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Results for “spatial localization”

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At least 181 records · Page 10Linked to original sources
PubMed1996

Extraocular proprioception is required for spatial localization in man.

We studied the effect of extraocular muscle deafferentation on the performance of manual pointing to foveated visual targets at different craniotopic locations. Five patients who underwent unilateral thermocoagulation of the trigeminal nerve (V) for trigeminal neuralgia were tested before and after surgery. Only the group of patients with postsurgical corneal anaesthesia, attesting to involvement of the ophthalmic branch (which carries the ocular proprioceptive fibres), presented deficits in accuracy of pointing. The position of initial and final pointing was shifted toward the lesioned side predominantly in the ipsilateral hemispace. These data support a model in which balanced ocular proprioceptive inputs are required for accuracy of visually guided movements in egocentric space.

Afferent Pathways↗
PubMed1999

The effects of local spatial structure on epidemiological invasions.

Predicting the likely success of invasions is vitally important in ecology and especially epidemiology. Whether an organism can successfully invade and persist in the short-term is highly dependent on the spatial correlations that develop in the early stages of invasion. By modelling the correlations between individuals, we are able to understand the role of spatial heterogeneity in invasion dynamics without the need for large-scale computer simulations. Here, a natural methodology is developed for modelling the behaviour of individuals in a fixed network. This formulation is applied to the spread of a disease through a structured network to determine invasion thresholds and some statistical properties of a single epidemic.

Communicable Disease Control↗
PubMed1993

Differential responses of single reticulospinal cells to spatially localized stimulation of the optic tectum in a teleost fish, Salmo trutta.

To determine whether the topographically organized retinal input to the optic tectum is subsequently mapped onto the reticular formation, the responses of antidromically identified reticulospinal cells to tectal surface stimulation were investigated in 45 decerebrated, paralysed trout. The tectum was stimulated through a silver ball surface electrode at 24 different locations, and extracellular recordings were made from the rhombencephalic brainstem with glass microelectrodes filled with a 10% solution of horseradish peroxidase (HRP) in Tris buffer (pH 7.4). After recording, the HRP was, in some cases, iontophoretically expelled from the pipette to identify its location and visualized in histological sections by a modified Hanker-Yates method. Individual reticulospinal neurons discharged 1-4 spikes at short latency in response to stimulation of each of the 24 tectal locations. From one tectal location per cell, this initial response was followed by a late, sustained burst. With a short stimulus train (6 pulses, 55 Hz) the burst could last for over a second with discharge rates of up to 500 Hz. Sometimes this burst could be evoked from neighbouring tectal locations, but only by greatly increasing the stimulus strength. We conclude that the reticular formation receives a highly divergent monosynaptic connection from all locations of the tectum and that the longer latency, sustained burst response is due to a mapped connection between the tectum and the reticular formation. Since the late burst could be preceded by a silent period lasting for approximately 32 ms, we cannot rule out a dependence on interneurons situated between the tectum and the reticulospinal cells.

Animals↗
PubMed2003

Spatial localization of cardiac optical mapping with multiphoton excitation.

Depth and radius of regions interrogated by cardiac optical mapping with a laser beam depend on photon travel inside the heart. It would be useful to limit the range of depth and radius interrogated. We modeled the effects of a condensing lens to concentrate laser light at a target depth inside the heart, and near infrared excitation to increase penetration and produce two-photon absorption. A Monte Carlo simulation that incorporated a 0.55-NA lens, and absorption and scattering of 1064- or 488-nm laser light in 3-D cardiac tissue indicated the distribution of excitation fluence inside the tissue. A subsequent simulation incorporating absorption and scattering of transmembrane voltage-sensitive fluorescence (wavelength 669 nm) indicated locations from which fluorescence photons exiting the tissue surface originated. The results indicate that mapping at depths up to 300 microm in hearts can provide significant improvement in localization over existing cardiac optical mapping. The estimated interrogation region is sufficiently small to examine cardiac events at a cellular or subcellular scale and may allow mapping at various depths in the heart.

Action Potentials↗
PubMed1981

Spatial localization after strabismus surgery: evidence for inflow.

Strabismics pointed to targets (without sight of the hand) before and again after surgery that altered the position of the deviating eye in its orbit. Patients having this surgery for the first time were able to use proprioceptively derived information about the surgically altered eye position. In contrast, patients who had similar operations, but on muscles that had been operated on one or more times in the past, were apparently deprived of this information. The important afference may be supplied by the tendon organs.

Afferent Pathways↗
PubMed1991

Identification, characterization, and spatial localization of two flagellin species in Helicobacter pylori flagella.

Flagellar filaments were isolated from Helicobacter pylori by shearing, and flagellar proteins were further purified by a variety of techniques, including CsCl density gradient ultracentrifugation, pH 2.0 acid disassociation-neutral pH reassociation, and differential ultracentrifugation followed by molecular sieving with a Sephacryl S-500 column or Mono Q anion-exchange column, and purified to homogeneity by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transfer to an Immobilon membrane. Two flagellin species of pI 5.2 and with apparent subunit molecular weights (Mrs) of 57,000 and 56,000 were obtained. N-terminal amino acid analysis showed that the two H. pylori flagellin species were related to each other and shared sequence similarity with the N-terminal amino acid sequence of Campylobacter coli, Bacillus, Salmonella, and Caulobacter flagellins. Analysis of the amino acid composition of the predominant 56,000-Mr flagellin species isolated from two strains showed that it was comparable to the flagellins of other species. The minor 57,000-Mr flagellin species contained a higher content of proline. Immunoelectron microscopic studies with polyclonal monospecific H. pylori antiflagellin antiserum and monoclonal antibody (MAb) 72c showed that the two different-Mr flagellin species were located in different regions of the assembled flagellar filament. The minor 57,000-Mr species was located proximal to the hook, and the major 56,000-Mr flagellin composed the remainder of the filament. Western immunoblot analysis with polyclonal rabbit antisera raised against H. pylori or Campylobacter jejuni flagellins and MAb 72c showed that the 56,000-Mr flagellin carried sequences antigenetically cross-reactive with the 57,000-Mr H. pylori flagellin and the flagellins of Campylobacter species. This antigenic cross-reactivity did not extend to the flagellins of other gram-negative bacteria. The 56,000-Mr flagellin also carried H. pylori-specific sequences recognized by two additional MAbs. The epitopes for these MAbs were not surface exposed on the assembled inner flagellar filament of H. pylori but were readily detected by immunodot blot assay of sodium dodecyl sulfate-lysed cells of H. pylori, suggesting that this serological test could be a useful addition to those currently employed in the rapid identification of this important pathogen.

Amino Acid Sequence↗
PubMed1980

Spatial localization in cats reared with strabismus.

1. The capacity for judging the location of an object relative to the body (egocentric localization) was assessed in cats by measuring the landing position attained when the cat jumped toward a platform viewed from a known distance. 2. Normal cats and kittens land at center of the platform when using one eye or both. In contrast, nine animals tested immediately after tenotomy of the medial rectus muscle of one eye all landed consistently off-center when using the operated eye. The direction of the error was predictable from the assumption that the cat was unaware of the eye's deviation from its natural position. Thus, proprioceptive reafference is not capable, under these conditions, of supporting an accurate awareness of eye position. 3. After initial testing, all cats were maintained in a normal environment with both eyes open and were tested intermittently. Jumps guided by the deviated eye became accurate over a period of weeks in kittens younger than 4 mo. In contrast, behavioral adjustment in older kittens required many months. An adult cat displayed almost no adjustment over a period of 9 mo. 4. Five additional kittens were first tested several months after the onset of strabismus. These animals manifested accurate use of the operated eye from the first trial onward. Therefore, acquisition of accurate use of the deviated eye is not dependent on repeated testing. 5. Two kittens subjected to early exodeviation of one eye displayed a reduced capacity for adjustment when subjected to late exodeviation of the second eye. Thus, changes in neural function resulting from early strabismus (for instance, the loss of binocular connectivity in striate cortex) do not produce persistent behavioral flexibility. 6. In two strabismic kittens with a fully developed compensatory adjustment of monocular egocentric localization, the capacity for judging the relative location of two objects viewed simultaneously through separate eyes was assessed through use of a two-choice visual discrimination paradigm. One animal made predictable systematic errors, while the other exhibited correct judgments. Thus, it appears that a compensatory shift of retinal correspondence may occur in some strabismic kittens, but that such a change is not necessary for accurate use of the deviated eye in monocular visual guidance. 7. A number of observations are described that tend to indicate that cats reared with strabismus continue to use both the deviated and the nondeviated eye for visual guidance under binocular viewing conditions, unlike many human strabismics.

Adaptation, Physiological↗
PubMed1997

Perceptual learning of spatial localization: specificity for orientation, position, and context.

Discrimination of simple visual attributes can improve significantly with practice. We have trained human observers to perform peripherally presented tasks involving the localization of short line segments and examined the specificity of the learning for the visual location, orientation, and geometric arrangement of the trained stimulus. Several weeks of training resulted in dramatic threshold reductions. The learning was specific for the orientation and location of the trained stimulus, indicating the involvement of the earliest cortical stages in the visual pathway where the orientation and location of stimuli are mapped with highest resolution. Furthermore, improvement was also specific for both the configuration of the trained stimulus and the attribute of the stimulus that was under scrutiny during training. This degree of specificity suggests that the learning cannot be achieved by cortical recruitment alone, as proposed in current models, but is likely to involve a refinement of lateral interactions within the cortex and possibly a gating of lower level changes by attentional mechanisms.

Cues↗