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At least 325 records · Page 18Linked to original sources
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↗
PubMed2003

Increasing depth of binocular rivalry suppression along two visual pathways.

Binocular rivalry refers to the alternating perception that occurs when the two eyes are presented with incompatible stimuli: one monocular image is seen exclusively for several seconds before disappearing as the other image comes into view. The unseen stimulus is physically present but is not perceived because the sensory signals it elicits are suppressed. The neural site of this binocular rivalry suppression is a source of continuing controversy. We psychophysically tested human subjects, using test probes designed to selectively activate the visual system at a variety of processing stages. The results, which apply to both form and motion judgements, show that the sensitivity loss during suppression increases as the subject's task becomes more sophisticated. We conclude that binocular rivalry suppression is present at a number of stages along two visual cortical pathways, and that suppression deepens as the visual signal progresses along these pathways.

Adult↗
PubMed1981

Confrontation visual field techniques in the detection of anterior visual pathway lesions.

The accuracy of a variety of finger and color confrontation tests in identifying chiasmal and optic nerve visual field defects was assessed in patients whose field defects had been established beforehand by a conventional achromatic kinetic technique on the Goldmann perimeter. Kinetic and static finger confrontation methods identified an average of 42% of the 28 chiasmal hemianopic defects. False negatives included eyes with hemianopias complete to the largest (V4e) Goldmann isopter. False positives (average, 15%) occurred in eyes containing nerve fiber bundle defects with borders that fell near the vertical fixational meridian. Kinetic and static color confrontation techniques were 78.6% sensitive to hemianopias. Accuracy did not differ significantly whether the red target was presented kinetically or statically against the tangent screen, projected on the Autoplot screen, or held in the examiner's hand without attention to background. False positives (average, 23%) were slightly greater than with finger confrontation methods and occurred not only in eyes with nerve fiber bundle defects but also in eyes with no defects in reference visual fields. Finger confrontation identified 11% or fewer of optic nerve field defects, while some color techniques detected as many as 31 1/3%. There were no false positives.

Hemianopsia↗
PubMed1994

Uhthoff's symptom in disorders of the anterior visual pathways.

To determine the frequency and clinical characteristics of Uhthoff's symptom, I studied 100 consecutive patients with pregeniculate visual loss of diverse etiology. Eighteen patients reported Uhthoff's symptom. Although there was a significant association of Uhthoff's symptom with multiple sclerosis (10 patients), other etiologies for this symptom included tumor (3 patients), optic neuropathy or papillitis (3 patients), aneurysm, and orbital pseudotumor (1 patient each). There was no link between the severity of visual loss, as measured by diminished acuity, field loss, or binocular involvement, and Uhthoff's symptom.

Adult↗
PubMed1999

A VEP investigation of parallel visual pathway development in primary school age children.

Different features of visual function mature along unique timescales through infancy and early childhood. It is not clear which functions continue to mature in school age children. Functions believed to be mediated by the Magnocellular (M) and Parvocellular (P) pathways were compared in five- (n=25), eight- (n=21) and eleven-year-old children (n=21) and young adult controls (n=20). Steady-state visual evoked potentials were recorded from occipital electrodes in response to very low spatial frequency gratings, at a series of contrasts (M), and to high contrast gratings at a series of spatial frequencies (P). No evidence was found to indicate M pathway development across these age groups. However, the youngest children demonstrated elevated VEP thresholds to the high contrast gratings compared with either the adults or eleven-year-olds. This difference in threshold implies an immaturity of the high contrast, high spatial frequency stream, i.e. the putative P pathway.

Adult↗