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PubMedDate not supplied

Changes in geniculate cell size following brief monocular blockade of retinal activity in kittens.

When a kitten is subjected to monocular lid suture early in life, cells in laminae of the lateral geniculate nucleus (LGN) connected to the sutured eye grow less than normal and cells in those laminae connected to the non-sutured eye grow more than normal. These changes are seen primarily in the binocular segment of the LGN, which corresponds to the central visual field, and are due to competition either between intracortical afferents originating from the different LGN laminae, or directly among cells within the LGN. The afferent deprivation induced by lid suture, however, is not complete, as retinal ganglion cells fire tonically both in darkness and in light. It is generally thought that this tonic retinal activity is necessary to maintain neuronal excitability at normal threshold in the central visual pathway. In the visual cortex of developing kittens, we previously showed a long-lasting change in ocular dominance of binocular cells by a brief blockade of retinal activity in one optic nerve. We report here that a complete blockade of retinal activity in one eye causes major changes in LGN cell size within 1 week. These changes occur throughout the LGN, including the monocular segment where binocular competition does not occur. The results indicate that tonic retinal activity may have an important role in the control of geniculate cell size.

Animals↗
PubMed2002

Seeing, since childhood, without ventral stream: a behavioural study.

We report the case of a 30-year-old man (S.B.) who developed visual agnosia following a meningoencephalitis at the age of 3 years. MRI disclosed extensive bilateral lesions of the occipital temporal visual pathway (ventral stream) and lesions in the right dorsal pathway, sparing primary visual cortices. S.B. showed a severe visual recognition deficit (texture, colour, objects, faces and words), although movement and space perception were largely preserved. His remaining visual capacities illustrate the competence of an isolated dorsal system which essentially functions on the sole basis of magnocellular afferents (low spatial resolution, high sensitivity to low contrast and moving stimuli). Patient S.B. also shows remarkable visuomotor competences, despite his perceptual limitations. It is suggested that his perceptual capacities correspond to the visual processing limitations of the dorsal visual stream, which in this patient have become accessible to perceptual awareness.

Adolescent↗
PubMed1999

Visual thalamotelencephalic pathways in the sturgeon Acipenser, a non-teleost actinopterygian fish.

Terrestrial vertebrates (amphibians, reptiles, birds, and mammals) possess two visual systems, the geniculate and extrageniculate pathways to the telencephalon. In cartilaginous fishes (e.g. sharks) both retinal and tectal neurons project to neurons in the thalamus, which themselves project to a single area in the telencephalon. The condition in ray-finned fishes (Actinopterygii) is ambiguous. In many teleosts there is a well developed extrageniculate pathway but no obvious geniculate system. This study reports on the thalamotelencephalic projections of a sturgeon, a non-teleost ray-finned fish. Several tract tracing methods (e.g., HRP, WGA-HRP, biocytin, BDA, DiI) were employed in conjunction with normal techniques for identifying neural structures (e.g., Nissl, Golgi). After injections of tracer into retinal and tectal recipient areas of the thalamus, labeled terminals were observed in the ventrolateral region of the caudal telencephalon, an area referred to as the thalamic projection area. After injections of tracer into the telencephalon, populations of retrogradely filled neurons were located in both the dorsal and ventral thalamus. These data demonstrate that thalamic neurons in both retinal and tectal pathways project directly to the telencephalon. These results support the view that two visual pathways are a primitive feature of vertebrate brain organization. These results are also consistent with the hypothesis that the ancestor of Acipenser and Teleostei (Actinopteri) acquired a novel visual pathway to the telencephalon through the ventral portion of the thalamus.

Animals↗
PubMed2002

Visualization of 'water secretion' by confocal microscopy in rat salivary glands: possible distinction of para- and transcellular pathway.

Visualization of water transport in cells, tissues and organs is an important, yet still difficult, task in morphological science. By using confocal microscopy and the fluid-phase fluorescent tracer technique, we visualized water secretion and estimated the routes of water transport across the acinar epithelia in rat parotid and submandibular glands. Confocal microscopy of whole glands perfused arterially with Lucifer yellow revealed a bright fluorescence at the basolateral space of acini. Luminal space was devoid of fluorescence, but revealed it after isoproterenol pretreatment, ductal infusion of fluorescent dextrans into the lumen, or tissue dissociation by collagenase. Under these conditions, stimulation of fluid secretion with carbachol caused a rapid decline of the luminal fluorescence intensity, indicating that the secreted water washed out the fluorescent probes in the acinar lumen. In the stimulated dissociated acini, the luminal fluorescence disappeared by 15 sec, but reappeared at 30-45 sec to maintain a low plateau level. By assuming that the tight junction was 'paralyzed' by the collagenase digestion and that the paracellular fluid transport could not influence the dilution of Lucifer yellow, we estimated that the initial water secretion by CCh occurs via the transcellular pathway, while later than 30-45 sec the additional water permeates through the paracellular pathway.

Algorithms↗
PubMed1990

Binocularity in the little owl, Athene noctua. I. Anatomical investigation of the thalamo-Wulst pathway.

The efferent projections from the visual thalamus to the Wulst were studied in the little owl, Athene noctua. Cells of origin were identified by retrograde labeling after injections of wheat-germ-agglutinin-conjugated horseradish peroxidase into the Wulst. The labeled-cell distribution was correlated with the distribution of anterogradely labeled retinal terminals as revealed by intraocular injections of horseradish peroxidase. The results demonstrated a bilateral thalamofugal visual pathway ascending from the nucleus dorsolateralis anterior thalami (DLA). Projections from the visual thalamus to the Wulst showed a specific and orderly pattern, and retrogradely labeled cells of DLA were distributed equally, in a complementary fashion, on both sides of the brain, with a small region of overlap. Retinal termination fields in DLA largely overlapped relay neurons projecting to either Wulst, although the overlap was not complete. Despite differences in the organization of avian and mammalian visual pathways, which reflect their separate evolutionary origins, similarities between the DLA in the little owl and the lateral geniculate nucleus in mammals suggest that, during evolution similar selective pressures for binocularity led to a similar morphological organization.

Animals↗
PubMed1999

[Controversies and current status of therapy of optic nerve damage in craniofacial traumatology and surgery].

In craniomaxillofacial traumatology, surgical oncology and craniomaxillofacial reconstruction, a surgeon's aim may interfere with the prechiasmatic visual pathway. Precise concepts and therapeutic strategies are mandatory to detect and deal with anterior visual pathway disorders. In order to develop these strategies, knowledge of the pathomechanisms of potential optic nerve trauma, primary radiological investigations, and further diagnostic measures are important. Due to the difficulties in neuroophthalmological testing of visual pathway functioning in severely injured patients or even during craniomaxillofacial reconstructions, we established flash-evoked visual potentials (VEP) and the electroretinogram (ERG) as reliable electrophysiological methods to gather specific information as to whether the visual pathway function is intact, even if pathological, but still present or absent. Case reports show that subjectively or objectively confirmed unilateral amaurosis does not necessarily mean irreversible vision loss. The electrophysiological evaluation together with multiplanar computer tomography (CT) are important for the immediate identification of optic nerve trauma. The results of this evaluation will provide the diagnostic information on whether surgical intervention and/or conservative therapy is required to prevent secondary optic nerve damage. The conservative therapy of choice for the treatment of traumatic optic nerve lesions is the methylprednisolone-megadosis regimen (30 mg Urbason/kg bodyweight i.v. and 5.4 mg/kg bodyweight/h i.v. for the following 47 h). Surgical therapy involves decompression of the orbital compartment in case of retrobulbar hematoma or decompression of the intracanalicular part of the optic nerve in the traumatized optic canal or posterior orbit as confirmed by CT. Prospective analysis of our trauma patients and the international literature on traumatic optic nerve lesions show that the time factor in when to start therapy has been greatly underestimated. To fulfill modern treatment concepts in craniomaxillofacial surgery, sound diagnostic and therapeutic knowledge on the maintenance of visual pathway function is required.

Adolescent↗
PubMed1991

[Phosphenes elicited by subcortical stimulation in man].

Electrical stimulation of a point in the visual pathway can evoke a visual sensation which is called a phosphene. The phosphenes elicited by intracerebral stimulation were investigated in twenty-three subjects. One hundred and seven phosphenes were reported and all of them appeared in the visual field contralateral to the side of stimulation. The exception was a single case where a diffuse flashing sensation appeared in the whole visual field. Thirteen patients reported white phosphenes and nine patients reported coloured phosphenes. In the medial area (10-15 mm from the midline) of the occipital lobe, stimuli above the calcarine fissure resulted in phosphenes in the lower quadrant of the visual field. In the lateral area (16-32 mm from the midline), however, stimuli above the level of the calcarine fissure tended to produce phosphenes in the upper quadrant. These findings appear to conflict with traditional concept of the physiological anatomy of the visual pathway in man. The possible mechanism of this phenomenon produced by intracerebral stimulation is discussed in relation to the phosphenes produced by cortical stimulation.

Adult↗
PubMed1981

[Diagnosis and differential diagnosis of hysteric amblyopia using psychophysical and electro-ophthalmological examination methods (author's transl)].

In three patients with psychogenic amblyopia the computerized visual field, the ERG, the flash light (H-EP) and pattern reversal stimulated (M-EP) cortical potentials were recorded. Differential diagnosis between psychogenic amblyopia on the one hand, and functional amblyopia and organic lesions of the retrobulbar visual pathways on the other was shown to be possible. In the cases with organic retrobulbar lesions of visual pathways, visual field defects and pathologic H-EP's and M-EP's were found. In functional amblyopia only the M-EP responses are diminished in amplitude. In psychogenic amblyopia only the computerized visual field shows pathologic changes.

Adolescent↗
PubMed2006

[Parallel processing of visual information].

This is a survey on the function of parallel visual pathway with a special emphasis on its clinical implications. It is based on data in the literature and own results of our group. The paper primarily deals with the X, Y, W pathways and by the magnocellular, parvocellular and koniocellular visual pathways characterized by cells of various size as well as by nerve fibers of various thickness. Electrophysiological, microelectrode recording of single-unit activity makes the distinction between the pathways available in animal model. Much more difficulties arise if we intend to characterize the pathways in humans or to detect the selective damage of one of these pathways in patients. The non-invasive diagnostic methods that could be used in the diagnosis are detailed here, too. Finally, the neurological, ophthalmological and psychological diseases are discussed in which a selective damage of any visual pathway is suspected. Summing it up, the survey provides evidences for the introduction of the novel concept of parallel pathways into the diagnostic aspects of ophthalmology, neurology and psychiatry.

Humans↗
PubMed1983

Low-contrast letter charts as a test of visual function.

Visual pathway disorders can cause visual loss that is not detected by the Snellen test: visual sensitivity to coarse detail may be depressed, even when visual sensitivity to fine detail is unaffected. Sinewave grating test targets can detect such hidden visual loss. However, electronic apparatus for generating sinewave gratings is expensive, while the inexpensive Arden plates provide no check on the patient's accuracy. We have tested 10 patients and 10 control subjects with a set of five letter charts (including the standard Snellen chart). These letter charts were of different contrasts, namely 10%, 22%, 31%, 64% and 93%, but otherwise were substantially alike. Subjects were also tested with sinewave gratings. We found good agreement between sinewave grating and letter chart findings. In particular, the charts picked up visual loss that was not detected by the standard Snellen chart: they detected visual pathway dysfunction in all seven patients whose sinewave data were abnormal. Our findings suggest that even one low-contrast letter chart could provide a valuable supplement to the standard Snellen chart. Compared with other available devices, these charts have the advantages of cheapness, simplicity and of providing the ophthalmologist with an immediate check on patients' accuracy.

Adult↗
PubMed2006

Snakes as agents of evolutionary change in primate brains.

Current hypotheses that use visually guided reaching and grasping to explain orbital convergence, visual specialization, and brain expansion in primates are open to question now that neurological evidence reveals no correlation between orbital convergence and the visual pathway in the brain that is associated with reaching and grasping. An alternative hypothesis proposed here posits that snakes were ultimately responsible for these defining primate characteristics. Snakes have a long, shared evolutionary existence with crown-group placental mammals and were likely to have been their first predators. Mammals are conservative in the structures of the brain that are involved in vigilance, fear, and learning and memory associated with fearful stimuli, e.g., predators. Some of these areas have expanded in primates and are more strongly connected to visual systems. However, primates vary in the extent of brain expansion. This variation is coincident with variation in evolutionary co-existence with the more recently evolved venomous snakes. Malagasy prosimians have never co-existed with venomous snakes, New World monkeys (platyrrhines) have had interrupted co-existence with venomous snakes, and Old World monkeys and apes (catarrhines) have had continuous co-existence with venomous snakes. The koniocellular visual pathway, arising from the retina and connecting to the lateral geniculate nucleus, the superior colliculus, and the pulvinar, has expanded along with the parvocellular pathway, a visual pathway that is involved with color and object recognition. I suggest that expansion of these pathways co-occurred, with the koniocellular pathway being crucially involved (among other tasks) in pre-attentional visual detection of fearful stimuli, including snakes, and the parvocellular pathway being involved (among other tasks) in protecting the brain from increasingly greater metabolic demands to evolve the neural capacity to detect such stimuli quickly. A diet that included fruits or nectar (though not to the exclusion of arthropods), which provided sugars as a neuroprotectant, may have been a required preadaptation for the expansion of such metabolically active brains. Taxonomic differences in evolutionary exposure to venomous snakes are associated with similar taxonomic differences in rates of evolution in cytochrome oxidase genes and in the metabolic activity of cytochrome oxidase proteins in at least some visual areas in the brains of primates. Raptors that specialize in eating snakes have larger eyes and greater binocularity than more generalized raptors, and provide non-mammalian models for snakes as a selective pressure on primate visual systems. These models, along with evidence from paleobiogeography, neuroscience, ecology, behavior, and immunology, suggest that the evolutionary arms race begun by constrictors early in mammalian evolution continued with venomous snakes. Whereas other mammals responded by evolving physiological resistance to snake venoms, anthropoids responded by enhancing their ability to detect snakes visually before the strike.

Animals↗
PubMed1992

Visual evoked potentials in infants and children.

Visual evoked potential (VEP) studies are of great value in a wide variety of pediatric patients, including those with disorders of the sensory visual pathway and those at risk for visual pathway damage. VEPs are simple, non-invasive, and are particularly appropriate for infants and young children who cannot communicate visual symptoms or cooperate for standard vision assessment. VEPs in pediatric patients have the following main purposes: (1) detecting lesions causing dysfunction of the sensory visual pathways (the VEP is a sensitive indicator of subclinical lesions and can be used to differentiate visual impairment from visual inattention in young infants); (2) confirming functional loss when disorders of the visual system are present; (3) quantifying visual impairment in patients with known visual disorders, accomplished either empirically by noting the severity of the VEP abnormality to flash and pattern stimuli or by visual acuity estimation studies (early quantification of vision loss allows referral to early intervention programs, which can ameliorate the long-term consequences of the disability); (4) monitoring patients who are at risk for visual complications either from diseases (such as hydrocephalus or neurofibromatosis) or as a complication of therapeutic intervention (e.g., neurosurgery, chemotherapy) to help detect and avoid long-term sequelae of such therapies on the developing nervous system; (5) establishing prognosis for visual and systemic recovery based on flash VEPs for specific pediatric disorders including perinatal asphyxia in full-term neonates, acute-onset cortical blindness, and, to a fair extent, in comatose children; and (6) in some cases, contributing to the differential diagnosis. Abnormalities of flash and/or pattern VEPs are generally nonspecific to the type of exact location of the lesion, except in distinguishing prefrom postchiasmal lesions. However, in certain conditions, such as the hereditary ataxias of childhood, VEP abnormalities may help in the diagnosis. Similarly, deterioration in VEPs may help differentiate progressive from static encephalopathies. VEPs have become an indispensable tool in pediatric ophthalmology and neurology. They will probably play an increasingly important role in the future, primarily due to the difficulty in assessing visual system function in young or ill children and the VEP's sensitivity to subclinical damage in this aspect of the central nervous system.

Brain Damage, Chronic↗
PubMed1992

Visual field defects in vascular lesions of the lateral geniculate body.

Corresponding retinal nerve fibres begin their path in the eyes and end in a single visual cortical cell. Because of this arrangement, lesions in the anterior visual pathway produce incongruent visual field defects and in the posterior pathway congruent field defects. The lateral geniculate body is on the anterior third of the visual pathway. A lesion of this nucleus produces moderately to completely congruent visual field defects. Five patients with ischaemic lesions of the lateral geniculate body are reported. Two patients had a wedge-shaped homonymous hemianopia, two other cases had congruent superior homonymous quadratic defects and the fifth a quadruple sector defect. The lateral geniculate body has a dual blood supply from the anterior choroidal artery (branch from internal carotid artery) and from the lateral choroidal artery (branch from the posterior cerebral artery). A schematic diagram has been devised which shows that a knowledge of the visual field disrupted can identify the arterial system involved.

Aged↗
PubMed1999

Neurochemical gradients along monkey sensory cortical pathways: calbindin-immunoreactive pyramidal neurons in layers II and III.

We examined the distribution of neurons containing immunoreactivity for three calcium-binding proteins, calbindin, parvalbumin and calretinin, as well as nonphosphorylated neurofilament protein, in cortical areas along the ventral and dorsal cortical visual pathways, and in ventrally-directed somatosensory and auditory cortical pathways. Calbindin-immunoreactive pyramidal neurons showed the most prominent regional differences. They were largely restricted to layers II and III and their number monotonically increased from the primary sensory areas to the anteroventral areas along the ventral visual pathway and along the ventrally-directed somatosensory and auditory pathways. The number of calbindin-immunoreactive pyramidal neurons in layers II and III also increased along the dorsal visual pathway, but the number in the last recognized stage of the dorsal visual pathway (area 7a) was significantly smaller than that at the corresponding stage in the ventral visual pathway (TE). The number of calbindin-immunoreactive pyramidal neurons was highest in layers II and III of areas 35/36, TG, and TF/TH, which represent terminal cortical regions of the pathways. These results show neurochemical differences between cortical areas located at early and late stages along serial corticocortical pathways, as well as confirming differences between pyramidal neurons in the supragranular and infragranular layers.

Animals↗
PubMed1995

Development of metabolic response in male quail brain during sexual maturation.

Seasonal reproductive activities of Japanese quail Coturnix japonica are induced most obviously by stimulatory effects of long-day photoperiod. This study addressed the metabolic response, as measured by 2-deoxyglucose (2-DG), in brain of male quail during sexual maturation. At 7 weeks of age, reproductively quiescent quail exposed to a short photoperiod of 6L:18D, received 2-DG on day 0 and +3, +6, +9, +12, +15 and +18 days after onset of 16L:8D. Brains were processed for autoradiography; serum testosterone was measured to indicate reproductive response to photoperiod. Circulating testosterone remained low until day 9, then rose sharply, reaching maximum levels at day 18. Heavily labeled nuclei were identified in some discrete neural pathways: both tectofugal and thalamofugal visual pathways, ascending auditory pathway, efferent vocalization pathway, and limbic structures. Metabolic activity of the terminal nucleus (ectostriatum) of the tectofugal pathway increased significantly by day 18, but in the terminal nuclei (the Wulst) of the thalamofugal visual pathway activity did not change significantly. Energy metabolism of some nuclei of the auditory pathway rose significantly by day 3, although in the vocal pathway it did not show augmentation until days 15-18. The metabolic activity of limbic structures also increased. These results suggest that, in Japanese quail, sensory nuclei and some of their integrative areas become sensitive to environmental cues in response to long-day photoperiod. It is possible that the external environmental cues that affect the reproductive activities of quail act through sensory systems.

Animals↗
PubMed1988

The nasotemporal division in primate retina: the neural bases of macular sparing and splitting.

In primates, each hemisphere contains a representation of the contralateral visual hemifield; unilateral damage to the visual pathways results in loss of vision in half of the visual field. Apparently similar severe, unilateral lesions to the central visual pathways can result in two qualitatively different central visual field defects termed macular sparing and macular splitting. In macular sparing a 2 degrees to 3 degrees region around the fovea is spared from the effects of unilateral damage to the visual pathways. In macular splitting there is no such spared region and the scotoma produced by unilateral brain damage bisects the fovea. The patterns of decussation of the different classes of retinal ganglion cells in both New World (Saimiri sciureus) and Old World (Macaca fascicularis) monkeys have been determined by horseradish peroxidase injection. In both species the distributions of ipsilaterally and contralaterally projecting ganglion cells in the central retina are different from those in other mammals and suggest neural bases for macular sparing and splitting, respectively.

Animals↗
PubMed2006

Visual restoration in cortical blindness: insights from natural and TMS-induced blindsight.

Unilateral damage to visual cortex of the parietal or occipital lobe can cause the patient to be unaware of contralesional visual information due to either hemispatial neglect or hemianopia. It is now known that both neglect and hemianopia result from the disruption of a dynamic interaction between cortical visual pathways and more phylogenetically primitive visual pathways to the midbrain. We consider the therapeutic implications of these cortical-subcortical interactions in the rehabilitation of hemianopia. We start with the pheonmenon of "blindsight", in which patients with hemianopia can be shown, by implicit measures of visual detection or discrimination, to process visual information without conscious awareness. Some variants of blindsight have been postulated to recruit subcortical processes, while others may reflect compensatory optimisation of processing of spared visual cortex. Both mechanisms may offer opportunities for innovative strategies for rehabilitation of visual field defects. We relate the neural mechanisms that have been proposed to underlie blindsight to those that have been suggested to underlie the recovery of visual function after rehabilitation. It is suggested that the similarity and overlap of the neural processes supporting blindsight and recovery of visual function might provide insights for effective rehabilitation strategies for restoring visual functions.

Animals↗
PubMed1983

Apparent discrepancy between single-unit activity and [14C]deoxyglucose labeling in optic tectum of the rattlesnake.

Autoradiographic analysis of [1-14C]2-deoxy-D-glucose-6-phosphate ([14C]2-DG-P) accumulation in the rattlesnake brain stem and optic tectum was used in an effort to map infrared and visual neuronal pathways. Visual stimulation with a standard stimulus (a heat lamp) resulted in dense labeling of the superficial layers of the optic tectum. Infrared stimulation with the same standard stimulus resulted in labeling at the first synaptic relay, the lateral descending nucleus of the trigeminal tract (LDN-V), but not at higher levels, including the optic tectum. Systematic comparison of electrophysiological properties of tectal neurons was performed using the standard stimulus. Responses of infrared units in one hemitectum and visual units in the other, elicited by the same stimulus used in the [14C]2-DG-P experiments, were analyzed. There were no clear differences in the number, maximal density, spread, or rates of accommodation of visual units and infrared units, although the locus of maximal density was more superficial for visual units. In general, infrared units generated a greater number of action potentials than did visual units. All infrared units responded only to onset of the stimulus but they varied greatly in their ability to maintain discharge for the full duration of the stimulus. Most visual units exhibited on-, off-, or on-off responses. Four units showed only inhibition of spontaneous activity during the visual stimulation. There were significant differences in the evoked responses elicited by visual and infrared stimulation in response to the standard stimulus. Infrared stimuli generated single, large, triphasic on-responses, whereas visual stimulation generated complex multiphasic and long-lasting on- and off-responses. The major infrared on peak reached maximal amplitude at greater depths and was larger than the major visual on peak. Amplitude of the infrared peak fell off more rapidly with distance from the locus of its maximum than did amplitude of the visual peak. These observations are consistent with the view that infrared stimulation is effective in discharging neurons but is not associated with intense synaptic excitation. In contrast, visual stimulation apparently does produce intense synaptic activity, as suggested by the duration, complexity, and spread of the visual evoked response. Failure of this synaptic activity to produce more spikes in visual units probably reflects either depolarizing spike inactivation or the admixture of excitatory and inhibitory actions. Our observations suggest that 2-deoxy-D-glucose uptake is not necessarily correlated with the degree of action potential activation of specific neuronal pathways. The amount of [14C]2-DG-P labeling may reflect the metabolic requirements for support of synaptic depolarization as well as that supporting action potentials.

Animals↗