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Results for “Visual Pathways”

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At least 217 records · Page 12Linked to original sources
PubMed1994

The timing of processing along the visual pathway in the cat.

We obtained visual response latencies and response durations following visual stimulation of neurones recorded in the lateral geniculate nucleus (LGN), areas 17, 18, 19, the posteromedial lateral suprasylvian sulcus (PMLS), and area 7 of the cat. We found an increasing lengthening of the mean response latencies, consistent with the view of a progressive advance of processing from stage to stage. However, we also observed a substantial and increasing scatter in these latencies. Moreover, response durations vastly supersede this gradual increase in latencies. Taken together, these results suggest that most of the neurones within different stages of a hierarchically organized sensory pathway are simultaneously active when stimulated. Implications of a time-based processing scheme for models of information processing in highly interconnected, multi-layered systems are discussed.

Animals↗
PubMed1995

Distribution of calcium-binding proteins within the parallel visual pathways of a primate (Galago crassicaudatus).

Bush babies possess three distinct parallel pathways to striate cortex (V1 or area 17). The calcium-binding proteins parvalbumin (PV) and calbindin (CB) typically show complementary regional distributions in the brain, often associated with specific aspects of functionally related groups of cells. We asked whether PV+ and CB+ immunoreactivity differentiate central visual parallel pathways in this species. Results show that PV and CB cell and neuropil staining is strongly complementary in the lateral geniculate nucleus (LGN) and is associated with separate parallel pathways. CB+ immunoreactivity is dense, but cytochrome oxidase (CO) staining is light in the paired koniocellular layers. PV+ and CO+ immunoreactivity is most dense in the parvocellular and magnocellular layers. Combined analyses of cell size, retrograde labeling, and double labeling have confirmed that all PV+ and CB+ LGN cells are geniculocortical relay cells; none was found to be gamma-aminobutyric acid (GABA)ergic. In V1, dense PV+ neuropil closely matches the expression of CO in layer 4 and in the blobs of layer 3. CB+ staining is most dense in layers 2 and 3A and is not strongly expressed within the CO interblobs. Finally, PV and CB are not found in related parallel pathway components in the LGN and V1 (e.g., in V1, CO blobs exhibit dense PV+ neuropil, yet they are targets of the small K geniculocortical relay cells that are CB+ in the LGN). Our findings support the view that three functionally distinct visual pathways project to V1 from the LGN. However, the differences in the patterns of localization of PV and CB in the LGN and in V1 suggest that these proteins may be utilized in different ways in these two visual areas.

Animals↗
PubMed1993

Visual pathways supporting perception and action in the primate cerebral cortex.

Behavioral and electrophysiological evidence suggests a new interpretation of the division of labor between the ventral and dorsal streams of visual processing in primate cerebral cortex. It is suggested that the ventral stream mediates the perception of objects while the dorsal stream mediates the on-line control of skilled actions directed at those objects.

Animals↗
PubMed1996

Developmental tumour of the visual pathways. Report of an unusual case.

An unusual case of congenital hydrocephalus and visual loss due to developmental tumour of optic pathways is described. Diffuse, uniform and symmetrical replacement and enlargement of optic nerves, chiasma and optic tracts resulted in remarkable computerized tomographic (CT) scan images not yet described in the literature. Embryo-pathogenesis of this anatomical configuration of the neoplasm outlining the enlarged visual pathways in their entirety is discussed. The relevant literature is reviewed.

Blindness↗
PubMed1979

Visual pathways.

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Animals↗
PubMed1999

Infantile cerebral aneurysms with visual pathway compression.

Intracranial aneurysms are rare in infancy. The commonest presentation is intracranial hemorrhage, but signs of mass effect are more frequent than in adults. We report 2 infants with cerebral aneurysms, one presenting with macrocephaly and another with strabismus. Both had visual loss and optic disc pallor; MRI revealed a suprasellar mass and anterior visual pathway compression. In both cases, the preoperative diagnosis was craniopharyngioma. It is essential to recognize that, although exceedingly uncommon, cerebral aneurysms do occur in infants and have features that differ from those in adults.

Calcinosis↗
PubMed1997

The prevalence of strabismus in congenital nystagmus: the influence of anterior visual pathway disease.

PURPOSE: To determine the influence of underlying visual system disorders on the risk of developing strabismus in children with congenital nystagmus. METHODS: We retrospectively reviewed 82 cases of congenital nystagmus from a pediatric ophthalmology referral practice. RESULTS: Strabismus was found in 50% of children with congenital nystagmus. The prevalence of strabismus was 82% in children with bilateral optic nerve hypoplasia, 53% in patients with albinism, 36% in children with congenital retinal dystrophies, and 17% in children with idiopathic congenital nystagmus. CONCLUSION: The risk that a child with congenital nystagmus will have strabismus develop can be predicted from the nature of the underlying visual disorder.

Adolescent↗
PubMed1999

[Long-term outcome of gliomas of the visual pathway in type 1 neurofibromatosis].

BACKGROUND: Optic gliomas are frequently associated with neurofibromatosis type 1 (NF1) and belong to the diagnostic criteria of NF1. Different growth rates require differentiated strategies for screening and observation. PATIENTS AND METHODS: 29 patients (25 children < 11 years, 4 adults > 18 years) with visual pathway tumors and NF1 were examined neurologically, ophthalmogically, by means of MRI and VEP. Results were set into context with preceding investigations (mean follow up time 6.5 years). RESULTS: 11 children showed a stable condition, 14 an unfavorable process with substantial loss of vision. Children with an unfavorable process showed a lower age at diagnosis (3.2 versus 5.8 years; p < 0.05), more frequently strabism (11/14 versus 1/11; p < 0.05), optic atrophy (12/14 versus 1/11; p < 0.05), pathological VEP (9/9 versus 2/10; p = 0.001), visual field defects (9/9 versus 1/9) and involvement of the optic chiasm (11/14 versus 3/11; p < 0.05) than children with a stable condition. 3 of 4 adults had no visual symptoms despite involvement of the optic chiasm. CONCLUSIONS: The crucial prognostic factor is the patient's age at the time of diagnosis. Optic gliomas which become symptomatic in early childhood (< 6 years) grow rapidly and require frequent ophthalmologic investigations and MRI. Tumors diagnosed in late childhood (> 6 years) do not progress, allowing for gradual extension of intervals between ophthalmological investigations.

Adolescent↗
PubMed1997

On the structure and function of the tectofugal visual pathway in laterally eyed birds.

Of the two visual systems in vertebrates, the tectofugal pathway has often been attributed to stimulus localization, while the thalamofugal pathway was thought to be involved in stimulus identification. This review provides evidence that the tectofugal pathway serves both functions. It is speculated that the initial task of the tectum is to localize an object and to guide the fixation movement. The object in focus is then analysed by the higher stations of the tectofugal system. The result of the analysis is fed into the optic tectum and is used for decision about the treatment of the object.

Animals↗