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PubMed2005

Differential aging of chromatic and achromatic visual pathways: behavior and electrophysiology.

Aging of visual pathways was measured psychophysically and physiologically in subjects aged 20-89 years. Contrast thresholds for the chromatic pathways increased with age, but there were no significant changes for thresholds of the achromatic pathway at low spatial frequencies. For visual evoked potential (VEP) responses, again only the chromatic pathways were significantly affected by age. Age-related changes in chromatic responses were not apparent when stimuli were adjusted by age-related contrast thresholds. This suggests that the chromatic and achromatic visual pathways age differently and that the VEP accurately and objectively reflects behavioral changes with age.

Adult↗

PubMed2006

Investigation of Lewy pathology in the visual pathway of brains of dementia with Lewy bodies.

We examined 19 autopsied cases of dementia with Lewy bodies (DLB) using pathological and alpha-synuclein-immunohistochemical methods, and investigated Lewy pathology in the primary visual pathway (lateral geniculate body and Brodmann's area 17), secondary visual pathway (pulvinar, Brodmann's areas 18 and 19, and inferior temporal cortex), amygdala and substantia nigra, to clarify the relationship between visual misidentification and Lewy pathology in the visual pathway. Consequently, the secondary visual pathway revealed significantly severer Lewy pathology than the primary visual pathway, suggesting that the degeneration of the secondary visual pathway induces dysfunction in the recognition of objects shape and color. In addition, the amygdala revealed significantly severer Lewy pathology and neuronal loss than the primary and secondary visual pathways, suggesting that the degeneration of the amygdala, which receives the afferent connections from the substantia nigra, fails to modulate the visual processing according to cognition and emotion. These findings suggest that Lewy pathologies in the secondary visual pathway and amygdala may cause the dysfunction of the visuo-amygdaloid pathway and participate in visual misidentification in DLB patients. In addition, we compared Lewy pathology between cases with and without visual hallucinations, and showed no significant differences between the two groups.

Aged↗

PubMed1991

Efficacy and complications of radiotherapy of anterior visual pathway tumors.

A progressive disturbance in visual acuity or visual field, along with an unexplained optic nerve atrophy, suggests the possibility of a tumor. Tumors that frequently affect the anterior visual pathway include primary optic nerve sheath meningiomas, intracranial meningiomas, optic gliomas, pituitary tumors, and craniopharyngiomas. The location of these tumors sometimes prohibits a complete surgical excision that might jeopardize the visual system. Radiation therapy, however, can be beneficial in these cases. This article reviews the indications for radiotherapy of tumors that involve the anterior visual pathway, along with the possible complications. Cases that present the effect of radiation therapy and radiation damage are presented.

Adenoma↗

PubMed2004

Preventing recurrent opacification of the visual pathway after pediatric cataract surgery.

PURPOSE: To determine the rate of secondary opacification of the visual pathway following pediatric cataract surgery in children between the ages of 10 months and 7 years. METHODS: The medical records of children less than 7 years old who underwent lens aspiration, posterior chamber intraocular lens (IOL) implantation, primary pars plana posterior capsulectomy, and anterior vitrectomy were reviewed retrospectively. Twenty-six eyes in 19 children were included in the study. All procedures were performed by an anterior segment surgeon and a vitreoretinal surgeon. Main outcome measures were the prevalence of re-opacification of the visual pathway and of early postoperative complications. RESULTS: The visual pathway remained clear in 25 of 26 eyes (96%) after pediatric cataract surgery combined with primary pars plana posterior capsulectomy and anterior vitrectomy. The mean age at surgery was 46 +/- 23 months (+/-SD). Secondary opacification of the visual pathway occurred in one eye (4%), requiring another surgical procedure. At last follow-up (mean, 26 months; range, 6 to 79 months), the visual pathway was clear in all 26 eyes (100%). No cases of clinically significant IOL displacement or of retinal detachment were noted. CONCLUSIONS: For children undergoing pediatric cataract surgery between the ages of 10 months and 7 years, IOL implantation combined with primary pars plana posterior capsulectomy and anterior vitrectomy is effective in preventing re-opacification of the visual pathway.

Cataract↗

PubMed2002

Adaptive spatiotemporal receptive field estimation in the visual pathway.

The encoding properties of the visual pathway are under constant control from mechanisms of adaptation and systems-level plasticity. In all but the most artificial experimental conditions, these mechanisms serve to continuously modulate the spatial and temporal receptive field (RF) dynamics. Conventional reverse-correlation techniques designed to capture spatiotemporal RF properties assume invariant stimulus-response relationships over experimental trials and are thus limited in their applicability to more natural experimental conditions. Presented here is an approach to tracking time-varying encoding dynamics in the early visual pathway based on adaptive estimation of the spatiotemporal RF in the time domain. Simulations and experimental data from the lateral geniculate nucleus reveal that subtle features of encoding properties can be captured by the adaptive approach that would otherwise be undetected. Capturing the role of dynamically varying encoding mechanisms is vital to our understanding of vision on the natural setting, where there is absence of a true steady state.

Adaptation, Physiological↗

PubMed1998

Neural conduction in visual pathways in newly-diagnosed IDDM patients.

OBJECTIVES: Visual evoked potentials (VEPs) show abnormal responses in newly-diagnosed insulin-dependent diabetic (IDDM) patients. Electrophysiological methods allow one to dissect and explore different structures contributing to neural conduction in the visual pathways. The aim of our work was to assess whether the VEP abnormalities are due to impaired function of the retinal layers and/or a delayed conduction in the postretinal visual pathways. METHODS: Simultaneous recordings of VEP and pattern-electroretinogram (PERG) were performed at two intervals (at entry of the study and after 3 months) in 14 newly-diagnosed IDDM patients (age: 24.8+/-6.8 years; duration of disease: 3+/-1.5 months), and in 14 age-matched control subjects. RESULTS: In comparison with control subjects, IDDM patients showed: VEP P100 latencies significantly delayed (P < 0.01), a significant impairment of all PERG parameters (P < 0.01) and retinocortical time (RCT, difference between VEP P100 and PERG P50 latencies) and latency window (LW, difference between VEP N75 and PERG P50 latencies) also significantly increased (P < 0.01). All electrophysiological parameters were not significantly changed when retested after 3 months. No correlations were found between VEP P100 latency, RCT, LW and PERG parameters. CONCLUSIONS: Impaired PERG indicates an involvement of the innermost retinal layers; increased values of RCT and LW represent an index of delayed neural conduction in the postretinal visual pathways. Therefore two sources, one retinal (impaired PERG) and one postretinal (delayed RCT and LW), may independently contribute in to the abnormal responses of VEP observed in newly-diagnosed IDDM patients. Three months of relatively-stable metabolic control have not normalized the VEP and PERG impairment.

Adolescent↗

PubMed1999

Direct synaptic connections of axons from superior colliculus with identified thalamo-amygdaloid projection neurons in the rat: possible substrates of a subcortical visual pathway to the amygdala.

The aim of the present study was to identify synaptic contacts from axons originating in the superior colliculus with thalamic neurons projecting to the lateral nucleus of the amygdala. Axons from the superior colliculus were traced with the anterograde tracers Phaseolus vulgaris leucoagglutinin or the biotinylated and fluorescent dextran amine "Miniruby." Thalamo-amygdaloid projection neurons were identified with the retrograde tracer Fluoro-Gold. Injections of Fluoro-Gold into the lateral nucleus of the amygdala labeled neurons in nuclei of the posterior thalamus which surround the medial geniculate body, viz. the suprageniculate nucleus, the medial division of the medial geniculate body, the posterior intralaminar nucleus, and the peripeduncular nucleus. Anterogradely labeled axons from the superior colliculus terminated in the same regions of the thalamus. Tecto-thalamic axons originating from superficial collicular layers were found predominantly in the suprageniculate nucleus, whereas axons from deep collicular layers were detected in equal density in all thalamic nuclei surrounding the medial geniculate body. Double-labeling experiments revealed an overlap of projection areas in the above-mentioned thalamic nuclei. Electron microscopy of areas of overlap confirmed synaptic contacts of anterogradely labeled presynaptic profiles originating in the superficial layers of the superior colliculus with retrogradely labeled postsynaptic profiles of thalamo-amygdaloid projection neurons. These connections may represent a subcortical pathway for visual information transfer to the amygdala.

Amygdala↗

PubMed1989

A type II keratin is expressed in glial cells of the goldfish visual pathway.

The predominant intermediate filament proteins of the goldfish visual pathway consist of neuronal and non-neuronal isoelectric variants (58 kd). We have isolated a cDNA clone for the glial intermediate filament protein (ON3) from an optic nerve expression library. The predicted amino acid sequence of this clone reveals that it codes for a type II keratin representing the goldfish equivalent of mammalian keratin K8. K8 has been shown to be associated with embryogenesis and development. Unlike the mammalian visual system, the goldfish visual pathway displays a remarkable capacity for functional regeneration. The expression of K8, a protein not usually expressed in glial cells but shown to be associated with development, in the goldfish optic nerve may be involved with the processes of growth and regeneration in the goldfish visual pathway.

Amino Acid Sequence↗

PubMed1993

Pattern of organization of primary visual pathways in the European lizard Podarcis sicula Rafinesque.

Central visual pathways are similarly organized in all vertebrates, although differences are also evident in the distribution of retinofugal axons in mammals, birds and reptiles. We traced the retinofugal projections in the European lizard Podarcis sicula Rafinesque and compared our observations with previous findings in other reptilian species, as well as in mammals and in birds, in order to contribute to the understanding of similarities and differences in the pattern of organization of visual pathways in these vertebrate classes. Either HRP or 3H-proline injections were placed into one eye. No differences in staining pattern were observed between HRP and 3H-proline experiments. Prominent retinofugal projections were observed to the thalamic nuclei nucleus dorsolateralis, nucleus geniculatus lateralis dorsalis, nucleus geniculatus lateralis ventralis and nucleus geniculatus lateralis ventralis, pars ventralis. In the hypothalamus the suprachiasmatic nucleus, and in the pretectum nuclei geniculatus pretectalis, lentiformis mesencephali and posterodorsalis contained detectable amounts of labeled terminals. Retinal fibers were distributed to layers 14 and 12 of the optic tectum and terminated in layers 13, 11, and 8. Labeled fibers were also present in the basal optic tract, and terminals were located in the nucleus of the basal optic tract. Ipsilateral retinofugal fibers were detected in the optic tract, and terminals were observed in the same thalamic and pretectal nuclei which receive crossed projections. No terminals in the ipsilateral tectal layers could be demonstrated. Compared to the crossed projection, the ipsilateral retinofugal contingent was very small. These results confirm and extend data from previous studies in reptiles and are consistent with the distribution of retinofugal fibers found in other vertebrates. The presence of ipsilateral retinofugal projections represents a common feature of the organization of visual pathways in reptiles, although its importance for binocular interactions remains to be elucidated.

Animals↗

PubMed2004

PaVESy: Pathway Visualization and Editing System.

UNLABELLED: A data managing system for editing and visualization of biological pathways is presented. The main component of PaVESy (Pathway Visualization and Editing System) is a relational SQL database system. The database design allows storage of biological objects, such as metabolites, proteins, genes and respective relations, which are required to assemble metabolic and regulatory biological interactions. The database model accommodates highly flexible annotation of biological objects by user-defined attributes. In addition, specific roles of objects are derived from these attributes in the context of user-defined interactions, e.g. in the course of pathway generation or during editing of the database content. Furthermore, the user may organize and arrange the database content within a folder structure and is free to group and annotate database objects of interest within customizable subsets. Thus, we allow an individualized view on the database content and facilitate user customization. A JAVA-based class library was developed, which serves as the database programming interface to PaVESy. This API provides classes, which implement the concepts of object persistence in SQL databases, such as entries, interactions, annotations, folders and subsets. We created editing and visualization tools for navigation in and visualization of the database content. User approved pathway assemblies are stored and may be retrieved for continued modification, annotation and export. Data export is interfaced with a range of network visualization programs, such as Pajek or other software allowing import of SBML or GML data format. AVAILABILITY: http://pavsey.mpimp-golm.mpg.de

Database Management Systems↗

PubMed1988

Management of pregeniculate anterior visual pathway gliomas.

Gliomas of the pregeniculate anterior visual pathways comprise about 5% of all intracranial tumors that occur in the first decade of life. Gliomas are the most common primary optic nerve tumor. Diagnosing a glioma of the anterior visual pathways is much easier since the advent of computerized tomography (CT) and magnetic resonance imaging (MRI); the continuing problem is appropriate management. Improved guidelines for management are suggested based on a review of the literature and the authors' experience. These guidelines include both the need to characterize accurately the location of the tumor and its clinical and radiologic progression, and the imperative to employ active intervention only when there is a specific therapeutic goal that can be used for measuring the success of the treatment.

Child↗

PubMed1987

Irradiation of meningiomas of the intracranial anterior visual pathway.

Twenty patients with progressive visual loss caused by intracranial meningiomas involving the anterior visual pathway were treated with irradiation alone (n = 4) or with irradiation combined with tumor excision (n = 16). Improvement in visual performance occurred in 13 patients; 2 patients experienced temporary improvement; and 5 others maintained stable visual function for up to 9.5 years (mean follow-up, 4.0 years). Radiotherapy seemed to have no effect in 2 patients. One patient experienced temporary improvement, but eventually died from spread of tumor. Only one definite complication of radiotherapy occurred and was related to excessive radiation dose (greater than 7,000 cGy). Irradiation in the range of 5,000 to 5,500 cGy was effective either alone or in combination with surgical excision. Serial assessment of visual acuity and fields allowed us to demonstrate and quantify improvement in our patients following radiotherapy; in contrast, follow-up computed tomographic studies rarely demonstrated reduced tumor size.

Combined Modality Therapy↗

PubMed2006

Dynamic spatial processing originates in early visual pathways.

A variety of studies in the visual system demonstrate that coarse spatial features are processed before those of fine detail. This aspect of visual processing is assumed to originate in striate cortex, where single cells exhibit a refinement of spatial frequency tuning over the duration of their response. However, in early visual pathways, well known temporal differences are present between center and surround components of receptive fields. Specifically, response latency of the receptive field center is relatively shorter than that of the surround. This spatiotemporal inseparability could provide the basis of coarse-to-fine dynamics in early and subsequent visual areas. We have investigated this possibility with three separate approaches. First, we predict spatial-frequency tuning dynamics from the spatiotemporal receptive fields of 118 cells in the lateral geniculate nucleus (LGN). Second, we compare these linear predictions to measurements of tuning dynamics obtained with a subspace reverse correlation technique. We find that tuning evolves dramatically in thalamic cells, and that tuning changes are generally consistent with the temporal differences between spatiotemporal receptive field components. Third, we use a model to examine how different sources of dynamic input from early visual pathways can affect tuning in cortical cells. We identify two mechanisms capable of producing substantial dynamics at the cortical level: (1) the center-surround delay in individual LGN neurons, and (2) convergent input from multiple cells with different receptive field sizes and response latencies. Overall, our simulations suggest that coarse-to-fine tuning in the visual cortex can be generated completely by a feedforward process.

Action Potentials↗

PubMed2006

Peculiar and typical oligodendrocytes are involved in an uneven myelination pattern during the ontogeny of the lizard visual pathway.

We studied the myelination of the visual pathway during the ontogeny of the lizard Gallotia galloti using immunohistochemical methods to stain the myelin basic protein (MBP) and proteolipid protein (PLP/DM20), and electron microscopy. The staining pattern for the PLP/DM20 and MBP overlapped during the lizard ontogeny and was first observed at E39 in cell bodies and fibers located in the temporal optic nerve, optic chiasm, middle optic tract, and in the stratum album centrale of the optic tectum (OT). The expression of these proteins extended to the nerve fiber layer (NFL) of the temporal retina and to the outer strata of the OT at E40. From hatching onwards, the labeling became stronger and extended to the entire visual pathway. Our ultrastructural data in postnatal and adult animals revealed the presence of both myelinated and unmyelinated retinal ganglion cell axons in all visual areas, with a tendency for the larger axons to show the thicker myelin sheaths. Moreover, two kinds of oligodendrocytes were described: peculiar oligodendrocytes displaying loose myelin sheaths were only observed in the NFL, whereas typical medium electron-dense oligodendrocytes displaying compact myelin sheaths were observed in the rest of the visual areas. The weakest expression of the PLP/DM20 in the NFL of the retina appears to be linked to the loose appearance of its myelin sheaths. We conclude that typical and peculiar oligodendrocytes are involved in an uneven myelination process, which follows a temporo-nasal and rostro-caudal gradient in the retina and ON, and a ventro-dorsal gradient in the OT.

Age Factors↗

PubMedDate not supplied

[Visual pathways: a set of time-saving strategies].

INTRODUCTION: The visual pathways in our brain perform a practically impossible task: they are able to identify objects in tenths of a second in spite of having to process millions of data items. Studies being conducted in basic Neuroscience are beginning to discover the tricks that make this process possible. METHOD: These studies are based on two main pillars. First, we have an increasingly more detailed knowledge of the anatomy of the visual pathway. Second, the analyses of the receptive fields of the visual cells are becoming more and more sophisticated (each cell in the visual pathway responds to specific stimuli located within a tiny area of the space we call receptive field). Recent studies, including those conducted in my own laboratory, are beginning to reveal the pathways that give rise to different types of receptive fields and their possible function. CONCLUSION: The study of the different types of receptive fields provides us with important lessons about how images are processed. This paper offers a brief review of the current concepts that attempt to explain why such a complex task as sight gives the impression of being so simple.

Humans↗

PubMed2002

Visual pathway glioma in children treated with chemotherapy.

Visual pathway gliomas occur predominantly in young children. Chemotherapy has been increasingly used as a first-line treatment because of the complications caused by radiotherapy and surgery. Nine children between 6 months and 9 years (median age of 4.8 years) were treated with vincristine and carboplatin according to the SIOP (Société Internationale d'Oncologie Pédiatrique) low-grade glioma 1996 protocol. Five patients had evidence of neurofibromatosis type 1. Magnetic resonance imaging (MRI) and ophthalmological assessment were performed during and after treatment. There was a positive response in all children (100%). Three patients developed progressive disease between 8 and 12 months after ceasing treatment. One of them, being only 2.5 years old, was again treated by chemotherapy with partial response on MRI. Patients with neurofibromatosis type 1 never developed progressive disease. Our data suggest that chemotherapy is an effective treatment option in young children with visual pathway gliomas. MRI is an important means of monitoring the tumour response provided that a rigid imaging protocol is used to detect the early tumoral changes.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1999

Gliomas of the anterior visual pathways.

Gliomas of the anterior visual pathways include the more commonly encountered benign tumors of children and the rare and highly aggressive malignant tumors of adults. Diagnostic biopsy is not required in most cases of childhood gliomas, especially those unassociated with visual loss or other neurologic symptoms, because the clinical and neuroimaging features are often sufficiently characteristic. Because of the infiltrative nature of these tumors, the neurosurgeon has little to offer symptomatic patients beyond debulking large exophytic masses and shunting if hydrocephalus is present.

Adult↗

PubMedDate not supplied

Gliomas of the anterior visual pathway.

Gliomas of the anterior visual pathway are rare orbital lesions accounting for 65% of all intrinsic optic nerve tumors. These lesions occur principally among children in the first decade of life. They appear to be true neoplasms that characteristically show early growth, followed by stability in many patients. Visual prognosis is fair, and the outlook for life depends upon tumor location. When initially confined to the optic nerve alone, overall mortality is about 5%. Once the hypothalamus is involved, mortality rises sharply to over 50%. With involvement of the chiasm or hypothalamus, no form of therapy significantly alters the final outcome. Because of their indolent course, gliomas may be followed conservatively when confined to the optic nerve. In these cases, surgery is indicated only when blindness and pain or severe proptosis intervene. However, all such patients should be followed radiologically for evidence of posterior extension. When the chiasm is threatened, surgical excision via a craniotomy approach is warranted to prevent subsequent hypothalamic or third ventricle involvement. Malignant optic glioma is a distinct disease primarily affecting middle-aged adults. The chiasm is always involved, and although one eye may be spared initially, rapid progression to bilateral blindness is usual. The disease is uniformly fatal.

Adult↗