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At least 199 records · Page 11Linked to original sources
PubMed1993

Unilateral atrophy of the optic nerve associated with retrograde and anterograde degenerations in the visual pathways in Slc: Wistar rats.

Unilateral degenerative atrophy of the optic nerve (ON) occurred in 6 of 80 male and 4 of 80 female Slc: Wistar rats. Two of these cases completely lost the intracranial portion of the unilateral ON and the remainder had the small ON. The optic disc and ON were located histologically in the posterior pole of the eyeball of 2 rats with no intracranial ON. ON lesions in all cases were characterized by a reduced number of axons with a small number of myelinated axons and marked astrogliosis. There were also swelling, fragmentation and spheroid formation of axons, as well as thickening of the connective tissue sheaths and vessel walls in the ON. One side of the optic chiasma and optic tract contralateral to the affected ON reduced in volume, became degenerated and were accompanied by gliosis. Focal or diffuse degeneration of the retina was observed in the eyeballs with affected ON. Retinal ganglion cells decreased in the number showing chromatolysis. These retinae became thin and developed degeneration of both inner and outer portions with sclerotic changes in the retinal vessels. The ophthalmic and ciliary arteries in the eyeballs with affected ON often developed proliferative or occlusive endoarteritis, suggesting that retinal lesions may have resulted not only from axonal degeneration in the ON but also from ischemia. Histologic lesions suggestive of transneuronal degeneration were found in the contralateral lateral geniculate body and rostral colliculus. Based on the data presented, it was presumed that a primary lesion may have been induced in the ON by a circulatory disturbance and followed by retrograde and anterograde degenerations in the visual pathways.

Animals↗
PubMedDate not supplied

Retinotopic order appears before ocular separation in developing visual pathways.

In mammals, the major subcortical visual structures receive projections from both eyes, with the uncrossed projection being smaller than the crossed. Each projection is arranged as a separate orderly map of one hemiretina. Although these hemiretinal maps are separate in the nuclei, they are aligned so that the representations of points in the visual field are in register, thus there is a continuity of visual field representation between them. During the early development of the binocular pathways, terminals from the two eyes overlap almost entirely. As development proceeds, terminals arising from each eye segregate to form the adult pattern. In the present study, local retinal lesions were made in ferrets at various stages in development before the separation of the projections from the two eyes. A neuronal tracer was then injected into the damaged eye, defining the pattern of projection from that eye. As reported here, the lesion resulted in a limited interruption in the pattern of terminal label on both sides of the brain, demonstrating that terminals from each eye are arranged in an orderly retinotopic manner at this stage. hence, during later development, as one projection is reduced relative to the other, the two maps must slide in relation to each other.

Albinism↗
PubMed1998

Protection of visual pathway in gamma knife radiosurgery for craniopharyngiomas.

Craniopharyngiomas present a major challenge to Gamma Knife radiosurgery (GKRS) due to their proximity to the optic apparatus. Based on observations of the evolving tumoral change on MRI and clinical results, an optimization of the treatment strategy and dose selection is possible. From March 1993 to September 1996, 21 patients with craniopharyngiomas were treated by GKRS. Every patient received stereotactic MRI exclusively for targeting and dose planning. The tumor and adjacent structures, including optic nerves, chiasm, and tracts were carefully identified and delineated on sagittal, coronal and axial films. The tumor volume ranged from 0.3 to 28 ml (average 9 ml). We purposefully apply multiple isocenters (average 9.1 shots) to create an isodose curve that covered the tumor optimally while sparing the optic pathway. The marginal dose prescribed was 9.5 to 16 Gy (50%). The maximal dose was 19 to 32 Gy. The maximal dose to the optic apparatus was 3.2 to 12.5 Gy. After GKRS, all patients were followed up clinically every month. MR studies were conducted every six months with the same techniques on the same scanner to investigate evolution of tumor volume and any adverse radiation effect. The follow-up period ranged from 6 to 40 months (mean: 18.4, median: 19). All patients were followed more than 6 months. Nineteen out of 21 cases (90.5%) achieved tumor control; that is, 18 tumor shrinkage (volume reduction: 15-95%) and 1 stabilized tumor growth. Among these 21 patients, 7 had improved visual acuity or visual field after GKRS, and the rest remained stable. Two patients developed mild T2 change on MRI without any endocrinological disturbance or visual impairment. Protection of the visual pathway can be secured by a sophisticated delineation on 3-dimensional stereotactic images with multiple-shot dose planning. Craniopharyngiomas with tumor volume up to 25 ml were treated safely and effectively, because the dose to the optic apparatus was kept as low as possiby this strategy. Further follow-up is needed to determine the highest tolerable dose to surrounding critical structures and the long-term outcome of tumor control.

Adolescent↗
PubMed1999

Spatial characteristics of the second-order visual pathway revealed by positional adaptation.

The visual system is thought to process luminance (first-order) and contrast (second-order) information by dedicated cortical streams. To explore the spatial characteristics of the second-order pathway, we examined the effect of adaptation on spatial localization in human subjects. We show that, unlike first-order adaptation, second-order positional adaptation via cortical mechanisms transfers across orientations but not across spatial frequencies. These results support physiological evidence that these two processing streams are distinct and suggest that the cortical mechanism mediating second-order positional adaptation maintains spatial frequency information but sums signals across orientations.

Adaptation, Ocular↗
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↗