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At least 703 records · Page 39Linked to original sources
PubMed1988

Visual evoked potentials in tumors from orbita to occipital lobe in childhood.

68 infants and children with proven tumours along the visual pathway visually evoked potentials with pattern reversal and flash were investigated. Subdivided in 5 locational groups (orbital, optic nerve, chiasmatic, retrochiasmatic and occipital lobe) best results were obtained by stimulation with pattern reversal using variable checksizes (91.2%) versus 61.8% by using flash evoked responses. Furthermore, using patterned stimuli not only latency shifts are best detected but also hints for visual function correlating to visual acuity could be given also in nonverbal or disabled children. For long term follow-up studies in known space-occupying lesions along the visual pathway, the use of pattern VEP is extraordinary because of its high sensitivity and complete harmlessness. Pattern VEP are even more sensitive than visual acuity testing in cooperative patients. The close interdisciplinary follow-up controls in these children between pediatric neurophysiologists and neurosurgeons are, therefore, strongly recommended.

Adolescent↗
PubMed1995

Visual evoked potential abnormalities in jaundiced Gunn rats treated with sulfadimethoxine.

The manifestations of bilirubin encephalopathy include disturbances in the visual pathway (visual gaze paralysis and distorted visual perception). In the young jaundiced Gunn rat (jj) model of hyperbilirubinemia, significant differences in visual evoked potential (VEP) patterns have been recorded during development. In the present study, the effects of sulfadimethoxine (SDM) on VEP and electroretinogram (ERG) were examined in 3-wk-old jj rats. This drug displaces bilirubin from its albumin binding sites in the circulation, shifting it into tissues including the brain. Marked latency prolongations (11-20%) and reduced amplitudes (20-64%) were observed in the different wave components of the VEP. These changes were evident as early as 2 h after injection of the drug and persisted thereafter for another 4 h. On the other hand, ERG changes (significant prolongation of wave b) became apparent in these animals only 6 h after SDM injection. These results suggest that, although some changes in the retina may occur after a massive entry of bilirubin into the nervous system, the primary damage in the visual pathway after bilirubin exposure is probably beyond the retina.

Animals↗
PubMed1997

Neuroradiological assessment of visuoperceptual disturbance in children with spina bifida and hydrocephalus.

The intellectual status of twelve children with spina bifida and hydrocephalus was evaluated. Seven children were considered to have verbal and non-verbal skill discrepancies. It was considered that the Verbal IQ-Performance IQ score by WISC-R could be used as an index of their visuoperceptual disturbance. The disturbance was closely related to the morphological characteristics of the lateral ventricles on cerebral MRI. The ratio of the areas of the posterior horns to the anterior horns (P:A) showed a negative correlation with visuoperceptual ability. The visual pathway, visual cortex, and the ventral system were thus considered to be the sites of the affected lesions. From P:A changes with time, it was evident that adequate shunting would prevent the perceptual disturbance.

Adolescent↗
PubMed1994

Separate neural pathways for the visual analysis of object shape in perception and prehension.

BACKGROUND: Earlier work with neurological patients has shown that the visual perception of object size and orientation depends on visual pathways in the cerebral cortex that are separate from those mediating the use of these same object properties in the control of goal-directed grasping. We present evidence suggesting that the same dissociation between perception and action is evident in the visual processing of object shape. In other words, discrimination between objects on the basis of their shape appears to be mediated by visual mechanisms that are functionally and neurally distinct from those controlling the pre-shaping of the hand during grasping movements directed at those same objects. RESULTS: We studied two patients with lesions in different parts of the cerebral visual pathways. One patient (RV), who had sustained bilateral lesions of the occipitoparietal cortex, was unable to use visual information to place her fingers correctly on the circumference of irregularly shaped objects when asked to pick them up, even though she had no difficulty in visually discriminating one such object from another. Conversely, a second patient (DF), who had bilateral damage in the ventrolateral occipital region, had no difficulty in placing her fingers on appropriate opposition points during grasping, even though she was unable to discriminate visually amongst such objects. CONCLUSIONS: This double dissociation lends strong support to the idea that the visual mechanisms mediating the perception of objects are functionally and neurally distinct from those mediating the control of skilled actions directed at those objects. It also supports the recent proposal of Goodale and Milner that visual perception depends on a ventral stream of projections from the primary visual cortex to the inferotemporal cortex, whereas the visual control of skilled actions depends on a dorsal stream from the primary visual cortex to the posterior parietal cortex.

Adult↗
PubMed1997

Cerebral visual impairment in preterm infants with periventricular leukomalacia.

Neonatal brain lesions are the main cause of cerebral visual impairment in infancy, i.e., of a visual deficit caused by damage to posterior visual pathways. Visual outcome of preterm infants with periventricular leukomalacia (PVL) was investigated in 14 subjects affected by severe cystic PVL, another 34 with moderate PVL (prolonged periventricular echodensities), and 18 control preterm infants. All cases with significant ocular abnormalities (such as retinopathy of prematurity state III or upwards, optic nerve atrophy, or major refraction problems) were excluded. Visual acuity, visual field, eye alignment, fixation and following, optokinetic nystagmus, and visual threat were tested at 1 year of corrected age. A high incidence of cerebral visual impairment, consisting mainly of low visual acuity, severe oculomotor disorders, and reduced visual field, was found in infants with severe PVL. Visual defects were less frequent and less severe in the moderate PVL group, and very rare in the control group. The results of neuroimaging, and especially of magnetic resonance imaging, correlated with the visual outcome and indicate lesions at the level of optic radiations as the main anatomic substrate of the visual impairment. All infants with PVL need a visual follow-up, from the first months of life, the results of which are important both for visual and motor rehabilitation of these cases and for their daily care.

Female↗
PubMed2004

How parallel is visual processing in the ventral pathway?

Visual object perception is usually studied by presenting one object at a time at the fovea. However, the world around us is composed of multiple objects. The way our visual system deals with this complexity has remained controversial in the literature. Some models claim that the ventral pathway, a set of visual cortical areas responsible for object recognition, can process only one or very few objects at a time without ambiguity. Other models argue in favor of a massively parallel processing of objects in a scene. Recent experiments in monkeys have provided important data about this issue. The ventral pathway seems to be able to perform complex analyses on several objects simultaneously, but only during a short time period. Subsequently only one or very few objects are explicitly selected and consciously perceived. Here, we survey the implications of these new findings for our understanding of object processing.

Consciousness↗
PubMedDate not supplied

Differing non-additive alterations in different parts of the nervous system of the rat.

Synergistic loss of auditory sensitivity has been observed after combined exposure to xylene and n-hexane, and to toluene and n-hexane. After these combined exposures, antagonisms were seen in the auditory pathway, visual pathway, peripheral nerve and testes. synergistic interaction in one part of the nervous system and antagonistic interaction in another part has also been seen after combined exposure to toluene and dichloromethane. Two conclusions can be drawn from these observations: (1) an antagonism seen in one part of the nervous system after exposure to a specific combination of chemicals does not exclude the possibility of a synergism in other parts; and (2) both synergism and antagonism can occur within the same neurosensory organ after identical combined exposure. The observed, presumably cochlear, loss of auditory sensitivity after exposure to xylene and n-hexane was synergistic, while antagonism was found in the auditory pathway. These observations suggest that extrapolation of the combined effect in one part of the nervous system to another part, even within the same organ system, can be unreliable.

Animals↗
PubMed1985

Permanent cortical visual impairment in children.

Fifty patients with permanent cortical visual impairment were evaluated. They had a characteristic behaviour profile, usually with residual sight but poor visual attention. 30 of the 50 also had damage to the anterior visual pathway. Visual evoked potential mapping was shown to have a clear advantage over visual evoked responses, and using that in conjunction with CT and clinical data enabled several subgroups of cortical visual impairment to be identified. The diagnosis probably is more common than previously recognised, and should be suspected when there is greater delay in visual development in other areas and the degree of visual loss is unexplained by ocular findings. Using traditional criteria for cortical blindness may mean that many children are not diagnosed, which has serious implications for their rehabilitation.

Adolescent↗