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At least 1,657 records · Page 92Linked to original sources
PubMed2001

Brief visual stimulation allows mapping of ocular dominance in visual cortex using fMRI.

We have used high spatial resolution (0.55 mm x 0.55 mm) functional magnetic resonance imaging (fMRI) to show that when stimulus duration is brief (<6 sec), the hyperoxic hemodynamic response to neural activity can resolve the columnar architecture of ocular dominance within the primary visual cortex of humans. Our fMRI maps of ocular dominance columns are strikingly similar in appearance, size, and orientation to those reported in the literature using optical imaging of intrinsic signals (OIS) in animal cortex and histology of post-mortem human specimens. We also demonstrate that under brief visual stimulation conditions, our results are consistent over repeated experiments. This is not the case for long duration stimuli (> or = 10 sec). A simulated random data set exhibited the same response properties as maps obtained when using these prolonged visual stimuli. Our results suggest that brief visual stimulation is essential for fMRI to successfully resolve ocular dominance columns using the hyperoxic phase of the hemodynamic response to neural activity at our prescribed spatial resolution.

Brain Mapping↗
PubMed2006

Optical imaging of dose distributions in Fricke gels.

Ferrous-sulphate infused gels, or 'Fricke gels', encounter great interest in the field of radiation dosimetry, due to their potential for 3D radiation dose mapping. Typically, magnetic resonance (MR) relaxation rates are determined in these systems in order to derive the absorbed dose. However, when large concentration gradients are present, diffusion effects before and during the MR imaging may not be negligible. In these cases, optical techniques may represent a viable alternative. This paper describes research aimed at measuring 3D dose distributions in a Fricke-xylenol orange gel by measuring optical density with a CCD camera. This method is inexpensive and fast. A series of early experiments is described, in which optical density profiles were measured with a commercial microdensitometer for film dosimetry. The light box of the device was modified to work at 567 nm, close to the maximum absorbance of the ferric ion-xylenol orange complex. Under these conditions, the gel shows linearity with dose and high sensitivity.

Dose-Response Relationship, Radiation↗
PubMed2000

An optical model of the human retinal nerve fiber layer: implications of directional reflectance for variability of clinical measurements.

PURPOSE: The reflectance of the retinal nerve fiber layer is highly directional--that is, it depends strongly on the angles of illumination and viewing. This study explored and illustrated the implications of this directional reflectance for nerve fiber layer measurements in the human eye. METHODS: The retina was modeled as a sphere centered on the optic axis of a schematic eye. Nerve fiber ribbons were projected onto the retina and cylindrical light scattering was calculated along each ribbon. The reflectance along the ribbon was then determined for the illuminating and viewing apertures of two hypothetical optical instruments, a fundus camera and a confocal scanning laser ophthalmoscope. Results were displayed as reflectance maps. RESULTS: Uniformly illuminated nerve fiber ribbons exhibited a nonuniform reflectance pattern that was very sensitive to the location in the pupil of the instrument apertures. Ribbon reflectance at the superior and inferior disc margins varied with ribbon orientation, being higher with temporal tilt and lower with nasal tilt. Ribbons nasal to the disk could be quite dim. CONCLUSIONS: In quantitative nerve fiber layer assessment technologies, the observed reflectance depends on the configuration of the illuminating and viewing apertures of the measuring instrument and on the retinal position and orientation of each nerve fiber bundle. In clinical practice, this dependence may cause significant measurement variability that can be reduced by specific measurement maneuvers.

Fundus Oculi↗
PubMed1982

The accessory optic system in the newt, Triturus cristatus: unitary response properties from the basal optic neuropil.

Recordings from the basal optic neuropil (BON) demonstrated directional sensitivity. These directional sensitivities were different in different units, however, most of them displayed a strong vertical component. Inhibition in the non-preferred direction did not occur, only a lower activation than in the preferred direction was found. The identified velocity functions correlate well with the velocity dependence of the nystagmus frequency demonstrated in the behavior. The units responded well to moving large-area stimuli and exhibited horizontally elongated receptive fields with diameters up to 120 degrees. Additionally, bimodal recordings were observed in the BON which were probably due to input from the otoliths. As the recordings are likely to be presynaptic, the BON receives types of input which establish its function in the control of visuomotor behavior.

Animals↗
PubMedDate not supplied

Fluorescence emission patterns near glass and metal-coated surfaces investigated with back focal plane imaging.

Often fluorophores observed by microscopy are located close to a planar surface as in total internal reflection microscopy or single molecule studies. The optical properties of fluorescence excitation and emission near a planar surface (possibly metal film coated) between two dielectrics are well understood from the viewpoint of classical electromagnetic theory. We present an experimental method whereby the angular dependence of the emission pattern of a fluorophore near a bare surface or a metal film coated surface that supports surface plasmon resonance can be measured with microscope optics. The technique involves an alteration of the microscope optics to directly record (on a digital CCD camera) the intensity pattern at the objective's back focal plane, which directly maps the angular emission pattern of fluorescence. The experimental emission profile on both glass and aluminum-coated surfaces is anisotropic with a peak at either the critical angle or both the critical angle and the surface plasmon angle. The observed profiles agree well with computer calculations and suggest some optical modifications that are potentially useful in cell biophysics.

Coated Materials, Biocompatible↗
PubMed1985

Spatial distribution of visual pigment and dopamine in the bullfrog retina.

Visual pigments and a neurotransmitter, dopamine, were quantitatively investigated in the retina of adult bullfrog, Rana catesbeiana. The adult bullfrog (body length 15-16 cm, body weight 375 +/- 52 g, n = 10) had 21.4 +/- 4.2 nmol visual pigment and 209 +/- 28 pmol dopamine in retinal areas of 266 +/- 27 mm2. Greater pigment densities were recorded in a semicircular band around the optic disc, extending to the nasal and temporal peripheries of the ventral retina. The area with the highest concentration of visual pigment was found in the middle of the dorsal retina, 3-4 mm dorsal to the optic disc. A high concentration of vitamin A2-based pigment was found in the dorsal quarter of the retina (porphyropsin zone); the zone extended up to the most ventral part along peripheral regions of the retina. There was also a band with higher dopamine concentrations although it was not so prominent as that of the visual pigment; the highest concentration of dopamine was found in the area immediately dorsotemporal to the optic disc. Fluorescence micrography indicated that the distribution pattern of catecholamine-containing amacrine cells paralleled that of the dopamine content. The topographic map of dopamine was slightly different from that of visual pigment in the bullfrog retina.

Animals↗
PubMed2002

Vibration maps of capacitive micromachined ultrasonic transducers by laser interferometry.

In this letter, a 1.8-mm x 1.8-mm capacitive micromachined ultrasonic transducer (CMUT) element is experimentally characterized by means of optical measurements. Optical displacement measurements provide information on the resonant behavior of the single membranes and also allow us to investigate the dispersion in the frequency spectrum of adjacent membranes. In addition, higher order mode shapes are observed, showing that either symmetrical or asymmetrical modes are excited in CMUT membranes. Laser interferometry vibration maps, combined with quantitative displacement measurements, provide information about the quality and repeatability of the fabrication process, which is a basic requirement for 2-D array fabrication for ultrasound imaging.

Coated Materials, Biocompatible↗
PubMed2006

A fibre optic scintillator dosemeter for absorbed dose measurements of low-energy X-ray-emitting brachytherapy sources.

A newly developed dosemeter using a 0.5 mm diameter x 0.5 mm thick cylindrical plastic scintillator coupled to the end of a fibre optic cable is capable of measuring the absorbed dose rate in water around low-activity, low-energy X-ray emitters typically used in prostate brachytherapy. Recent tests of this dosemeter showed that it is possible to measure the dose rate as a function of distance in water from 2 to 30 mm of a (103)Pd source of air-kerma strength 3.4 U (1 U = 1 microGy m(2) h(-1)), or 97 MBq (2.6 mCi) apparent activity, with good signal-to-noise ratio. The signal-to-noise ratio is only dependent on the integration time and background subtraction. The detector volume is enclosed in optically opaque, nearly water-equivalent materials so that there is no polar response other than that due to the shape of the scintillator volume chosen, in this case cylindrical. The absorbed dose rate very close to commercial brachytherapy sources can be mapped in an automated water phantom, providing a 3-D dose distribution with sub-millimeter spatial resolution. The sensitive volume of the detector is 0.5 mm from the end of the optically opaque waterproof housing, enabling measurements at very close distances to sources. The sensitive detector electronics allow the measurement of very low dose rates, as exist at centimeter distances from these sources. The detector is also applicable to mapping dose distributions from more complex source geometries such as eye applicators for treating macular degeneration.

Brachytherapy↗
PubMed2006

A feasibility study of optical coherence tomography for guiding deep brain probes.

Deep brain simulation (DBS) is effective for the treatment of various diseases including Parkinson's disease and essential tremor. However, anatomical targeting combined with microelectrode mapping of the region requires significant surgical time. Also, the fine-tipped microelectrode imposes a risk of hemorrhage in the event that the trajectory intersects subcortical vessels. To reduce the operation time and the risk of hemorrhage, we propose to use optical coherence tomography (OCT) to guide the insertion of the DBS probe. We conducted in vitro experiments in the rat brain to study the feasibility of this application. The result shows that OCT is able to differentiate structures in the rat brain. White matter tends to have higher peak reflectivity and steeper attenuation rate compared to gray matter. This structural information may help guide DBS probe advance and electrical measurements.

Animals↗
PubMed1990

X- and Y-mediated current sources in areas 17 and 18 of cat visual cortex.

X- and Y-mediated input to areas 17 and 18 of the cat visual cortex was studied using current-source-density analysis of field potentials evoked by stimulation of the optic nerves. A cuff-shaped electrode was used for stimulation so that Y axons, by virtue of their larger diameters, would have lower electrical thresholds than X axons. The effect in each cortical area of activating Y axons alone could therefore be determined by low-amplitude stimulation of the optic nerves. Current-source densities were calculated by two separate methods. (1) In five experiments, field potentials were measured sequentially at different cortical depths with a single tungsten electrode. Current densities were then calculated by computer. (2) In two experiments, current densities were derived in real time from field potentials recorded simultaneously from three sites with a multi-electrode probe. The calculation was performed by an analog circuit specially designed for this purpose. This method has several advantages over the standard, single-electrode method. At stimulus strengths sufficient to activate the majority of Y axons in the optic nerves, but subthreshold to most X axons, the field potentials evoked in area 17 changed little from layer to layer. When the current-source-density analysis was applied to these potentials, no significant sources or sinks were detectable. Only when the stimulus strength was raised to the point that both X and Y axons were activated by the stimulus were any current sources or sinks detected in area 17. The currents were similar in time course and laminar pattern to those recorded after stimulation of the optic chiasm. In area 18, large sources and sinks were evoked by stimulation of Y axons alone. These currents changed little when the stimulus strength was increased to activate X axons as well. Area 18, therefore, in contrast to area 17, seems to be dominated by Y input and receives little X input. These results support the conclusions of the accompanying paper in which synaptic potentials were recorded intracellularly from cortical neutrons. The intracellular experiments failed to show substantial Y input to area 17. The projections of X and Y axons may therefore be much more highly segregated into areas 17 and 18 than previously thought. Alternatively, the nature of the Y input to area 17 may be very different from that to area 18 in that it cannot be easily detected with intracellular or current-source-density techniques.

Animals↗
PubMed2004

3 dimensional modelling of early human brain development using optical projection tomography.

BACKGROUND: As development proceeds the human embryo attains an ever more complex three dimensional (3D) structure. Analyzing the gene expression patterns that underlie these changes and interpreting their significance depends on identifying the anatomical structures to which they map and following these patterns in developing 3D structures over time. The difficulty of this task greatly increases as more gene expression patterns are added, particularly in organs with complex 3D structures such as the brain. Optical Projection Tomography (OPT) is a new technology which has been developed for rapidly generating digital 3D models of intact specimens. We have assessed the resolution of unstained neuronal structures within a Carnegie Stage (CS)17 OPT model and tested its use as a framework onto which anatomical structures can be defined and gene expression data mapped. RESULTS: Resolution of the OPT models was assessed by comparison of digital sections with physical sections stained, either with haematoxylin and eosin (H&E) or by immunocytochemistry for GAP43 or PAX6, to identify specific anatomical features. Despite the 3D models being of unstained tissue, peripheral nervous system structures from the trigeminal ganglion (approximately 300 microm by approximately 150 microm) to the rootlets of cranial nerve XII (approximately 20 microm in diameter) were clearly identifiable, as were structures in the developing neural tube such as the zona limitans intrathalamica (core is approximately 30 microm thick). Fourteen anatomical domains have been identified and visualised within the CS17 model. Two 3D gene expression domains, known to be defined by Pax6 expression in the mouse, were clearly visible when PAX6 data from 2D sections were mapped to the CS17 model. The feasibility of applying the OPT technology to all stages from CS12 to CS23, which encompasses the major period of organogenesis for the human developing central nervous system, was successfully demonstrated. CONCLUSION: In the CS17 model considerable detail is visible within the developing nervous system at a minimum resolution of approximately 20 microm and 3D anatomical and gene expression domains can be defined and visualised successfully. The OPT models and accompanying technologies for manipulating them provide a powerful approach to visualising and analysing gene expression and morphology during early human brain development.

Brain↗
PubMed2003

Internal structure of the nucleus rotundus revealed by mapping cadherin expression in the embryonic chicken visual system.

The nucleus rotundus is the largest nucleus of the avian thalamus. It is an important center of visual information processing and conveys information from the optic tectum to the ectostriatum in the telencephalon. The nucleus rotundus is generally believed to contain internal divisions processing information on color, form, motion, and looming of visual objects. The detailed arrangement of these internal divisions is unclear. Here, we map the expression of four classic cadherins (N-cadherin, R-cadherin, cadherin-6B, and cadherin-7), which are markers for specific functional gray matter divisions and their fiber connections in the vertebrate brain. Results show that each cadherin is expressed by one coherent part of the nucleus rotundus that is connected to other brain structures by fiber tracts expressing the same subtype of cadherin. Overall, the expression of the four cadherins encompasses almost the entire nucleus rotundus. The four cadherin-expressing parts show different degrees of overlap. For example, the cadherin-6B part and the cadherin-7 part overlap extensively, whereas the R-cadherin part and the cadherin-6B part show little overlap and are partially complementary. Regions with shallow gradients of cadherin expression alternate with regions that show relatively abrupt changes in cadherin expression. At some points, changes of cadherin expression are also arranged in a pinwheel-like fashion, alternating between clockwise and counterclockwise orientations. In general, these results are reminiscent of the organization of functional modules in the mammalian visual cortex. It is speculated that each domain of cadherin expression corresponds to a functional domain, which processes a specific stimulus feature.

Aging↗
PubMed2003

Optical near-field Raman imaging with subdiffraction resolution.

We report optical near-field Raman imaging with subdiffraction resolution (approximately 120 nm) without field enhancement effects. Chemical discrimination on tetracyanoquinodimethane organic thin films showing localized salt complexes is accomplished by detailed Raman maps. Acquisition times that are much shorter than previously reported are due to the high Raman efficiency of the materials and to careful collection and detection of the optical signals in our near-field Raman spectrometer.

Journal Article↗
PubMed1993

Role of the dorsolateral pontine nucleus in two components of optokinetic nystagmus (OKN).

The anatomical features of the dorsolateral pontine nucleus (DLPN) implicate a role of the nucleus in the generation of smooth-pursuit eye movements. The DLPN receives convergent inputs from a variety of parieto-occipital cortical visual areas and projects its fibers to the flocculus and vermal lobules VI and VII. In addition to cortical afferent fibers, the DLPN receives descending fibers from the nucleus of the optic tract which is indicated as the first subcortical optokinetic nystagmus (OKN) relay. DLPN units respond not only to a discrete visual spot but also to large-field OKN stimuli. On the basis of the above anatomical and physiological features, OKN was investigated in 2 alert monkeys whose DLPN was physiologically identified and into which reversible lidocaine was injected. The present findings showed that a rapid rise in OKN velocity was reduced in both monkeys, whose lesions included the uppermost rostral part of the nucleus in the one monkey and the entire nucleus in the other, whereas optokinetic after-nystagmus velocity was affected only in the latter. Taken together with physiological data, the DLPN possibly shares the domain of low selectivity speed selection in OKN and does not play a main role in the generation of OKN.

Animals↗
PubMed2002

Synaptic integration by V1 neurons depends on location within the orientation map.

Neurons in the primary visual cortex (V1) are organized into an orientation map consisting of orientation domains arranged radially around "pinwheel centers" at which the representations of all orientations converge. We have combined optical imaging of intrinsic signals with intracellular recordings to estimate the subthreshold inputs and spike outputs of neurons located near pinwheel centers or in orientation domains. We find that neurons near pinwheel centers have subthreshold responses to all stimulus orientations but spike responses to only a narrow range of orientations. Across the map, the selectivity of inputs covaries with the selectivity of orientations in the local cortical network, while the selectivity of spike outputs does not. Thus, the input-output transformation performed by V1 neurons is powerfully influenced by the local structure of the orientation map.

Action Potentials↗
PubMed1989

Quantitative electrophysiological studies of regenerating visuotopic maps in goldfish--I. Early recovery of dimming sensitivity in tectum and torus longitudinalis.

Refinement and connectivity in the regenerating retinotectal system of goldfish were studied quantitatively by electrophysiological methods. One optic nerve was crushed intraorbitally in fish kept at 25 degrees C. At different postcrush times, visually-evoked multiunit activity was recorded from the superficial layers of tectum, and from the torus longitudinalis. Responses in torus longitudinalis were used as a test of retinotectal connectivity because torus longitudinalis derives a visuotopic map from a tectal projection. The stimulus, effective for both the early retinotectal projection and torus longitudinalis, was a 10 degrees wide vertical black stripe rotated horizontally at 25 degrees/s through both visual fields. Activity from repeated sweeps was averaged to yield receptive field profiles in the horizontal dimension. Normally, profiles from tectum were dual-peaked and 20 degrees wide at half maximum amplitude; torus longitudinalis profiles were bell-shaped and 41 degrees wide. Between 20 and 40 days postcrush, tectum gave broad low-amplitude (25% normal) profiles that were roughly visuotopic. Over the same period, torus longitudinalis gave profiles of relatively high amplitude (69% of normal) that were also broadened but normally visuotopic. The widths of both tectal and torus longitudinalis profiles declined with the same exponential timecourse, reaching normal values by 80-100 days. Torus longitudinalis profiles were on average 21.6 degrees wider than tectal profiles at all stages of regeneration. The results agree with previous anatomical observations showing that optic fibers initially form much enlarged arbors that shrink over time, and suggest that arbors engage in widespread synaptic connections, at least with tecto-torus longitudinalis cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed2000

Noninvasive functional imaging of human brain using light.

Analysis of photon transit time for low-power light passing into the head, and through both skull and brain, of human subjects allowed for tomographic imaging of cerebral hemoglobin oxygenation based on photon diffusion theory. In healthy adults, imaging of changes in hemoglobin saturation during hand movement revealed focal, contralateral increases in motor cortex oxygenation with spatial agreement to activation maps determined by functional magnetic resonance imaging; in ill neonates, imaging of hemoglobin saturation revealed focal regions of low oxygenation after acute stroke, with spatial overlap to injury location determined by computed tomography scan. Because such slow optical changes occur over seconds and co-localize with magnetic resonance imaging vascular signals whereas fast activation-related optical changes occur over milliseconds and co-localize with EEG electrical signals, optical methods offer a single modality for exploring the spatio-temporal relationship between electrical and vascular responses in the brain in vivo, as well as for mapping cortical activation and oxygenation at the bedside in real-time for clinical monitoring.

Adult↗
PubMed2003

Reorganization of visual cortical maps after focal ischemic lesions.

Plasticity after central lesions may result in the reorganization of cortical representations of the sensory input. Visual cortex reorganization has been extensively studied after peripheral (retinal) lesions, but focal cortical lesions have received less attention. In this study, we investigated the organization of retinotopic and orientation preference maps at different time points after a focal ischemic lesion in the primary visual cortex (V1). We induced a focal photochemical lesion in V1 of kittens and assessed, through optical imaging of intrinsic signals, the functional cortical layout immediately afterwards and at 4, 13, 33, and 40 days after lesion. We analyzed histologic sections and evaluated temporal changes of functional maps. Histological analysis showed a clear lesion at all time points, which shrank over time. Imaging results showed that the retinotopic and orientation preference maps reorganize to some extent after the lesion. Near the lesion, the cortical retinotopic representation of one degree of visual space expands over time, while at the same time the area of some orientation domains also increases. These results show that different cortical representations can reorganize after a lesion process and suggest a mechanism through which filling-in of a cortical scotoma can occur in cortically damaged patients.

Animals↗