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PubMed2004

The mapping of the visual field onto the dorso-lateral tectum of the pigeon (Columba livia) and its relations with retinal specializations.

Most of the physiological studies of the pigeon retino-tectal visual pathway have investigated the accessible tectum, a small dorso-lateral tectal section that can be easily accessed by a simple craniotomy. However, at present we lack a detailed study of the topographical arrangement between the visual field, the retina and the accessible tectum. In particular, it is not known which section of the visual field is mapped onto the accessible tectum, and which of the specialized retinal areas mediates this projection. Here we determined, using local field potential (LFP) recordings and reverse retinoscopy, the shape, size and position in the visual space of the portion of the visual field mapped onto the accessible tectum (called here the accessible visual field, or AVF). Using this data and the mapping of Nalbach et al. [Vis. Res. 30 (4) (1990) 529], the retinal area corresponding to the AVF was determined. Such retinal area was also directly delimited by means of retrograde transport of DiI. The results indicate that the AVF is a triangular perifoveal zone encompassing only 15% of total visual field. The retinal region corresponding to the AVF has the shape of an elongated triangle that runs parallel to the visual equator and contains the fovea, the tip of the pecten, a perifoveal region of the yellow field and a small crescent of the red field. In agreement with this anatomical heterogeneity, visual evoked potentials measured in different parts of the accessible tectum present steep variations in shape and size. These results are helpful to better design and interpret anatomical and physiological experiments involving the pigeon's visual system.

Animals↗
PubMed2000

Glaucoma in primates: cytochrome oxidase reactivity in parvo- and magnocellular pathways.

PURPOSE: To evaluate the differential effects of ganglion cell depletion from experimental glaucoma on the relative metabolic activities of neurons in the parvo (P)- and magno (M)-cellular visual pathways of the macaque visual system. METHODS: Monocular experimental glaucoma was induced in monkeys (Macaca mulatta and M. fascicularis) by applying a laser to the trabecular meshwork to increase intraocular pressure (IOP). After other behavioral and electrophysiological studies, the lateral geniculate nuclei (LGNs) and the primary visual cortices were analyzed for functional afference from surviving ganglion cells, indicated by cytochrome oxidase (CO) histochemistry. RESULTS: CO reactivity (COR) indicated a general reduction in neural metabolism with increasing severity of glaucoma. COR in the LGNs was reduced to the same degree in both the P- and M-cellular layers. In layer 4Cbeta of the V1 cortex, the reactivity was always reduced more than in the layer 4Calpha division. CONCLUSIONS: Experimental glaucoma in monkeys reduces visual afference to the central nervous system, thereby reducing the metabolic drive as indicated by COR. The detrimental effect of glaucoma did not appear to be any greater for the M-cell, rather than the P-cell pathway in the LGN or in the visual cortex. Both are affected by the duration and severity of the experimental glaucoma. Overall, the alterations in metabolism of neurons in the parallel visual pathways supplied by the Palpha and Pbeta ganglion cells do not suggest that tests based on the functional properties of one or the other would provide optimal assessment of glaucoma.

Animals↗
PubMed1980

Perceptual signs of parallel pathways.

Previous physiological work has shown that the X and Y cells found in the visual pathways of cats and monkeys have properties that might explain the perceptual distinction between 'sustained' and 'transient' mechanisms. However, when the sensitivities of X and Y cells are measured under conditions comparable with those used in psychophysical experiments, one finds that the properties thought to be relevant to the perceptual dichotomy do not in fact distinguish the two types of cell. One of the most important psychophysical grounds for distinguishing 'sustained' from 'transient' mechanisms is that there appear to be two distinct thresholds for detecting grating patterns, depending upon whether the observer is asked to detect the spatial or the temporal properties of the stimulus. However, if threshold are measured under conditions where the observer's criterion is tigahtly controlled, the two thresholds converge. These experiments question the existence of qualitatively distinct 'sustained' and 'trasient' mechanisms.

Animals↗
PubMed1989

Neurological visual fields.

Neurological visual field defects represent lesions to the visual pathway, some of which may be life-threatening. It is, therefore, crucial that optometrists understand how to diagnose these lesions, so they may know when, and to whom to refer the patient. The following cases illustrate the management of patients with lesions to the prechiasmal, chiasmal, and postchiasmal visual pathway.

Adenoma, Chromophobe↗
PubMed1999

Diagnostic value of magnetic resonance imaging and planimetric measurement of optic disc size in confirming optic nerve hypoplasia.

PURPOSE: This study set out to evaluate magnetic resonance imaging (MRI) and measurement of optic disc size as diagnostic tools for confirming the diagnosis of optic nerve hypoplasia (ONH) in children with impaired growth. METHODS: MRI was performed to study the size of the intracranial visual pathways, and image analysis measurements of fundus photographs were performed to determine the size of the optic disc. Results from these investigations were compared with those using the gold standard for diagnosis of ONH, which was the clinical eye examination (visual function, ophthalmoscopic signs, or both). Forty children (median age, 9 years; range, 3 to 19 years) with impaired growth were included in the study. RESULTS: The prevalence of ONH among the children was 15%. MRI classification of the visual pathways had a higher positive predictive value than image analysis measurement of the optic disc size (1.0 vs 0.6). CONCLUSIONS: MRI is a good tool for confirming the diagnosis of ONH and may thus facilitate early detection. On the other hand, a small optic disc per se is not a definite indicator of ONH but should encourage further investigation with MRI, especially if there is a clinical suspicion of ONH.

Adolescent↗
PubMedDate not supplied

An integrated approach to the treatment of chiasmatic-hypothalamic gliomas.

The treatment of visual pathway gliomas is controversial. The many retrospective studies reporting outcome data for patients with chiasmatic/hypothalamic gliomas are difficult to interpret for several reasons. First the natural history of these tumors is erratic with some reports suggesting that most visual pathway gliomas are hamartomas and follow an indolent course, and others reporting 10-year survival rates of close to 60%. Second, earlier studies did not clearly indicate which patients had neurofibromatosis type 1 (NF1) and recent evidence suggests that the natural history of optic gliomas is more favorable in patients with NF1. Third the methods and accuracy of diagnosis have changed dramatically and patients diagnosed before and after the advent of CT/MR imaging have often been included in the same series. While surgical resection is usually not a viable option for definitive treatment of these tumors, recent studies have shown favorable results after subtotal resection in selected patients. The efficacy of radiotherapy has not been unequivocally demonstrated and treatment-related morbidity has become a major concern, in particular, adverse effects on cognition and growth. Chemotherapy has been advanced as an viable alternative to avoid or delay the adverse affects of RT, but the long-term outcome benefits and adverse effects of treatment are just being defined. Despite the limitations of currently available information, sufficient data are now available to rational management quotelines for the majority of children with chiasmatic/hypothalamic gliomas.

Antineoplastic Agents↗
PubMed2004

Interaction of top-down and bottom-up processing in the fast visual analysis of natural scenes.

The influence of task requirements on the fast visual processing of natural scenes was studied in 14 human subjects performing in alternation an "animal" categorization task and a single-photograph recognition task. Target photographs were randomly mixed with non-target images and flashed for only 20 ms. Subjects had to respond to targets within 1 s. Processing time for image-recognition was 30-40 ms shorter than for the categorization task, both for the fastest behavioral responses and for the latency at which event related potentials evoked by target and non-target stimuli started to diverge. The faster processing in image-recognition is shown to be due to the use of low-level cues, but source analysis produced evidence that, regardless of the task, the dipoles accounting for the differential activity had the same localization and orientation in the occipito-temporal cortex. We suggest that both tasks involve the same visual pathway and the same decisional brain area but because of the total predictability of the target in the image recognition task, the first wave of bottom-up feed-forward information is speeded up by top-down influences that might originate in the prefrontal cortex and preset lower levels of the visual pathway to the known target features.

Adult↗
PubMed1986

An assessment of decision-making as a possible factor in the age-related loss of contrast sensitivity.

The possibility that changes in decision-making may contribute to the age-related decline in contrast sensitivity has been investigated in nineteen young subjects (ages 21-38 years) and twenty-seven old subjects (ages 55-92 years). A signal detection paradigm was employed in which the detection of stationary sinusoidal grating patterns was measured at 3 and 15 cycles deg-1 for a range of contrasts which were psychophysically equivalent for each subject. A decline in contrast sensitivity with age at the spatial frequencies studied was confirmed for contrast thresholds obtained both by the ascending method and from the 50% hit rate for detection of the grating pattern. The criterion adopted for decision-making, expressed as both beta and percentage bias, did not change significantly between young and old subjects at 15 cycles deg-1. At 3 cycles deg-1, criterion beta did not change significantly at X0.8, X1.0, or X1.2 contrast threshold, but at contrast giving 50% hit rate there was a significant increase with age. The percentage bias increased significantly at contrast threshold but not at 50% hit rate. It is inferred from the results that the loss of contrast sensitivity was not accountable in terms of the adoption of a more conservative criterion by older subjects. Hence visual loss in ageing is attributed to changes within the visual pathway rather than within higher decision-making centres.

Adult↗
PubMed1979

[Visual evoked potential in multiple sclerosis].

Visual Evoked Responses (VER) by binocular flash stimulation were carried out in 30 cases of "definite" (15 cases-Group I) and of "probable" (15 cases-Group II) Multiple Sclerosis (MS). VER were recorded bilaterally by reference occiput-mastoid. Averaging of 50 responses (time base 200-500-1000 msec) was considered; measures were made by registration on X-Y Plotter. Abnormal VER by increased latencies of III and/or IV peak (Ciganek) were present uni- or bilaterally in most of the subjects (73,3% of the I Group; 66,6% of the II Group). Percentage of abnormal VER is quite higher than clinical involvement of visual pathways; it is present in 3 out of 5 patients also, in whom clinical findings were confined to spinal cord. The results are discussed with reference to the previous literature. Recording of VER seems useful in detecting involvement of visual pathways without clinical evidence.

Adult↗
PubMed1984

Eleven cases of sarcoidosis of the optic nerve.

Of 11 patients (eight women and three men, ranging in age from 16 to 48 years) who had sarcoidosis of the optic nerve that caused decreased visual acuity and visual field abnormalities, only two were known to have sarcoidosis at the time the visual impairment developed. Four patients had granulomas involving the optic nerve head, four had granulomatous inflammation of the orbital or intracranial optic nerve or chiasm, and three had retrobulbar neuritis. All 11 patients had histologically confirmed idiopathic noncaseating granulomatous inflammation and eight of the 11 had abnormalities compatible with sarcoidosis in chest roentgenograms. In the three patients in whom the serum level of angiotensin-converting enzyme was determined, it was increased in one and normal in the other two. Computed tomography of the anterior visual pathways was the single most useful neurodiagnostic study. Treatment with corticosteroids was beneficial in six of the 11 cases. These cases demonstrated that sarcoidosis should be included in the differential diagnosis of any inflammatory or compressive lesion involving the anterior visual pathways.

Adolescent↗
PubMed2003

Relay of visual information to the lateral geniculate nucleus and the visual cortex in albino ferrets.

The abnormal organization of the central visual pathways in the albino ferret has been characterized anatomically and physiologically. Recordings in dorsal lateral geniculate nucleus of the albino ferret show that lamina A1, which receives an aberrant projection from the contralateral eye, contains an extensive representation of the ipsilateral visual hemifield with receptive fields located up to 35 degrees from the vertical meridian. This is not the case in pigmented ferrets, for which the vast majority of units, activated through either the contralateral or ipsilateral eye, have receptive fields confined to the contralateral hemifield. The few fields found in the ipsilateral hemifield are driven through the contralateral eye and none is more than 10 degrees from the midline. Cortical topography was studied by making closely spaced electrode penetrations across the area 17/18 border. In pigmented animals, the reversal of topography at the border is characterized by units with receptive fields centered a few degrees into the ipsilateral hemifield. In 22 of 25 albinos, the "Boston" aberrant topography was found: the representation of the vertical meridian is within area 17, rather than at the area 17/18 border. Instead, at the area 17/18 border, there is a reversal in the topographic progression at up to 30 degrees into the ipsilateral hemifield. This pattern was most pronounced in the upper visual field. In agreement with the "Boston" physiology, injections of retrograde tracer made in area 17 usually label neurons in either lamina A or the part of lamina A1 that is aberrantly innervated by the contralateral eye. A column of labeled cells extending through all geniculate layers is rarely seen in albinos, although this is commonly the pattern in pigmented ferrets.

Action Potentials↗
PubMed2000

Induction of visual orientation modules in auditory cortex.

Modules of neurons sharing a common property are a basic organizational feature of mammalian sensory cortex. Primary visual cortex (V1) is characterized by orientation modules--groups of cells that share a preferred stimulus orientation--which are organized into a highly ordered orientation map. Here we show that in ferrets in which retinal projections are routed into the auditory pathway, visually responsive neurons in 'rewired' primary auditory cortex are also organized into orientation modules. The orientation tuning of neurons within these modules is comparable to the tuning of cells in V1 but the orientation map is less orderly. Horizontal connections in rewired cortex are more patchy and periodic than connections in normal auditory cortex, but less so than connections in V1. These data show that afferent activity has a profound influence on diverse components of cortical circuitry, including thalamocortical and local intracortical connections, which are involved in the generation of orientation tuning, and long-range horizontal connections, which are important in creating an orientation map.

Animals↗
PubMed1986

[Morphologic features of the chemosensory, visual and vestibular pathways of Helix lucorum].

The structure of chemosensory, visual and statocyst pathways of the snail Helix lucorum has been studied by means of five histological methods. The chemoreceptors of the optic tentacle bulb, small and large neurons of tentacle ganglion and bipolar cells of olfactory nerve send their processes to the CNS of the mollusc. In the CNS these processes divide into many clusters of branches. All protocerebral cells and the cluster of neurons of the commissural part of metacerebrum send their processes within the olfactory nerve towards the periphery. The axons of eye cells terminate in the enlargement of optic nerve near the eye; so do the CNS cells and neurons of the optic nerve. In the neuropile of pleural part of metacerebrum a region of ramification of cell axons of the visual pathway is found. Hair cells of statocyst send their axons within the static nerve to the cerebral ganglion (CG). Small cells of metacerebrum send their axons towards the statocyst. In the neuropile of ipsilateral CG some processes of statocyst pathway cells divide into many thin branches; others--cross to the contralateral cerebral neuropile via the commissure joining two CG. In the neuropile of contralateral ganglion these processes give off a spray of many branches just as in the ipsilateral ganglion. The axons of the visual pathway cells and statocyst pathway cells ramify in the same region.

Animals↗
PubMed1990

A polyclonal antibody to goldfish neuronal 145 kDa intermediate filament protein.

A polyclonal antibody raised to a protein from goldfish optic tectum recognises, immunohistochemically, axons throughout normal goldfish visual pathway. In goldfish with injured optic nerve, this antibody recognises degenerating neuronal debris as well as regenerating fibres. On immunoblot, the antibody recognises, primarily, a neuronal intermediate filament protein in the region of 145 kDa. Such an antibody should prove useful in studies pertaining to goldfish visual pathway.

Animals↗
PubMed1989

Normal and abnormal visual development in kittens: insights into the mechanisms that underlie visual perceptual development in humans.

For many years the mechanisms that underlie normal and abnormal development of visual perception in human infants have been explored in anatomical and physiological studies on two species of frontal-eyed mammals, namely, cats and, to a lesser extent, monkeys. The unstated assumption underlying the investigations on cats is that despite substantial differences in the organization of the visual pathways of cats and humans, as well as quantitative differences in their perceptual abilities, principles of development established in the former also apply to humans. This review examines the extent to which this assumption may be valid. Following a review of certain anatomical peculiarities of the cat visual system, several of the differences as well as the parallels between the perceptual abilities of cats and humans are summarized. The latter similarities, as well as the larger number of parallels between the two species that can be drawn during development, attest to the validity of the choice of the cat for study of the mechanisms that underlie human visual development.

Animals↗
PubMed1975

Direct visual input to the limbic system: crossed retinal projections to the nucleus anterodorsalis thalami in the tree shrew.

Evidence for a direct projection from the retina to the nucleus anterodorsalis thalami in the insectivore, Tupaia glis, is presented. 100 muCi tritiated amino acid or amino acid/monosaccharide cocktail were administered as two separate intravitreal injections of 50 muCi each. Fibers were traced using thawmount autoradiography in which tissue is frozen in liquid propane, cryostat-cut, and mounted on photographic emulsion precoated slides (Conrad and Stumpf, 1974). From the dorsolateral geniculate body, contralateral retinal fibers continue as a dorsomedial extension of the optic tract. When traced rostrally from this point, the fibers form a thin fascicle coursing medially under the third ventricle. In the anterior thalamus the bundle arborizes within the n. anterodorsalis, infiltrating its caudal pole completely but only encapsulating the nucleus anteriorly. This new retino-anterodorsal thalamic projection, together with the known anterior thalamic-retrosplenial projection, represents a third visual pathway in Tupaia glis distinct from the retino-geniculo-striatal and retino-tecto-pulvinar-peristriatal systems. It is significant that each of these thalamic relay nuclei projects to an architectonically different cortical region, with the nucleus anterodorsalis sending afferents to the phylogenetically most primitive of the visual cortices, the retrosplenial proisocortex or prostriata (Vitzthum and Sanides, 1967). It is proposed that the retino-anterior thalamic-retrosplenial circuit forms an anatomical substrate by which light cues may affect emotional behavior and corresponding neurovisceral responses.

Amino Acids↗
PubMed1983

Optics, the eye, and the brain.

Optics began as a visual science, and the eye was the original optical instrument. Students of physiological optics, together with their clinical colleagues, were concerned mainly with the normal and pathological functioning of the eye as a receptor organ. In recent years, however, exciting developments have changed all that. Optics has taken off in many directions that have little immediate relation to the eye, such as x-ray astronomy, lasers, and photoacoustic spectroscopy. Vision research, in turn, has gone far beyond its sole preoccupation with the optics of the eye. Most exciting are new discoveries about the visual pathways and the specialization of individual brain cells for the processing of line orientation, stereoscopic depth, spatial frequency, motion, and color. Comparative studies reveal the functional architecture of the brain together with the genetically and chemically programmed cellular development that lays the groundwork for later modification by the visual environment. Stimulated by this neurophysiological progress, and by newly available optical concepts and techniques, visual scientists have greatly expanded their research beyond the traditional topics of physiological optics and color.

Brain↗
PubMed1999

Recording and manipulating the in vivo correlational structure of neuronal activity during visual cortical development.

Many aspects of visual cortical functional architecture, such as orientation and ocular dominance columns, are present before animals have had any visual experience, indicating that the initial formation of cortical circuitry takes place without the influence of environmental cues. For this reason, it has been proposed that spontaneous activity within the developing visual pathway carries instructive information to guide the early establishment of cortical circuits. Recently developed recording and stimulation techniques are revealing new information about the in vivo organization of this spontaneous activity and its contribution to cortical development. Multielectrode recordings in the developing lateral geniculate nucleus (LGN) of ferrets demonstrate that retinal spontaneous activity is not simply relayed to the visual cortex, but is reshaped and transformed by a variety of mechanisms including cortical feedback and endogenous oscillatory activity. The resulting patterns are consistent with many of the predictions of correlation-based models of cortical development. In addition, the introduction of artificially correlated activity into the visual pathway disrupts some but not all aspects of orientation tuning development. Thus, while these results support an instructive role of spontaneous activity in shaping cortical development, there still appears to be a number of aspects of this process that cannot be accounted for by activity alone.

Animals↗