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At least 1,207 records · Page 67Linked to original sources
PubMed2006

Analysis of the resolution-bandwidth-noise trade-off in wavelength-based photonic analog-to-digital converters.

The performance of wavelength-based photonic analog-to-digital converters (ADCs) is theoretically analyzed in terms of resolution and bandwidth as well as of noise tolerance. The analysis applies to any photonic ADC in which the analog input signal is converted into the wavelength of an optical carrier, but special emphasis is put on the spectrometerlike setup in which the wavelength is mapped to a spatial spot position. The binary output signals are then retrieved by an array of fan-out diffractive optical elements that redirect the beam onto the correct detectors. In particular, the case when the input signal controls the wavelength directly such that it will chirp in frequency during each sampling pulse or interval is studied. This chirping obviously broadens the spot on the diffractive optical element array; the effect of this broadening on noise tolerance and comparator accuracy is analytically analyzed, and accurate numerical calculations of the probability of error are presented.

Journal Article↗
PubMed2002

Intrinsic optical signals from rat primary auditory cortex in response to sound stimuli presented to contralateral, ipsilateral and bilateral ears.

In the auditory cortex, primitive features of acoustic stimuli are represented for auditory scene analysis. A typical example of a feature representation is the tonotopic map, in which sound frequencies are spatially arranged in an orderly manner. Some neurons in the auditory cortex are sensitive to sound source location, which is another important feature for auditory scene analysis. In the present study, using the intrinsic optical imaging technique, we attempted to visualize the two-dimensional pattern of neuronal population responses in the primary auditory cortex of rats to pure tones presented at various frequencies and sound intensities. The observed arrangements of sound frequencies were consistent with those obtained by electrophysiological mapping, which indicates that our intrinsic optical recording can visualize populational responses of neurons. We also found different temporal patterns of intrinsic signals elicited in response to contralateral, ipsilateral, and bilateral ear stimulations. Finally we try to explain the observed differential time courses of intrinsic signal responses from the theoretical point of view on the conduction of neural activities, based on the so far anatomically identified neural pathways in the rodent auditory system.

Acoustic Stimulation↗
PubMed2006

SPR-based immunocapture approach to creating an interfacial sensing architecture: Mapping of the MRS18-2 binding site on retinoblastoma protein.

Biosensor technologies based on optical readout are widely used in protein-protein interaction studies. Here we describe a fast and simple approach to the creation of oriented interfacial architectures for surface plasmon resonance (SPR) transducers, based on conventional biochemical procedures and custom reagents. The proposed protocol permits the oriented affinity-capture of GST fusion proteins by a specific antibody which is bound to protein A, which in turn has been immobilized on the transducer surface (after the surface has been modified by guanidine thiocyanate). The applicability of the method was demonstrated by studying the interaction between retinoblastoma tumor suppressor protein (pRb) and MRS18-2 proteins. The formation of the pRb-MRS18-2 protein complex was examined and the pRb binding site (A-box-spacer-B-box) was mapped. We have also shown that MRS18-2, which was detected as the Epstein-Barr virus-encoded EBNA-6 binding partner using the yeast two-hybrid system, binds to pRb in GST pull-down assays.

Antibodies↗
PubMed2003

Independence of visuotopic representation and orientation map in the visual cortex of the cat.

The representations of visual space and stimulus orientation were mapped in the cat primary visual cortex using electrophysiological recordings supplemented with intrinsic signal optical imaging. The majority of units displaced up to 600 micro m laterally had overlapping RFs both in orientation domains and around singularities of the orientation map. Quantitative comparison of these units revealed only a weak, positive correlation between the difference in their preferred orientations and RF separations (area 17: r = 0.09; area 18: r = 0.15). The occurrence of nonoverlapping RFs could be accounted for by random RF position scatter rather than by orientation difference between the units. Monte Carlo analysis showed that our findings are compatible with a locally smooth and linear representation of visual space that is not coupled to the representation of stimulus orientation. An important functional implication of the above map relationships is that positional information captured by the retina is faithfully transmitted into the cortex.

Animals↗
PubMed2004

Columnar specificity of microvascular oxygenation and volume responses: implications for functional brain mapping.

Cortical neurons with similar properties are grouped in columnar structures and supplied by matching vascular networks. The hemodynamic response to neuronal activation, however, is not well described on a fine spatial scale. We investigated the spatiotemporal characteristics of microvascular responses to neuronal activation in rat barrel cortex using optical intrinsic signal imaging and spectroscopy. Imaging was performed at 570 nm to provide functional maps of cerebral blood volume (CBV) changes and at 610 nm to estimate oxygenation changes. To emphasize parenchymal rather than large vessel contributions to the functional hemodynamic responses, we developed an ANOVA-based statistical analysis technique. Perfusion-based maps were compared with underlying neuroanatomy with cytochrome oxidase staining. Statistically determined CBV responses localized accurately to individually stimulated barrel columns and could resolve neighboring columns with a resolution better than 400 microm. Both CBV and early oxygenation responses extended beyond anatomical boundaries of single columns, but this vascular point spread did not preclude spatial specificity. These results indicate that microvascular flow control structures providing targeted flow increases to metabolically active neuronal columns also produce finely localized changes in CBV. This spatial specificity, along with the high contrast/noise ratio, makes the CBV response an attractive mapping signal. We also found that functional oxygenation changes can achieve submillimeter specificity not only during the transient deoxygenation ("initial dip") but also during the early part of the hyperoxygenation. We, therefore, suggest that to optimize hemodynamic spatial specificity, appropriate response timing (using < or =2-3 sec changes) is more important than etiology (oxygenation or volume).

Animals↗
PubMed1978

Anatomical mapping of retino-tectal connections in developing and metamorphosed Xenopus: evidence for changing connections.

Neural connections between the eye and optic tectum in Xenopus laevis were anatomically traced by observing the tectal location of Wallerian degeneration after discrete retinal lesion. These retinotectal connections were mapped in postmetamorphic frogs and tadpoles at stage 51, the stage at which retinal axons have grown into about the rostral one-half of the tectum. The course of the experimental degeneration was the same in frogs and tadpoles, but degeneration proceeded faster in the younger animals. In the frogs, connections were ordered, with nasal retina mapping to the caudal part of the tectum and temporal retina mapping to the rostral tectum. In the tadpoles, within the innervated area at the rostral tectum, the retino-tectal connections were generally organized as in the adults, with the temporal retina mapping to the rostral part of the innervated tectum and nasal retina mapping primarily to the caudal part. But a portion of the nasal fibers consistently mapped to the far rostral tectum as well. Electron microscopic observations showed degenerating synaptic terminals at both rostral and caudal portions of the innervated tectum after lesion of just the nasal retina. Degeneration was not seen in control animals. These results indicate that some fibers (particularly from nasal retina) may shift their terminals caudally on the tectum to match tectal growth and produce the adult pattern of connections. If there is such connection readjustment, the 'aberrant' connections from nasal retina in tadpoles may be an indication of this process.

Animals↗
PubMed2004

Optical imaging of binaural interaction in multiple fields of the guinea pig auditory cortex.

Locating the source of a sound is an important function of the auditory system and interaural intensity differences are one of the most important cues. To study the functional pathways of sound localisation processing in the auditory cortex, activity in multiple fields of the guinea pig auditory cortex during stimulation with interaural intensity differences was studied using optical imaging with a voltage-sensitive dye. Of the auditory core (primary and dorsocaudal) and the belt fields which surround them, the posterior and ventroposterior belt fields were the most sensitive to interaural intensity differences. This suggests that the caudal pathway of the auditory cortex is involved in sound localisation.

Acoustic Stimulation↗
PubMed1969

Control of body temperature in the unanaesthetized monkey by cholinergic and aminergic systems in the hypothalamus.

1. In the unanaesthetized rhesus monkey, 5-hydroxytryptamine (5-HT), catecholamines, acetylcholine or carbachol were micro-injected in a volume of 1.0 mul. or less through chronically implanted cannulae at eighty-six sites in the hypothalamus.2. 5-HT in doses of 2-10 mug caused a long-lasting elevation in temperature which was dose-dependent. An anatomical ;mapping' of the hypothalamus revealed that the hyperthermic action of 5-HT was localized to the anterior, pre-optic area directly ventral to the anterior commissure.3. Noradrenaline in doses of 1-12 mug produced a dose-dependent fall in temperature of short duration. An anatomical ;mapping' showed that the hypothermic action of this and other catecholamines was again localized to the anterior, pre-optic region.4. Acetylcholine, alone or in a mixture with eserine, or carbachol caused a dose-dependent hyperthermia which was characterized by an intense rise of short duration and vigorous shivering. A ;mapping' of this response revealed a diffuse patterning of sites throughout the hypothalamus which were sensitive to the application of acetylcholine and carbachol. However, in one circumscribed region at the junction between the posterior hypothalamus and mesencephalon, the two cholinomimetic substances caused a marked fall in temperature.5. We conclude that 5-HT activates a cholinergic heat production pathway which projects from the anterior to posterior hypothalamus. Noradrenaline, on the other hand, blocks the hyperthermic action of 5-HT rather than activates the heat loss system. A chemically mediated heat loss pathway apparently does not exist in the hypothalamus.

Acetylcholine↗
PubMed2005

Boundary cue invariance in cortical orientation maps.

We effortlessly perceive oriented boundaries defined by either luminance changes ('first-order' cues) or texture variations ('second-order' cues). Many neurons in mammalian visual cortex show orientation preference to both types of boundaries, but it is uncertain how they contribute to perceptual orientation cue-invariance at the neuronal population level. Using optical imaging in cat A 18, we observed highly similar orientation preference maps to first-order and a variety of second-order visual stimuli. Thus the neuronal representation of coarse-scale boundary orientation appears to be invariant to the characteristics (including local orientation) of the fine-scale textures by which those boundaries are defined. A common feature of second-order visual stimuli is that modulation shifts their Fourier energy for boundary orientation to the higher spatial frequencies of their constituent textures - our results suggest a common neural mechanism (demodulation) mediating visual processing of many kinds of texture boundary. The similarity between orientation maps to different stimuli implies that second-order responsive neurons are homogeneously distributed across the cortical surface. Such homogeneously cue-invariant orientation representation could provide a neural substrate for perceptual form-cue invariance, and reflect an optimal organization for encoding orientation information in natural scenes.

Animals↗
PubMed1995

Topographic determination of corneal asphericity and its lack of effect on the refractive outcome of radial keratotomy.

PURPOSE: The normal human cornea flattens peripherally. The amount of flattening, or asphericity, has traditionally been calculated from multiple keratometric measurements. We devised a mathematical technique for determining asphericity from computed corneal topography. We then determined whether asphericity affects the refractive outcome of radial keratotomy. METHODS: One eye each of 41 patients who underwent four- or eight-incision radial keratotomy and preoperative computed corneal topography was identified retrospectively and analyzed. The asphericity, P, of each cornea was calculated by fitting Baker's equation (y2 = 2r0x-Px2) to each meridian of the topographic map. For each patient, we calculated the difference between the refractive outcome in diopters for radial keratotomy and the prediction of a quadratic least-squares best-fit model involving optical zone size and age. RESULTS: Aspericity could be calculated from the topographic maps in all 41 patients and ranged from 0.33 to 1.28, with mean +/- S.D. of 0.82 +/- 0.21. Aphericity varied among the meridians of a cornea, with an average standard deviation among meridians of 0.17. No statistical correlation was found between calculated asphericity and refractive outcome. CONCLUSIONS: Corneal asphericity can be calculated from corneal topographic maps. Asphericity is not constant in the different meridians of a normal cornea. Corneal asphericity is not useful in predicting the refractive outcome of radial keratotomy.

Adult↗
PubMed2000

Human cortical areas underlying the perception of optic flow: brain imaging studies.

In summary, we have reviewed electrophysiological and brain imaging studies of motion and optic-flow processing. Single-unit studies indicate that MST (V5a) is a site of optic-flow extraction and that this information can be used to guide pursuit eye movements and to estimate heading. The EEG and MEG studies point to a localized electrical dipole in occipitotemporal cortex evoked by visual motion. We have also discussed the evidence from functional imaging studies for response specificity of the rCBF and BOLD effects in posterior cortex to visual motion and optic flow. Focal attention modulates the amplitude of the BOLD signal evoked by visual motion stimulation. Retinotopic mapping techniques have been used to locate region borders within the visual cortex. Our results indicate that striate (V1) and extrastriate areas (V2, V3/V3a) respond robustly to optic flow. However, with exception of a more pronounced response in V3/V3a to random walk, we found little evidence for response selectivity with respect to flow type and disparity in these early visual areas. In a similar fashion, the human V5/V5a complex responds well to optic flow, but these responses do not vary significantly with the type of flow field and do not seem to depend on disparity. In contrast, the kinetic occipital area (KO/V3b) responds well to optic-flow information, and it is the only area that produces more pronounced activation to the disparity in the flow fields. These initial results are promising because they suggest that the fMRI method can be sensitive to changes in stimulus parameters that define flow fields. More work will be required to explore the extent to which these responses reflect the neuronal processing of optic flow. Eye position tracking is now possible during fMRI experiments. We have demonstrated that the eye movements affect the BOLD responses in motion-sensitive areas (Kimming et al., 1999). Further experiments in our laboratory are aimed at understanding the effects of eye movements on the neuronal coding of complex optic-flow fields (Schira et al., 1999).

Animals↗
PubMed1993

Two stages in the development of a mammalian retinocollicular projection.

The retinocollicular projection in the marsupial mammal the wallaby Macropus eugenii, has been investigated anatomically to determine the order in the developing projection and electrophysiologically to determine the time of onset of synaptic transmission by recording evoked potentials in the colliculus in response to stimulation of the optic nerve. There are two clear stages: a protracted period when retinal axons grow into the colliculus in coarse retinotopic order with no recordable electrical activity followed by the formation of terminal zones in retinotopically correct positions, the loss of more widely distributed axons and the onset of evoked potentials. The two stages are not seen in non-mammalian vertebrates where the projection is functional from the beginning.

Animals↗
PubMed1988

Projections of the dorsal and lateral terminal accessory optic nuclei and of the interstitial nucleus of the superior fasciculus (posterior fibers) in the rabbit and rat.

The projections of the dorsal and lateral terminal accessory optic nuclei (DTN and LTN) and of the dorsal and ventral components of the interstitial nucleus of the superior fasciculus (posterior fibers; inSFp have been studied in the rabbit and rat by the method of retrograde axonal transport following injections of horseradish peroxidase into oculomotor-related brainstem nuclei. The projections of the ventral division of the inSFp have been further investigated in rabbits with the anterograde axonal transport of 3H-leucine. The data show that the projections of the DTN, LTN, and inSFp are remarkably similar in rabbit and rat. The DTN projects heavily to the ipsilateral medial terminal accessory optic nucleus (MTN), nucleus of the optic tract, and dorsal cap of the inferior olive. The DTN projects sparsely to the ipsilateral visual tegmental relay zone and to the contralateral superior and lateral vestibular nuclei. The LTN and dorsal component of the inSFp are found to share the same basic connections; both project heavily to the ipsilateral nucleus of the optic tract and visual tegmental relay zone and send a moderately sized projection to the ipsilateral MTN. However, while the dorsal component of the inSFp sends significant ipsilateral projections to both rostral and caudal portions of the dorsal cap, only a few LTN neurons appear to follow this example and only by projecting to the rostral part of the dorsal cap. In addition, both the LTN and dorsal component of the inSFp send sparse contralateral projections to the MTN, nucleus of the optic tract, and visual tegmental relay zone; and the dorsal component of the inSFp also provides a sparse contralateral projection to both rostral and caudal portions of the dorsal cap. The ventral component of the inSFp projects heavily to the ipsilateral visual tegmental relay zone and moderately to the ipsilateral MTN and nucleus of the optic tract. The ventral inSFp projects sparsely to the contralateral MTN, the nucleus of the optic tract, and the visual tegmental relay zone. A few of its neurons target the ipsilateral dorsal cap of the inferior olive. Unlike the DTN (present study) and the MTN (Giolli et al.: J. Comp. Neurol. 227:228-251, '84; J. Comp. Neurol. 232:99-116, '85a), the LTN and the inSFp of the rabbit and rat lack projections to the superior and lateral vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

X-ray microCT study of pyramids of the sea urchin Lytechinus variegatus.

This paper reports results of a novel approach, X-ray microCT, for quantifying stereom structures applied to ossicles of the sea urchin Lytechinus variegatus. MicroCT, a high resolution variant of medical CT (computed tomography), allows noninvasive mapping of microstructure in 3-D with spatial resolution approaching that of optical microscopy. An intact pyramid (two demipyramids, tooth epiphyses, and one tooth) was reconstructed with 17 microm isotropic voxels (volume elements); two individual demipyramids and a pair of epiphyses were studied with 9-13 microm isotropic voxels. The cross-sectional maps of a linear attenuation coefficient produced by the reconstruction algorithm showed that the structure of the ossicles was quite heterogeneous on the scale of tens to hundreds of micrometers. Variations in magnesium content and in minor elemental constitutents could not account for the observed heterogeneities. Spatial resolution was insufficient to resolve the individual elements of the stereom, but the observed values of the linear attenuation coefficient (for the 26 keV effective X-ray energy, a maximum of 7.4 cm(-1) and a minimum of approximately 2 cm(-1) away from obvious voids) could be interpreted in terms of fractions of voxels occupied by mineral (high magnesium calcite). The average volume fraction of mineral determined for a transverse slice of the demipyramid near where it joins an epiphysis was 0.46; for a slice 3.3 mm adoral it was 0.70. Local volume fractions of mineral approached 1, and, away from resolvable voids, considerable portions of the demipyramids had volume fractions of calcite at or below approximately 0.33. MicroCT imaging of a demipyramid before and after infiltration with a high absorptivity fluid (sodium polytungstate) confirmed the determination of the volume fractions of minerals.

Animals↗
PubMed1993

Visually guided reaching with the forelimb contralateral to a "blind" hemisphere: a metabolic mapping study in monkeys.

The 2-14C-deoxyglucose method was used to map local cerebral metabolic activity in monkeys performing a unimanual task requiring visually guided arm reaching and key pressing. The study was carried out with monkeys that either had intact brains or had one hemisphere deprived of visual input by unilateral optic tract section combined in some cases with forebrain commissurotomy. The metabolic mapping revealed activation of sensorimotor cortex only in the hemisphere contralateral to the moving forelimb, irrespective of whether this hemisphere was intact or visually deafferented. These results suggest that visually guided reaching with the forelimb contralateral to the "blind" hemisphere is subserved by that hemisphere's sensorimotor cortex and not by the cortex of the ipsilateral, "seeing" hemisphere. Other areas that were more active metabolically in the "blind" than in the "seeing" hemisphere included the supplementary motor, the secondary somatosensory, and certain posterior parietal cortical areas, intraparietal lateral 5 (lateral 5-ip), 7a, and intraparietal 7 (7-ip). It is suggested that the "blind" hemisphere utilizes at least two distinct pieces of information to guide forelimb movements to visual targets: (1) information about the location of the visual target derived from head and eye movements made to this target and mediated via the inferior parietal cortical areas 7a and 7-ip, and (2) information about the instantaneous upper extremity position derived from forelimb proprioceptive mechanisms and mediated via the somatosensory cortex and thereafter via the superior parietal cortical area, lateral 5-ip.

Animals↗
PubMed1988

An optic-fiber photocell detector for measuring tongue protrusion in the rat: evaluation of recovery from localized cortical lesions.

A technique for measuring tongue protrusion during licking by rats is described. Liquid is automatically dispensed onto a shelf in front of the rats' cage. An array of 16 optic fibers spaced at 1 mm intervals act as photo detectors to measure tongue protrusion. The fibers activate relays connected to a microcomputer that counts individual beam breaks. The system permits the measurement of large numbers of consecutive tongue protrusions during training and testing of control and brain-damaged rats. It is shown that ventral frontal cortical lesions disrupt tongue protrusion more severely than posterior neocortex removal or dorsal frontal ablations. Complete frontal cortex lesions permit no sparing or recovery of tongue protrusion.

Animals↗
PubMed2004

Doppler optical coherence imaging of converging flow.

The experimental methods of Doppler optical coherence tomography are applied for two-dimensional flow mapping of highly scattering fluid in flow with complex geometry. Converging flow (die entry) is used to demonstrate non-invasive methods to map varying velocity profiles before and after the entry. Complex geometry flow is scanned with approximately 10 x 10 x 10 microm3 spatial resolution. Structural images of the phantom and specific velocity images are demonstrated. A variety of velocity profiles have been obtained before and after the entry. Concave, blunted, parabolic and triangular profiles are obtained at different distances after the entry. Application of the technique to the study of blood circulation is discussed.

Blood Flow Velocity↗