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Results for “Optical mapping”

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At least 973 records · Page 54Linked to original sources
PubMed2004

A temporal study of axonal degeneration and glial scar formation following a standardized crush injury of the optic nerve in the adult rat.

PURPOSE: In this methodological study, we describe a standardized optic nerve injury model in adult rats. The temporal pattern of the glial response is mapped in relation to axonal regeneration and degeneration. METHODS: A standardized optic nerve crush injury was made in adult rats, using a fine pair of forceps with a preset pressure of 0.6 N during 10 seconds. RESULTS: This crush injury resulted in a pronounced astroglial and microglial proliferation 2-7 dpi. Degenerative axons distal to the lesion presented a gradual decrease in neurofilament immunoreactivity. In contrast, Fluoro-Jade staining was gradually increased in these degenerative axons from 2-7 dpi. Regeneration was observed proximal to the lesion in sprouts double labeled with the tracer Fluoro-Gold and anti-GAP43. CONCLUSION: The standardized optic nerve crush injury model used in the present study resulted in a reproducible degenerative pattern including a pronounced astroglial and microglial proliferation. The gradual decrease in Neurofilament immunoreactivity in degenerative axons, and a gradual increase in Fluoro-Jade staining was paralleled with a spontaneous regeneration proximal to the lesion, shown with tracing and GAP43-immunoreactivity. The combination of these markers and this experimental setup thus allows analysis of the entire degenerative/regenerative process in a standardized CNS axotomy model.

Animals↗
PubMed2004

Changes in serial optical topography and TMS during task performance after constraint-induced movement therapy in stroke: a case study.

The authors examined serial changes in optical topography in a stroke patient performing a functional task, as well as clinical and physiologic measures while undergoing constraint-induced therapy (CIT). A 73-year-old right hemiparetic patient, who had a subcortical stroke 4 months previously, received 2 weeks of CIT. During the therapy, daily optical topography imaging using near-infrared light was measured serially while the participant performed a functional key-turning task. Clinical outcome measures included the Wolf Motor Function Test (WMFT), Motor Activity Log (MAL), and functional key grip test. Transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) were also used to map cortical areas and hemodynamic brain responses, respectively. Optical topography measurement showed an overall decrease in oxy-hemoglobin concentration in both hemispheres as therapy progressed and the laterality index increased toward the contralateral hemisphere. An increased TMS motor map area was observed in the contralateral cortex following treatment. Posttreatment fMRI showed bilateral primary motor cortex activation, although slightly greater in the contralateral hemisphere, during affected hand movement. Clinical scores revealed marked improvement in functional activities. In one patient who suffered a stroke, 2 weeks of CIT led to improved function and cortical reorganization in the hemisphere contralateral to the affected hand.

Aged↗
PubMed2002

Non-invasive assessment of language lateralization by transcranial near infrared optical topography and functional MRI.

Near infrared optical topography (OT) is the simultaneous acquisition of hemoglobin absorption from an array of optical fibers on the scalp to construct maps of cortical activity. We demonstrate that OT can be used to determine lateralization of prefrontal areas to a language task that has been validated by functional MRI (fMRI). Studies were performed on six subjects using a visually presented language task. Laterality was quantified by the relative number of activated pixels in each hemisphere for fMRI, and the total hemoglobin responses in each hemisphere for OT. All subjects showed varying degrees of left hemisphere language dominance and the mean laterality indices for subjects who underwent both OT and fMRI were in good agreement. These studies demonstrate that OT gives predictions of hemispheric dominance that are consistent with fMRI. Due to the ease of use and portable nature of OT, it is anticipated that optical topography will be valuable tool for neurological examinations of cognitive function.

Adult↗
PubMed2006

Three-dimensional optic axis determination using variable-incidence-angle polarization-optical coherence tomography.

Polarization optical coherence tomography (PSOCT) is a powerful technique to nondestructively map the retardance and fast-axis orientation of birefringent biological tissues. Previous studies have concentrated on the case where the optic axis lies on the plane of the surface. We describe a method to determine the polar angle of the optic axis of a uniaxial birefringent tissue by making PSOCT measurements with a number of incident illumination directions. The method is validated on equine flexor tendon, yielding a variability of 4% for the true birefringence and 3% for the polar angle. We use the method to map the polar angle of fibers in the transitional region of equine cartilage.

Animals↗
PubMed1997

Near-simultaneous hemoglobin saturation and oxygen tension maps in mouse brain using an AOTF microscope.

A newly developed microscope using acousto-optic tunable filters (AOTFs) was used to generate in vivo hemoglobin saturation (SO2) and oxygen tension (PO2) maps in the cerebral cortex of mice. SO2 maps were generated from the spectral analysis of reflected absorbance images collected at different wavelengths, and PO2 maps were generated from the phosphorescence lifetimes of an injected palladium-porphyrin compound using a frequency-domain measurement. As the inspiratory O2 was stepped from hypoxia (10% O2), through normoxia (21% O2), to hyperoxia (60% O2), measured SO2 and PO2 levels rose accordingly and predictably throughout. A plot of SO2 versus PO2 in different arterial and venous regions of the pial vessels conformed to the sigmoidal shape of the oxygen-hemoglobin dissociation curve, providing further validation of the two mapping procedures. The study demonstrates the versatility of the AOTF microscope for in vivo physiologic investigation, allowing for the generation of nearly simultaneous SO2 and PO2 maps in the cerebral cortex, and the frequency-domain detection of phosphorescence lifetimes. This class of study opens up exciting new possibilities for investigating the dynamics of hemoglobin and O2 binding during functional activation of neuronal tissues.

Acoustics↗
PubMed1993

Sound-localization deficits induced by lesions in the barn owl's auditory space map.

Barn owls possess a two-dimensional map of auditory space. The map appears in its final form in the external nucleus of the inferior colliculus (ICx) and is projected from there to the optic tectum (OT). To determine the role of the map in ICx or its projected version in OT in the localization of acoustic stimuli, head movements of three adult owls were recorded before and after lesioning parts of the map either in ICx or in OT. Small electrolytic lesions caused sound-localization deficits that were characterized by failures to turn, turns away from the sound source, increased response latencies, and reduced turning amplitudes. These deficits occurred at azimuths expected from the physiological data obtained at the lesion site before passing current. They extended over an azimuthal range of some 20 degrees. Thus, this is the first unambiguous demonstration, for sound localization, of a deficit covering a well circumscribed area within an auditory hemifield. Since the major lesion deficits were restricted to one hemifield, a second lesion was made in the space map of the other side of the brain in each animal. The second lesion resulted in behavioral deficits qualitatively similar to those produced by the first lesion. In total, the study is based on nine lesions, three in each owl. Two lesions were sham lesions. These and two further lesions did not produce a measurable deficit. In four of the five remaining cases, in which a behavioral deficit was observed initially, the behavioral performance recovered with time. In two cases, the deficit disappeared completely. Although improvement occurred also in the remaining two cases, prelesion response amplitudes were not reached in one case, and response latency did not reach prelesion values in the other case. Because the behavioral deficits induced by the second lesions disappeared in the same way as did the deficits induced by the first lesions, the possibility is excluded that the animals learned to respond tactically, that is, that they learned to associate "unlocatable sounds" with the lesioned side. The deficits were also not due to a generalized motor impairment, because immediately after the lesion the animals responded as they did before the lesion to stimulation from outside the well circumscribed affected region of space. The possibility is discussed that plasticity after small central (neural) injuries is maintained longer in the lifetime of an animal than plasticity after peripheral (mechanical) manipulations.

Animals↗
PubMed2001

Mapping the distribution of emissive molecules in human ocular lipofuscin granules with near-field scanning optical microscopy.

Several high resolution imaging techniques are utilized to probe the structure of human ocular lipofuscin granules. Atomic force microscopy reveals typical granule sizes to be about one micrometre in diameter and hundreds of nanometres in height, in agreement with previous electron microscopy results. For issues concerning the role of lipofuscin in age-related macular degeneration, recent attention has focused on the orange-emitting fluorophore, A2E. Confocal microscopy measurements are presented which reveal the presence of a highly emissive component in the granules, consistent with the presence of A2E. It is shown, however, that the interpretation of these results is complicated by the lack of structural details about the particles. To address these issues, near-field scanning optical microscopy (NSOM) measurements are presented which measure both the lipofuscin fluorescence and topography, simultaneously. These measurements reveal distinct structure in the fluorescence image which do not necessarily correlate with the topography of the granules. Moreover, direct comparison between the NSOM fluorescence and topography measurements suggests that A2E is not the major component in lipofuscin. These measurements illustrate the unique capabilities of NSOM for probing into the microstructure of lipofuscin and uncovering new insights into its phototoxicity.

Aged↗
PubMed2003

Quantifying Doppler angle and mapping flow velocity by a combination of Doppler-shift and Doppler-bandwidth measurements in optical Doppler tomography.

Recently we introduced a novel procedure that estimates Doppler angle and flow velocity simultaneously by combining Doppler-shift and Doppler-bandwidth measurements with a conventional single-beam optical Doppler tomography device. Here we validate this method experimentally with two Intralipid flow setups that correspond to fixed Doppler angle and fixed flow speed. One set of data has a fixed flow speed of 53.6 mm/s with a Doppler angle that changes from 56 degrees to 90 degrees; the other has a fixed Doppler angle of 80 degrees with flow speed that changes from 18.5 to 141.9 mm/s. As obtained with the method introduced here, the Doppler-angle estimation accuracies of the two sets are 97.6% and 98.2%, respectively, and the estimation accuracies of flow speeds of the two sets are 94.3% and 90.4%, respectively.

Algorithms↗
PubMed2000

Schwann cells in the regenerating fish optic nerve: evidence that CNS axons, not the glia, determine when myelin formation begins.

Fish optic nerve fibres quickly regenerate after injury, but the onset of remyelination is delayed until they reach the brain. This recapitulates the timetable of CNS myelinogenesis during development in vertebrate animals generally, and we have used the regenerating fish optic nerve to obtain evidence that it is the axons, not the myelinating glial cells, that determine when myelin formation begins. In fish, the site of an optic nerve injury becomes remyelinated by ectopic Schwann cells of unknown origin. We allowed these cells to become established and then used them as reporters to indicate the time course of pro-myelin signalling during a further round of axonal outgrowth following a second upstream lesion. Unlike in the mammalian PNS, the ectopic Schwann cells failed to respond to axotomy and to the initial outgrowth of new optic axons. They only began to divide after the axons had reached the brain. Shortly afterwards, small numbers of Schwann cells began to leave the dividing pool and form myelin sheaths. More followed gradually, so that by 3 months remyelination was almost completed and few dividing cells were left. Moreover, remyelination occurred synchronously throughout the optic nerve, with the same time course in the pre-existing Schwann cells, the new ones that colonised the second injury, and the CNS oligodendrocytes elsewhere. The optic axons are the only common structures that could synchronise myelin formation in these disparate glial populations. The responses of the ectopic Schwann cells suggest that they are controlled by the regenerating optic axons in two consecutive steps. First, they begin to proliferate when the growing axons reach the brain. Second, they leave the cell cycle to differentiate individually at widely different times during the ensuing 2 months, during the critical period when the initial rough pattern of axon terminals in the optic tectum becomes refined into an accurate map. We suggest that each axon signals individually for myelin ensheathment once it completes this process.

Animals↗
PubMed2000

Homozygosity mapping of spinocerebellar ataxia with cerebellar atrophy and peripheral neuropathy to 9q33-34, and with hearing impairment and optic atrophy to 6p21-23.

With the availability of a simple molecular test that distinguishes Friedreich ataxia, the most frequent form of inherited ataxia, from other recessive ataxias, it now becomes possible to unravel the genetic heterogeneity of the latter. We have now localised two genes causing autosomal recessive spinocerebellar ataxia in two consanguineous families. In the first family, the four affected Japanese sibs had spinocerebellar ataxia associated with elevated levels of serum creatine kinase, gamma-globulin, and alpha-foetoprotein. Homozygosity over a 20 cM region allowed to demonstrate linkage at 9q33.3-34.3 with a lod score of 3.0. Genotyping two unrelated Japanese patients from first degree consanguineous parents revealed that one was homozygous for the same region but did not share the biochemical features. In the second family, an Israeli uncle and a niece were affected by an early-onset recessive ataxia and subsequently developed hearing impairment and optic atrophy. Homozygosity over a 17 cM region allowed demonstration of linkage at 6p21-23 with a lod score of 3.25. These two localisations of autosomal recessive ataxia genes represent a first step toward the identification of genetically homogenous, non-Friedreich, ataxic patients and subsequent cloning of the genes.

Chromosome Mapping↗
PubMed2000

Pseudo-random procedures for rapid presentation rates using optical imaging and spectroscopy.

Optical imaging of rat barrel cortex has provided detailed spatio-temporal maps of functional cortical architecture. We describe an event-related procedure (ERP) for optical imaging based on selective signal averaging as reported by Burock et al., using an anti-correlative pseudo-random event sequence. The sequence used 1 s vibrissal stimulation at 5 Hz, with an interevent interval of 2 s. This rapid presentation rate allows for greater statistical power per unit time, and allows for direct comparison of event-related studies with other imaging modalities. The spatio-temporal characteristics of single wavelength and spectrographic results were found to be comparable with those obtained by standard techniques, although a general lessening of haemodynamic response function (HRF) was noted. We also describe a method of locating barrel activity by spectral analysis of summed event data. Using this technique, the power spectrum of remitted light from the barrel region was found to peak within +/- 0.12 Hz of the inter-event interval frequency.

Algorithms↗
PubMed2004

Spatial frequency-dependent feedback of visual cortical area 21a modulating functional orientation column maps in areas 17 and 18 of the cat.

The feedback effect of activity of area 21a on orientation maps of areas 17 and 18 was investigated in cats using intrinsic signal optical imaging. A spatial frequency-dependent decrease in response amplitude of orientation maps to grating stimuli was observed in areas 17 and 18 when area 21a was inactivated by local injection of GABA, or by a lesion induced by liquid nitrogen freezing. The decrease in response amplitude of orientation maps of areas 17 and 18 after the area 21a inactivation paralleled the normal response without the inactivation. Application in area 21a of bicuculline, a GABAa receptor antagonist caused an increase in response amplitude of orientation maps of area 17. The results indicate a positive feedback from high-order visual cortical area 21a to lower-order areas underlying a spatial frequency-dependent mechanism.

Animals↗
PubMed2002

Information optimization in coupled audio-visual cortical maps.

Barn owls hunt in the dark by using cues from both sight and sound to locate their prey. This task is facilitated by topographic maps of the external space formed by neurons (e.g., in the optic tectum) that respond to visual or aural signals from a specific direction. Plasticity of these maps has been studied in owls forced to wear prismatic spectacles that shift their visual field. Adaptive behavior in young owls is accompanied by a compensating shift in the response of (mapped) neurons to auditory signals. We model the receptive fields of such neurons by linear filters that sample correlated audio-visual signals and search for filters that maximize the gathered information while subject to the costs of rewiring neurons. Assuming a higher fidelity of visual information, we find that the corresponding receptive fields are robust and unchanged by artificial shifts. The shape of the aural receptive field, however, is controlled by correlations between sight and sound. In response to prismatic glasses, the aural receptive fields shift in the compensating direction, although their shape is modified due to the costs of rewiring.

Acoustic Stimulation↗
PubMed1992

Optical imaging of epileptiform and functional activity in human cerebral cortex.

Optical imaging of animal somatosensory, olfactory and visual cortices has revealed maps of functional activity. In non-human primates, high-resolution maps of the visual cortex have been obtained using only an intrinsic reflection signal. Although the time course of the signal is slower than membrane potential changes, the maximum optical changes correspond to the maximal neuronal activity. The intrinsic optical signal may represent the flow of ionic currents, oxygen delivery, changes in blood volume, potassium accumulation or glial swelling. Here we use similar techniques to obtain maps from human cortex during stimulation-evoked epileptiform afterdischarges and cognitively evoked functional activity. Optical changes increased in magnitude as the intensity and duration of the afterdischarges increased. In areas surrounding the afterdischarge activity, optical changes were in the opposite direction and possibly represent an inhibitory surround. Large optical changes were found in the sensory cortex during tongue movement and in Broca's and Wernicke's language areas during naming exercises. The adaptation of high-resolution optical imaging for use on human cortex provides a new technique for investigation of the organization of the sensory and motor cortices, language, and other cognitive processes.

Brain Mapping↗
PubMed1993

Central retinal area is not the site where ganglion cells are generated first.

The development of retinal ganglion cells (RGC) was studied in the chick from stage 18 to adulthood. Our main objectives were to identify the retinal site where the first RGCs differentiate, to locate this site relative to the optically defined central retinal area, and to map the spatial arrangement of the RGC field at different stages in development. The eyes of the experimental animals were fixed and serially sectioned. The borders of RGC fields were determined from the presence of either ganglion cell perikarya or ganglion cell axons. In seven cases between stages 21 and 26, the borders of the RGC fields were confirmed electron microscopically. The serial sections together with the RGC fields were then reconstructed in three dimensions. The reconstructed retinae were projected onto a plane by using the radially equidistant polar azimuthal projection. First, RGCs appear dorsal to the apex of the optic fissure. Ganglion cell development then initially spreads out symmetrically with respect to the optic fissure. However, from stage 29 on, the nasal half of the retina expands much more than the temporal half. This asymmetrical growth entails that the optic fissure is eventually located in the temporal half of the retina in the mature animal. The RGC fields of the embryonic stages were superimposed on the retina of a visually active animal according to their real size and position. It turned out that the central retinal area was at least 2 mm away from the site where the first RGCs were generated. It is not before stage 28 that the prospective central retinal area is included into the expanding ganglion cell field. The fact that RGCs at the central retinal area are generated 2.5 days later than first RGCs near the apex of the optic fissure has important implications for the formation of the retinotectal projection.

Animals↗
PubMed2000

Temporal and topographical characterization of language cortices using intraoperative optical intrinsic signals.

We used intraoperative optical imaging of intrinsic signals (iOIS) and electrocortical stimulation mapping (ESM) to compare functionally active brain regions in 10 awake patients undergoing neurosurgical resection. Patients performed two to four tasks, including visual and auditory naming, word discrimination, and/or orofacial movements. All iOIS maps included areas identified by ESM mapping. However, iOIS also revealed topographical specificity dependent on language task. In Broca's area, naming paradigms activated both anterior and posterior inferior frontal gyrus (IFG), while the word discrimination paradigm activated only posterior IFG. In Wernicke's area, object naming produced activations localizing over the inferior and anterior/posterior regions, while the word discrimination task activated superior and anterior cortices. These results may suggest more posterior phonological activation and more anterior semantic activations in Broca's area, and more anterior/superior phonological activation and more posterior/inferior semantic activations in Wernicke's area. Although similar response onset was observed in Broca's and Wernicke's areas, temporal differences were revealed during block paradigm (20-s) activations. In Broca's area, block paradigms yielded a boxcar temporal activation profile (in all tasks) that resembled response profiles observed in motor cortex (with orofacial movements). In contrast, activations in Wernicke's area responded with a more dynamic profile (including early and late peaks) which varied with paradigm performance. Wernicke's area profiles were very similar to response profiles observed in sensory and visual cortex. The differing temporal patterns may therefore reflect unique processing performed by receptive (Wernicke's) and productive (Broca's) language centers. This study is consistent with task-specific semantic and phonologic regions within Broca's and Wernicke's areas and also is the first report of response profile differences dependent on cortical region and language task.

Brain↗