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At least 343 records · Page 19Linked to original sources
PubMed1991

A new anatomical representation of the human visual pathways.

A three-dimensional, computer-aided reconstruction of the intracranial parts of the visual system, optic nerve, optic chiasm, optic tract, lateral geniculate body, optic radiation and striate area on the basis of anatomical serial cuts is presented in this paper. The computer-graphic representation simulates the illumination of a three-dimensional reconstruction. This study depicts for the first time a detailed anatomical reconstruction and illustrative representation of the striate area. An interactive investigation of the structure on the screen as well as a demonstration of the intracranial relationships between different neuroanatomical structures and comparisons with magnetic resonance, computed tomographic, and positron emission tomographic images is possible, providing that the neuroimaging uses the identical Cartesian coordinate system [22].

Aged↗
PubMed2004

Visual stimulation, 1H MR spectroscopy and fMRI of the human visual pathways.

The purpose was to assess changes in lactate content and other brain metabolites under visual stimulation in optical chiasm, optic radiations and occipital cortex using multiple voxel MR spectroscopy (MRS). 1H chemical shift imaging (CSI) examinations of transverse planes centered to include the above structures were performed in four subjects at an echo time of 135 ms. Functional MRI (fMRI) was used to confirm the presence of activity in the visual cortex during the visual stimulation. Spectral maps of optical chiasm were of poor quality due to field disturbances caused by nearby large blood vessels and/or eye movements. The optic radiations and the occipital lobe did not show any significant MR spectral change upon visual stimulation, i.e., the peak areas of inositol, choline, creatine, glutamate and N-acetylaspartate were not affected. Reproducible lactate signals were not observed. fMRI confirmed the presence of strong activations in stimulated visual cortex. Prolonged visual stimulation did not cause significant changes in MR spectra. Any signal observed near the 1.33 ppm resonance frequency of the lactate methyl-group was artifactual, originating from lipid signals from outside the volume of interest (VOI). Previous claims about changes in lactate levels in the visual cortex upon visual stimulation may have been based on such erroneous observations.

Adult↗
PubMed1996

Interaction of motion and color in the visual pathways.

In recent years the idea of parallel and independent processing streams for different visual attributes has become a guiding principle for linking the organization, architecture and function of the visual system. Findings concerning the segregation of motion and color information have been at the forefront of the evidence in favor of the parallel processing scheme. A number of studies have shown that motion perception is impaired for isoluminant stimuli, which are thought to isolate the color system. However, there are now many studies, the results of which are incompatible with the simple idea of segregated pathways. We propose two processing streams for motion that differ mostly in their temporal characteristics. Although neither of the two motion streams is color-blind, as was originally suggested, they differ radically in the way they process color information. The view that we propose provides a framework that reconciles a number of seemingly contradictory results. Evidence to support the new framework comes from psychophysical, physiological and lesion studies.

Color↗
PubMed2003

Age-related changes in the dynamics of human albino visual pathways.

A deficiency of melanin in the retinal pigment epithelium, which regulates the development of neural retina, leads to chiasmal misrouting such that the uncrossed pathway (to the ipsilateral hemisphere) is reduced relative to the crossed pathway (to the contralateral hemisphere). This study examines age-related changes in the flash and pattern appearance visual evoked potentials (VEP) of human albinos. Scalp recorded cortical VEPs to flash (FVEP) and pattern appearance stimulation were recorded in 58 albino (8 months to 60 years) and 34 normal subjects (4-55 years). VEPs were analysed by amplitude and latency. The contralateral hemisphere FVEP amplitude decreased with age in albino subjects, as in both hemispheres in normals. However, the ipsilateral hemisphere FVEP amplitude was significantly lower in young albino subjects, initially giving a marked interhemispheric asymmetry, but this normalized with age. Significant interhemispheric FVEP latency asymmetries were not observed. The contralateral pattern appearance VEP latency in albino subjects decreased with age, as in both hemispheres in normals; the ipsilateral latency increased significantly with age. Significant interhemispheric pattern appearance VEP amplitude asymmetries were not observed. These novel and unexpected observations indicate significant age-related changes in the retinocortical pathways of the human albino. These changes have implications for our understanding of development and plasticity of the central visual pathways.

Adolescent↗
PubMed2002

Electrophysiology of the postreceptoral visual pathway in mice.

Pattern VEPs have been recorded locally from the binocular portion of the primary visual cortex of wild type- and different transgenic mice by means of microelectrodes. Local pattern VEPs have been used on the one hand to obtain information on basic cortical layout (topography, laminar analysis) and ocularity (relative contribution of the contralateral and ipsilateral eye), and on the other hand to evaluate several aspects of visual physiology that have a counterpart in visual behavior (visual acuity, contrast sensitivity, motion sensitivity, response latency). As compared to visual behavior, pattern VEPs offer the advantage that several aspects of vision can be evaluated in the same animals, including those with poor behavior due to motor- or cognitive deficits, even during the postnatal development. Pattern VEPs provide a means for characterizing the visual phenotype of mutant mice and for the evaluation of the effects induced by experimental manipulation.

Animals↗
PubMed1991

Common projection areas of antennal and visual pathways in the honeybee brain, Apis mellifera.

The convergence of primary sensory neurons of the antennae, higher order visual interneurons, and antennal motoneurons was analysed with neuroanatomical techniques in the honeybee, Apis mellifera. The different modalities evoke specific antennal responses in this insect. Three different fluorescent dyes were applied successively in the same preparation in order to visualise the various fiber projections from the antennae and the lobula in the brain of the honeybee. Three neuropile areas where sensory fibers of the antennae overlap with visual projection neurons from the lobula were found. Within the posterior-median protocerebrum the antennal tract T6-1 comes in close vicinity to the lobula tract LoT-9 and to some other lobula fibers that cannot be assigned to a special tract. Antennal T6-3 fibers overlap with lobula LoT-7 neurons within the posterior protocerebrum more laterally. Antennal T5 fibers arborise in the dorsal lobe and show common projection sites with lobula LoT-3 neurons. The multimodal convergence in the three common neuropiles demonstrates that these areas are important centers for multimodal information processing between sensory, motor, and descending neurons in insects.

Animals↗
PubMed2003

[Tractography of the visual pathways: routine examination in magnetic resonance imaging].

Water diffusion analysis in magnetic resonance imaging (MRI) provides an elective visualization of fiber tract orientations in cerebral white matter, especially for optic tracts. We explored 25 patients from 18 to 45 years of age, with normal MRI in 20 subjects, and radiological anomalies in five. On a 1.5 Tesla MRI apparatus, diffusion tensor acquisitions were performed in 5 minutes 58 seconds with an EPI Single Shot sequence covering the entire brain. Image displacements were precluded by patient information and adequate fixation, then digitally corrected on workstations. Volume merging and fiber tract extraction were achieved using dedicated software (Volume-One and dTV). A directional depiction was obtained for all areas in the white matter, in particular for white matter junctions. Coming from the lateral geniculate body, the optic tracts were directed posteriorly toward the occipital cortex, with numerous connections to extrastriate associative areas, and through the corpus callosum and the fornix. Diffusion tractography requires optimization of volume displacements, before and secondary to MRI acquisitions. Our diffusion tensor acquisition, with image optimization in a short-duration sequence can be routinely applied to all patients, for a specific analysis of functional connections between cortical areas of cerebral white matter.

Adolescent↗
PubMed1989

Cavernous angiomas of the anterior visual pathways.

Three patients with cavernomas of the optic nerve, chiasm, or optic tract are presented. All suffered progressive visual loss due to local hemorrhage and the space-occupying effects of the vascular malformation. Computed tomography scans revealed small lesions with mild contrast enhancement in the suprasellar and parasellar cisterns, whereas angiography was unremarkable. Magnetic resonance imaging was helpful in our cases both for diagnosis and for planning surgical approach, showing typical signs of cavernomas as confirmed by subsequent surgery and histological examination. The clinical and intraoperative findings are presented.

Adolescent↗
PubMed1979

[Computerized tomography -- results in affections of the chiasm and visual pathway (author's transl)].

272 cases with visual field defects were examined by CT and analysed. 78 patients showed a chiasmatic lesion, 45 patients a lesion of the optic tract or the lateral geniculate body and 136 patients a lesion of the optic radiation or the occipital cortex. 96% of the CT pictures were topographically corresponding to the known optic field defect. In more then 75% of the operated patients the nature of the CT lesion was confirmed. 10 cases were negative in CT and 3 false positive. Because of the high rate of exact topographic diagnosis CT should be the initial investigation in visual field defects. But the nature of a lesion has to be diagnosed with caution, taking into account the entire clinical picture.

Adolescent↗