neurons in human vision.

Female↗
PubMed1997

Experience-dependent facilitating effect of corticosterone on spatial memory formation in the water maze.

Stress-related adrenal steroid hormones modulate brain and cognitive function. Electrophysiological studies, including primed burst potentiation and long-term potentiation, have indicated concentration-dependent inverted U-shape effects of corticosterone in hippocampal function and plasticity. Here, we explored the role of corticosterone in the consolidation and long-term retrieval of spatial learning in the Morris water maze task in rats. We postulated that corticosterone actions might be experience-dependent with regard to stimulus intensity, such as differential water temperatures. Indeed, rats trained at 19 degrees C showed a quicker rate of acquisition and better long-term retention than rats trained at 25 degrees C water. In addition, post-training corticosterone levels, on the first training day, were significantly higher in rats in the 19 degrees C group than in the 25 degrees C group. Performance of rats trained at 25 degrees C, but not at 19 degrees C, water was improved by injecting them i.p. with corticosterone immediately after each training session. Thus, the effect of exogenously administered corticosterone appears to be experience-dependent, with the experience-induced corticosterone concentrations as a critical factor determining the cognitive consequences of steroid treatment. Therefore, this work indicates a facilitating corticosterone action, during the post-training period, on the neural mechanisms determining the strength of information storage under acute, physiological conditions.

Analysis of Variance↗
PubMed1989

Spatial selectivity of rat hippocampal neurons: dependence on preparedness for movement.

The mammalian hippocampal formation appears to play a major role in the generation of internal representations of spatial relationships. In rats, this role is reflected in the spatially selective discharge of hippocampal pyramidal cells. The principal metric for coding spatial relationships might be the organism's own movements in space, that is, the spatial relationship between two locations is coded in terms of the movements executed in getting from one to the other. Thus, information from the motor programming systems (or "motor set") may contribute to coding of spatial location by hippocampal neurons. Spatially selective discharge of hippocampal neurons was abolished under conditions of restraint in which the animal had learned that locomotion was impossible. Therefore, hippocampal neuronal activity may reflect the association of movements with their spatial consequences.

Animals↗
PubMed1988

Fertilization alters the spatial distribution and the density of voltage-dependent sodium current in the egg of the ascidian Boltenia villosa.

The spatial distribution of voltage-dependent ionic currents was characterized in Boltenia villosa eggs before and after fertilization using two-microelectrode voltage clamp of paired animal-vegetal halves of eggs (merogones) made surgically. Major voltage-dependent conductances in the Boltenia egg are a transient inward Na current, a transient inward Ca current, and an inwardly rectifying K current. These currents were randomly distributed along the animal-vegetal axis in the unfertilized egg. When paired merogones (surgically prepared egg fragments) were made at the vegetal cap stage, 15-30 min after fertilization, Ca and K currents remained randomly distributed along the animal-vegetal axis. In contrast, the relative Na current density was found to be twofold lower in the vegetal vs the animal merogones made at the vegetal cap stage. By making pairs of merogones from unfertilized eggs and subsequently fertilizing one merogone of a pair, we showed that this change in current density ratio was due to a loss of absolute Na current density in the vegetal hemisphere shortly after fertilization. These results also show that this loss was intrinsic to the vegetal hemisphere, rather than being determined solely by the point of sperm entry. A second decrease in Na current was observed during the hour before first cleavage, 60-120 min after fertilization (M.L. Block and W.J. Moody, 1987, J. Physiol. 393, 619-634), both in fertilized eggs and in animal merogones fertilized after isolation. This second loss of Na current was not observed in vegetal merogones fertilized after isolation or in either animal or vegetal merogones made from fertilized eggs at the vegetal cap stage. Possible mechanisms for te rapid (complete by 40 min after fertilization) and the late (occurring from ca. 60 to 120 minutes after fertilization) Na current losses are discussed.

Action Potentials↗
PubMed1991

Evidence against a specific effect of cholinergic drugs on spatial memory in primates.

A scopolamine-like delay-dependent impairment in spatial delayed response performance in rhesus monkeys was induced by irrelevant interpolated activity or by using extended retention intervals. Physostigmine readily reversed the effects of scopolamine but had no effect on performance in young monkeys performing an irrelevant distractor task or in monkeys tested using extended retention intervals. Reducing stimulus control did not impair performance and did not alter the dose-response curve for induction of a deficit by scopolamine. Reducing the stimulus presentation time impaired performance across all retention intervals in a way which did not resemble the effect of scopolamine and which disappeared with practice. Our findings do not support the proposal that physostigmine interacts specifically with short-term spatial memory in primates.

Animals↗