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Results for “Optical mapping”

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At least 613 records · Page 34Linked to original sources
PubMed2002

Global quantitative predictions of complex laser dynamics.

We demonstrate unprecedented agreement between a theoretical two-dimensional bifurcation diagram and the corresponding experimental stability map of an optically injected semiconductor laser over a large range of relevant injection parameter values. The bifurcation diagram encompasses both local and global bifurcations mapping out regions of regular, chaotic, and multistable behavior in considerable detail. This demonstrates the power of dynamical systems modeling for the quantitative prediction of nonlinear dynamics and chaos of semiconductor lasers.

Journal Article↗
PubMed1993

Things that go bump in the light: on the optical specification of contact severity.

Psychologists are intrigued with the idea that optical variables can specify not only the time until an object impacts an observer but also the severity of the impact. However, the mapping between the optical variables (tau and .tau) and the kinematic variables (velocity, acceleration) has been misstated, erroneously implying that there exist critical values of the optical variables used for locomotion and control. In this commentary, the mathematical relationship between the optical and kinematic variables is reexamined and the erroneous assumptions that have led to the proposal of critical values are show. Also examined are the empirical data on deceleration to approach (particularly from active control paradigms) to assess whether the proposed optical variables are likely candidates for control strategies. Finally, problems associated with numerical approximations to dynamic systems, particularly when analytic solutions exist, are discussed.

Acceleration↗
PubMed2002

Structure-assigned optical spectra of single-walled carbon nanotubes.

Spectrofluorimetric measurements on single-walled carbon nanotubes (SWNTs) isolated in aqueous surfactant suspensions have revealed distinct electronic absorption and emission transitions for more than 30 different semiconducting nanotube species. By combining these fluorimetric results with resonance Raman data, each optical transition has been mapped to a specific (n,m) nanotube structure. Optical spectroscopy can thereby be used to rapidly determine the detailed composition of bulk SWNT samples, providing distributions in both tube diameter and chiral angle. The measured transition frequencies differ substantially from simple theoretical predictions. These deviations may reflect combinations of trigonal warping and excitonic effects.

Journal Article↗
PubMedDate not supplied

Optical imaging of orientation and ocular dominance maps in area 17 of cats with convergent strabismus.

Strabismus (or squint) is both a well-established model for developmental plasticity of the brain and a frequent clinical symptom. While the layout and topographic relationship of functional domains in area 17 of divergently squinting cats has been analyzed extensively in recent years (e.g. Löwel et al., 1998), functional maps in convergently squinting animals have so far not been visualized with comparable detail. We have therefore investigated the functional organization of area 17 in adult cats with a surgically induced convergent squint angle. In these animals, visual acuity was determined by both behavioral tests and recordings of visual evoked potentials, and animals with comparable acuities in both eyes were selected for further experiments. The functional layout of area 17 was visualized using optical imaging of intrinsic signals. Monocular iso-orientation domains had a patchy appearance and their layout was different for left and right eye stimulation, so that segregated ocular dominance domains could be visualized. Iso-orientation domains exhibited a pinwheel-like organization, as previously described for normal and divergently squinting cats. Mean pinwheel density was the same in the experimental and control animals (3.4 pinwheel centers per mm2 cortical surface), but significantly (P < 0.00001) higher than that reported previously for normal and divergently squinting cats (2.7/mm2). A comparison of orientation with ocular dominance maps revealed that iso-orientation domains were continuous across the borders of ocular dominance domains and tended to intersect these borders at steep angles. However, in contrast to previous reports in normally raised cats, orientation pinwheel centers showed no consistent topographical relationship to the peaks of ocular dominance domains. Taken together, these observations indicate an overall similarity between the functional layout of orientation and ocular dominance maps in area 17 of convergently and divergently squinting cats. The higher pinwheel densities compared with previous reports suggest that animals from different gene pools might generally differ in this parameter and therefore also in the space constants of their cortical orientation maps.

Animals↗
PubMedDate not supplied

Mapping functional activity in rodent cortex using optical intrinsic signals.

We have investigated the dynamic response of rodent posteromedial barrel subfield (PMBSF) cortex to mechanical whisker deflection, using optical intrinsic signal imaging. While electrophysiologic response in barrel cortex has been well studied, dynamic metabolic changes affecting activity-related perfusion or oxidative enzymes are not well understood. Male Sprague-Dawley rats were anesthetized. Contralateral single and multiple vibrissae were deflected while images of somatosensory cortex were acquired with a charge-coupled-device camera. Intrinsic signals were observed over PMBSF as stimulus-related reflectance decreases (10(-3) of baseline) comprising two distinct spatiotemporal components. At 610 nm the first, diffuse, component begins 0.5-1 sec after stimulus onset, peaks at 2.5-3 sec, and returns to baseline by 4-5 sec. The second component is macrovascular, beginning at 1-1.5 sec, peaking at 3 sec, and dissipating by 5-6 sec. Similar patterns were observed at 550 nm and 850 nm. Signal size and location varied with the stimulus. Evoked potentials were found to have maximal amplitude in the region of maximal optical signals, diminishing toward the optical periphery. We have demonstrated PMBSF response to vibrissal deflection using optical reflectance methods. These intrinsic signals overlie regions of maximal electrophysiologic response, but commence, peak, and extinguish over a time scale of seconds from stimulus onset. They most likely indicate activity-related microvascular recruitment and chromophore redox changes.

Animals↗
PubMedDate not supplied

[Optic methods for measurements of muscle fiber birefringence].

An optical method for measuring the birefringence of muscle fibers was developed, which is realized on an automated Linnick interferometer microscope equipped with a laser. It was shown that the method has some advantages over the methods based on measurements of the intensity of light passing through a crossed polarizer, an analyzer, and a fiber (light polarized microscopy). The method involves direct phase measurements of optical path length at the parallel and perpendicular orientations of the polarization plane of probing radiation. The phase image is reconstructed automatically from interferograms with the use of the four-frame phase-shifting algorithm. The phase images of one and the same central part of the fiber at different orientations of the polarization plane represent two-dimensional numerical maps of the optical path length. The subtraction of these images gives a two-dimensional map of the phase shift, which includes information about the birefringence of the fiber. A formula for birefringence measurements was deduced, which has a certain advantage in comparison to that used earlier in that it does not take into account the thickness of a fiber that depends on the measurement point. The birefringence is normalized to a value of the half sum of phases, which are measured separately in the course of the experiment.

Algorithms↗
PubMed2004

Molecular genetic basis of primary inherited optic neuropathies.

AIM: To review the molecular genetic basis of primary inherited optic neuropathies. METHODS: Medline and Embase search. RESULTS: Inherited optic neuropathies are a genetically diverse group of disorders that present with reduced visual acuity and the clinical appearance of optic atrophy. The inherited optic neuropathies may be sporadic or familial, in which case the mode of inheritance may be Mendelian (autosomal dominant, autosomal recessive, X-linked recessive) or non-Mendelian (mitochondrial). Two genes for dominantly inherited optic atrophy have been mapped (OPA1 and OPA4), of which the gene has been identified in one (OPA1). A gene for recessive optic atrophy (OPA3) has also been identified. X-linked optic atrophy (OPA2) has been mapped but to date no gene has been identified. Mutations in mitochondrial DNA have been identified in Leber's hereditary optic neuropathy. CONCLUSIONS: Mutations in genes from both the nuclear and mitochondrial genomes appear to be responsible. Mitochondrial dysfunction, in the broadest sense, is emerging as central to the pathogenesis of this group of conditions.

GTP Phosphohydrolases↗
PubMed2005

Chronic melatonin and binocular plasticity in Xenopus frogs.

The topographic binocular maps in the optic tectum of Xenopus frogs are notable both for their dramatic plasticity during development and for the high expression of melatonin receptors in the circuitry contributing to those binocular maps. The goal of this study was to determine whether melatonin contributes to the control of binocular tectal plasticity. During development, rotation of one eye leads to compensatory rewiring of ipsilateral maps. The effect of 3-4 months of chronic 20 or 200 nM melatonin on this rewiring was tested by electrophysiological mapping. No decrease in plasticity was observed. In adult Xenopus, rotation of one eye normally does not lead to rewiring of the ipsilateral projection, although adults can exhibit plasticity if they have been dark-reared or have been treated as adults with NMDA. We tested whether exposure to 20-200 nM melatonin during and after the normal critical period would similarly extend plasticity. Eye rotation in adults that had been treated with melatonin did not demonstrate retained plasticity. These results show that melatonin does not reduce the normally high plasticity characteristic of young Xenopus nor does it increase the normally low plasticity of adult Xenopus.

Animals↗
PubMed1983

Space-mapped auditory projections from the inferior colliculus to the optic tectum in the barn owl (Tyto alba).

The optic tectum of the owl contains a topographic representation of auditory space. We have investigated the source of this space-mapped auditory activity by using retrograde tracing with horseradish peroxidase. The major source of auditory input to the optic tectum is the ipsilateral external nucleus of the inferior colliculus (ICX), which is known to contain a map of auditory space also. Additional minor projections originate in the superficial nucleus of the inferior colliculus and the nucleus isthmi parvocellularis. There is no apparent projection to the optic tectum from the contralateral ICX or any other brainstem auditory nucleus. The projection from the ICX to the optic tectum is point-to-point: rostral ICX projects to rostral tectum, caudal ICX to caudal tectum, dorsal ICX to dorsomedial tectum, and ventral ICX to ventral tectum. Thus, the space-mapped organization that exists in the ICX is passed on by topographic projections to the optic tectum.

Animals↗
PubMed2006

Dynamic shifts in the owl's auditory space map predict moving sound location.

The optic tectum of the barn owl contains a map of auditory space. We found that, in response to moving sounds, the locations of receptive fields that make up the map shifted toward the approaching sound. The magnitude of the receptive field shifts increased systematically with increasing stimulus velocity and, therefore, was appropriate to compensate for sensory and motor delays inherent to auditory orienting behavior. Thus, the auditory space map is not static, but shifts adaptively and dynamically in response to stimulus motion. We provide a computational model to account for these results. Because the model derives predictive responses from processes that are known to occur commonly in neural networks, we hypothesize that analogous predictive responses will be found to exist widely in the central nervous system. This hypothesis is consistent with perceptions of stimulus motion in humans for many sensory parameters.

Adaptation, Physiological↗
PubMed2002

Automatic fusion of freehand endoscopic brain images to three-dimensional surfaces: creating stereoscopic panoramas.

A major limitation of the use of endoscopes in minimally invasive surgery is the lack of relative context between the endoscope and its surroundings. The purpose of this work was to fuse images obtained from a tracked endoscope to surfaces derived from three-dimensional (3-D) preoperative magnetic resonance or computed tomography (CT) data, for assistance in surgical planning, training and guidance. We extracted polygonal surfaces from preoperative CT images of a standard brain phantom and digitized endoscopic video images from a tracked neuro-endoscope. The optical properties of the endoscope were characterized using a simple calibration procedure. Registration of the phantom (physical space) and CT images (preoperative image space) was accomplished using fiducial markers that could be identified both on the phantom and within the images. The endoscopic images were corrected for radial lens distortion and then mapped onto the extracted surfaces via a two-dimensional 2-D to 3-D mapping algorithm. The optical tracker has an accuracy of about 0.3 mm at its centroid, which allows the endoscope tip to be localized to within 1.0 mm. The mapping operation allows multiple endoscopic images to be "painted" onto the 3-D brain surfaces, as they are acquired, in the correct anatomical position. This allows panoramic and stereoscopic visualization, as well as navigation of the 3-D surface, painted with multiple endoscopic views, from arbitrary perspectives.

Algorithms↗
PubMed2002

Epitope-mapping of transglutaminase with parallel label-free optical detection.

The gastrointestinal disorder coeliac disease (CD) is induced by the ingestion of wheat gluten and is characterized by damage of the typical structure of the intestinal mucosa. The enzyme tissue transglutaminase (tTGase) was identified as the major target of disease-specific antibodies in-patients. We performed an epitope fine-mapping with a series of pentadecapeptides synthesized using parallel multiple peptide synthesis. For the detection of biomolecular interactions a label-free parallel method, reflectometric interference spectroscopy (RIfS), was used. This is the first optical label-free method adapted to a high throughput screening (HTS) format and the experimental results demonstrate its applicability as a biological screening device. A high titer of anti-tTGase antibodies is found in the serum of coeliac patients. We have taken the first step towards a fast non-surgical test for the detection of these antibodies. In order to identify and characterize a continuous epitope with high affinity against the anti-tTGase antibody a screening of 21 pentadecapeptides has been accomplished with the parallel RIfS system. A single channel RIfS-system with high resolution was used to determine binding constants of identified peptides with high affinity.

Animals↗
PubMed1999

Theory of circle maps and the problem of one-dimensional optical resonator with a periodically moving wall.

We consider the electromagnetic field in a cavity with a periodically oscillating perfectly reflecting boundary and show that the mathematical theory of circle maps leads to several physical predictions. Notably, well-known results in the theory of circle maps (which we review briefly) imply that there are intervals of parameters where the waves in the cavity get concentrated in wave packets whose energy grows exponentially. Even if these intervals are dense for typical motions of the reflecting boundary, in the complement there is a positive measure set of parameters where the energy remains bounded.

Journal Article↗
PubMed2005

[Diagnostic laser in glaucoma: scanning laser polarimetry (GDx VCC) and confocal scanning laser tomography (HRT)].

Automated structural measurements of retinal nerve fibers and optic nerve head are possible with new lasers providing objective and reproductible data for analysis. Scanning laser polarimetry (GDx VCC), based on retardation of polarized light, assesses peripapillary nerve fiber layer thickness. Confocal scanning laser tomography yields precise topographic maps of the optic disc and peripapillary retina. The advantages, applications for glaucoma detection, both in a screening setting as well as for monitoring progression, limitations and pitfalls need to be well known and results should be analyzed with clinical data.

Disease Progression↗
PubMed1992

mip causes hyperinnervation of a retinotopic map in Drosophila by excessive recruitment of R7 photoreceptor cells.

The two central photoreceptor neurons of the Drosophila eye, R7 and R8, form a retinotopic map in the optic lobe of the fly brain. We have developed a technique that allows us to visualize the projections of these neurons with high resolution. Using this technique, we have identified a new mutant, mip (more inner photoreceptors), in which this map shows a striking hyperinnervation. The extra terminals in the brain derive from an excessive recruitment of sevenless-independent R7 photoreceptor cells during eye development. The original R7, however, remains sevenless responsive. The behavior of this gene suggests that recruitment to the R7 pathway, and possibly to multiple programs in ommatidial assembly, is partially regulated by inhibition.

Alleles↗
PubMed1990

Dynamic changes in optic fiber terminal arbors lead to retinotopic map formation: an in vivo confocal microscopic study.

Dynamic remodeling of retinal ganglion cell terminal arbors has been proposed to contribute to formation of the topographically ordered retinotectal projection. To test this directly, the growth of individual terminal arbors was observed in live X. laevis tadpoles using a confocal microscope to visualize their complex three-dimensional structure. During initial development, nasal and temporal retinal arbors covered overlapping tectal areas. Despite subsequent remodeling, the dimensions and positions of the temporal arbors remained relatively stable. In contrast, the nasal arbors grew caudally, as they extended caudal branches and retracted rostral branches. These results suggest that differences in the remodeling of the nasal and temporal arbors lead to the emergence of retino-topography along the rostrocaudal axis of the tectum. All the terminal arbors were dynamic, including those with stable dimensions, suggesting that continual remodeling of arbors may be a universal feature of neuronal projections.

Animals↗
PubMedDate not supplied

Dose mapping of porcine coronary arteries using an optical fiber dosimeter.

BACKGROUND: This study is about the measurement of radiation dose contribution to the coronary arteries during intravascular brachytherapy with beta and gamma emitters utilizing in vivo optical fiber dosimeters. METHODS AND MATERIALS: Domestic pigs were used. With each measurement, catheters were introduced into two different coronary arteries, including the left circumflex (LCX), the left anterior descending (LAD), the first diagonal, and/or the right coronary artery (RCA). A radioactive source (192Ir, 90Sr/Y, or 32P) and the dosimeter were loaded in each of these catheters. Data were collected as the dosimeter was being retracted at a constant rate via computer control. RESULTS: The radiation dose was normalized to 100% at a 2-mm radial distance from the source. When radiating a branching artery, the dose to the bifurcation at 5 mm from the source was 35%, 10%, and 3% for the 192Ir (10 seeds), 90Sr/Y (40 mm), and 32P sources, respectively. When utilizing a 23-seed 192Ir source, the dose is 40% at a 5-mm distance. However, radiation of the RCA did not result in dosing to the LAD or LCX using any source. CONCLUSIONS: The dose to adjacent artery segments is less with beta than with gamma emitters. Significant dose exposition is noted when using gamma emitters at a distance of 5 mm. The results can serve as a guideline for establishing prescription doses and safety margins for the treatment of bifurcation lesions and retreatment of the arteries.

Animals↗
PubMed2004

Building a projection map for photoreceptor neurons in the Drosophila optic lobes.

The sensory tasks performed by the eye are diverse and complex. In Drosophila, the eye performs motion detection for navigation as well as detection of the quality of light (color and polarized light). Both types of inputs are processed separately, as different photoreceptors are specialized in these tasks and contact different target cell layers in the optic lobe. However, their respective outputs are likely to be integrated in higher brain centers. Here, we discuss the cell diversity and potential role of the several ganglia that form the fly optic lobe. We also discuss the power of modern genetic tools to provide the potential to trace the visual neural networks.

Animals↗