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PubMed1999

Altered midline axon pathways and ectopic neurons in the developing hypothalamus of netrin-1- and DCC-deficient mice.

Optic nerve formation in mouse involves interactions between netrin-1 at the optic disk and the netrin-1 receptor DCC (deleted in colorectal cancer) expressed on retinal ganglion cell (RGC) axons. Deficiency in either protein causes RGC pathfinding defects at the disk leading to optic nerve hypoplasia (). Here we show that further along the visual pathway, RGC axons in netrin-1- or DCC-deficient mice grow in unusually angular trajectories within the ventral hypothalamus. In heterozygous Sey(neu) mice that also have a small optic nerve, RGC axon trajectories appear normal, indicating that the altered RGC axon trajectories in netrin-1 and DCC mutants are not secondarily caused by optic nerve hypoplasia. Intrinsic hypothalamic patterning is also affected in netrin-1 and DCC mutants, including a severe reduction in the posterior axon projections of gonadotropin-releasing hormone neurons. In addition to axon pathway defects, antidiuretic hormone and oxytocin neurons are found ectopically in the ventromedial hypothalamus, apparently no longer confined to the supraoptic nucleus in mutants. In summary, netrin-1 and DCC, presumably via direct interactions, govern both axon pathway formation and neuronal position during hypothalamic development, and loss of netrin-1 or DCC function affects both visual and neuroendocrine systems. Netrin protein localization also indicates that unlike in more caudal CNS, guidance about the hypothalamic ventral midline does not require midline expression of netrin.

Adrenocorticotropic Hormone↗
PubMedDate not supplied

Glioma of the anterior optic pathways.

A 10-month-old girl presented with visual loss in the right eye associated with bilateral optic atrophy. The suggestive clinical diagnosis was an optic nerve glioma. The computerized tomographic findings were unusual in that symmetric bilateral involvement of the anterior visual pathways were present. The radiological diagnosis of an optic glioma was histologically confirmed.

Cranial Nerve Neoplasms↗
PubMed2005

Velocity constancy and models for wide-field visual motion detection in insects.

The tangential neurons in the lobula plate region of the flies are known to respond to visual motion across broad receptive fields in visual space. When intracellular recordings are made from tangential neurons while the intact animal is stimulated visually with moving natural imagery,we find that neural response depends upon speed of motion but is nearly invariant with respect to variations in natural scenery. We refer to this invariance as velocity constancy. It is remarkable because natural scenes, in spite of similarities in spatial structure, vary considerably in contrast, and contrast dependence is a feature of neurons in the early visual pathway as well as of most models for the elementary operations of visual motion detection. Thus, we expect that operations must be present in the processing pathway that reduce contrast dependence in order to approximate velocity constancy. We consider models for such operations, including spatial filtering, motion adaptation, saturating nonlinearities, and nonlinear spatial integration by the tangential neurons themselves, and evaluate their effects in simulations of a tangential neuron and precursor processing in response to animated natural imagery. We conclude that all such features reduce interscene variance in response, but that the model system does not approach velocity constancy as closely as the biological tangential cell.

Animals↗
PubMed1982

Reduction in numbers of large ganglion cells in cat retina following intravitreous injection of antibodies.

Antibodies were prepared against large ganglion cells isolated from bovine retina and injected into the vitreous chamber of 1 eye in 6 adult cats. The other eye of each cat received either a control pre-immune gamma-globulin injection or was untreated. After a survival time of 9-86 days, ganglion cell density was assessed from Nissl-stained retinal whole-mounts. In each cat, there were fewer large ganglion cells (alpha-cells) in the immunoglobulin-injected retina than in the control retina. The reduction in large ganglion cells occurred in patches adjacent to areas of approximately normal large ganglion cell density. Counts of the number of large ganglion cells in both eyes of the 6 cats indicated that the immunoglobulin injected eyes had from 8% to 61% (mean 32%) fewer large ganglion cells than the paired control eyes. This was significantly greater than the difference in the number of large ganglion cells between pairs of normal or control-injected eyes. The magnitude of the effect was not related to the survival time following the immunoglobulin injection. Cell size measures of all ganglion cells in selected areas of retina indicated that the small ganglion cells were unaffected by the antibodies. However, there was a suggestion that the largest of the medium size ganglion cells were affected in addition to the large ganglion cells. Counts of total ganglion cells per unit area in affected regions of retina revealed a reduced overall density, suggesting that the ganglion cells were lost rather than decreased in size. These results indicate that antibodies to the large ganglion cells can be used to reduce the number of large ganglion cells (alpha-cells) in the cat retina. Since these cells correspond to the Y-cell functional class of ganglion cells in the cat retina, the antibodies may provide a useful tool for studying Y-cell function in the visual pathways.

Animals↗
PubMed2002

Symmetry detection and visual attention: a "binary-map" hypothesis.

Recent research suggests that human symmetry-detection mechanisms cannot simultaneously compare different colors across the axis of symmetry (Nature 399 (1999) 115). In the present study, observers were required to judge symmetry in arrays composed of elements varying not only in color, but also in size, spatial frequency and orientation. In every case, response times increased with the number of different levels of a given feature. It is proposed that this increase reflects a sequential strategy whereby coarse "binary maps" are created by attentional filtering, and the symmetry of each map is then checked. Experiment 2 required observers to detect "pseudo-symmetry" (symmetry in feature values defined relative to an arbitrary featural boundary); the ease with which this task was accomplished supported the binary map hypothesis. The results suggest that (1) symmetry detection is spatially imprecise, and (2) attentional gating can operate prior to symmetry detection in the visual pathway.

Adult↗
PubMed1990

Intact "biological motion" and "structure from motion" perception in a patient with impaired motion mechanisms: a case study.

A series of psychophysical tests examining early and later aspects of image-motion processing were conducted in a patient with bilateral lesions involving the posterior visual pathways, affecting the lateral parietal-temporal-occipital cortex and the underlying white matter (as shown by magnetic resonance imaging studies and confirmed by neuro-ophthalmological and neuropsychological examinations). Visual acuity, form discrimination, color, and contrast-sensitivity discrimination were normal whereas spatial localization, line bisection, depth, and binocular stereopsis were severely impaired. Performance on early motion tasks was very poor. These include seeing coherent motion in random noise (Newsome & Paré, 1988), speed discrimination, and seeing two-dimensional form from relative speed of motion. However, on higher-order motion tasks the patient was able to identify actions from the evolving pattern of dots placed at the joints of a human actor (Johansson, 1973) as well as discriminating three-dimensional structure of a cylinder from motion in a dynamic random-dot field. The pattern of these results is at odds with the hypothesis that precise metrical comparison of early motion measurements is necessary for higher-order "structure from motion" tasks.

Cerebral Cortex↗
PubMed1990

Visual telencephalon modulates directional selectivity of accessory optic neurons in pigeons.

The directional selectivity of units within the nucleus of the basal optic root (nBOR) of the accessory optic system (AOS) was studied before and after lesions of the visual telencephalon (visual Wulst) in urethane-anesthetized pigeons. In intact pigeons, most nBOR units preferred upward motion with a temporal component or downward motion with a nasal component. The ipsilateral and bilateral telencephalic lesions generated a dramatic reduction in the number of cells with optimal responses to upward motion. The overall distribution of preferred directions was still bimodal following ipsilateral or bilateral Wulst lesions, with most units showing best responses to a straight temporal or to downward-nasal directions. The contralateral Wulst lesions produced, instead, a marked reduction in downward preferences. The nBOR units which were studied in these cases showed mainly upward-temporal and upward-nasal responses. These data suggest an involvement of the visual Wulst in the determination of the directional selectivity of nBOR neurons in the pigeon. Specifically, the responses of nBOR units to upward motion appeared to depend on the integrity of the telencephalic descending systems which impinge, in both direct and indirect ways, upon that AOS nucleus. Taken together with data for the mammalian AOS, the present results indicate that nonretinal afferents to AOS nuclei have an important role in the functional organization of that subcortical visual pathway.

Animals↗
PubMed1999

Intraretinal axon diameter: a single cell analysis in the marmoset (Callithrix jacchus).

We have labelled individual retinal ganglion cells of a New World primate, the common marmoset (Callithrix jacchus) with neurobiotin and then measured axon, soma and dendritic field diameter. A total of 111 cells were analysed (62 parasol cells, 22 midget cells, 16 hedge cells and 11 small bistratified cells). When all retinal ganglion cells were grouped together axon diameter was positively correlated to soma diameter. When analysed according to cell class only midget cells showed a positive correlation between soma size and mean axon diameter. Dendritic field diameter and mean axon diameter of both parasol and midget cells showed significant correlations. Axon diameter is not constant along the intraretinal length of the axon and the rate of change in diameter appears to be related to the cell class and the initial size of the axon. Midget cell axons showed a rapid increase of up to 20% over the first 200 microm in contrast to parasol cell axons which increased more slowly over this distance but then showed a marked increase in diameter of up to 40% over the next 450 microm. However, axon diameter did not remain at these increased diameters but decreased at greater distances from the soma. The degree to which an axon changes its diameter is related to retinal ganglion cell class and the initial size of the axon. We postulate that these variations in intraretinal axon diameter may have a direct influence on conduction velocity and reflect a compensatory mechanism to minimise spatiotemporal dispersion along the visual pathway.

Animals↗
PubMed1998

A crossed projection from the optic tectum to craniocervical premotor areas in the brainstem reticular formation. An anterograde and retrograde tracing study in the mallard (Anas platyrhynchos L.).

The optic tectum in birds receives visual information from the contralateral retina. This information is passed through to other brain areas via the deep layers of the optic tectum. In the present study the crossed tectobulbar pathway is described in detail. This pathway forms the connection between the optic tectum and the premotor area of craniocervical muscles in the contralateral paramedian reticular formation. It originates predominantly from neurons in the ventromedial part of stratum griseum centrale and to a lesser extent from stratum album centrale. The fibers leave the tectum as a horizontal fiber bundle, and cross the midline through the caudal radix oculomotorius and rostral nucleus oculomotorius. On the contralateral side fibers turn to ventral and descend caudally in the contralateral paramedian reticular formation to the level of the obex. Labeled terminals are found in the ipsilateral medial mesencephalic reticular formation lateral to the radix and motor nucleus of the oculomotor nerve, and in the contralateral paramedian reticular formation, along the descending tract. Neurons in the medial mesencephalic reticular formation in turn project to the paramedian reticular formation. Through the crossed tectobulbar pathway visual information can influence the activity of craniocervical muscles via reticular premotor neurons.

Animals↗
PubMed2006

A simple account of cyclopean edge responses in macaque v2.

It has been shown recently that neurons in V2 respond selectively to the edges of figures defined only by disparity (cyclopean edges). These responses are orientation selective, often preferring similar orientations for cyclopean and luminance contours, suggesting that they may support a cue-invariant representation of contours. Here, we investigate the extent to which processing of purely local visual information (in the vicinity of the receptive field) might explain such results, using the most impoverished stimulus possible containing a cyclopean edge (a circular patch of random dots divided into two regions by a single edge). Many V2 cells responded better to the cyclopean edge than to uniform disparities, and most of these were at least broadly selective for the orientation of the cyclopean edge. Two characteristics argue against a cue-invariant contour representation: (1) the cyclopean edge response was frequently abolished by small changes to the component disparities; and (2) although V2 cells frequently responded to both signs of a cyclopean edge (defined by which side of the edge is in front), they did so at different edge locations. These characteristics are consistent with a simple feedforward scheme in which V2 neurons receive inputs from several V1 subunits with different disparity selectivity. We also found a correlation between the preferred orientations for cyclopean edges and contrast stimuli, suggesting that this feedforward wiring is not random. These characteristics suggest that V2 responses to cyclopean edges may be useful in supporting a cue-invariant contour representation higher in the visual pathway.

Animals↗
PubMed1984

A light-emitting diode array globe protector photostimulator.

Intraoperative visual-evoked potential recording has been a potentially useful procedure for monitoring the functional status of the visual pathways during certain neurosurgical procedures. Technical problems have limited its adoption. We report a light-emitting diode array globe protector photostimulator which enhances the stimulation component of the visual-evoked potential recording technique.

Brain Diseases↗
PubMed1981

Evidence for the existence of a retino-hypothalamo-retinal loop in rabbits.

Rabbits which have previously been exposed to 24-h light/dark alternations exhibit in their photic responses at all levels of the visual pathway, and in the electroretinogram, simultaneous circadian changes with a time course that is programmed by the preceding light/dark schedule. The occurrence of simultaneous changes in the response of the visual cortex to electrical stimulation at subcortical levels could not be established. After bilateral sectioning of the optic nerves, there were still changes in the electroretinogram which were now no longer programmed, but reflected the existence of a free-running rhythm. Bilateral sectioning of the cervical sympathetic nerves resulted in a complete absence of circadian changes in photic responses. The results suggest the possible existence of a retino-hypothalamo-retinal loop by means of which the responses to photic stimuli on a given day are modulated according to the time course of the light/dark alternations on the immediately preceding day. The possible role of this feedback loop in the origin of animal photoperiodism is discussed.

Animals↗
PubMedDate not supplied

Pupil in clinical diagnosis. Light reflex anatomy and the afferent pupil defect.

The neuroanatomy for the light reflex has been reviewed. The importance of the semidecussation of visual pathways in the afferent portion of the system has been emphasized. The anatomy of the near synkinesis and its relation to the anatomy of the light reflex have been reviewed. The various abnormalities of sensory pupil function have been outlined. Particular stress has been placed on the value of the afferent pupil defect in the diagnosis of sensory lesions affecting the eye because of retinal or optic nerve disease. In addition, the value of the consensual pupil in the diagnosis of afferent defects has received special comment.

Accommodation, Ocular↗
PubMed1987

[Demonstration of a retino-thalamo-hippocampal pathway in the rat].

Investigations using double labeling by axonal transport of tracers have shown that in the rat, four nuclei of the anterior thalamus (anterior dorsal, anterior ventral, lateral anterior, bed nucleus of the stria terminalis) that project to the CA1 region of the hippocampus also receive a discrete input from the contralateral eye. The significance of this telencephalic visual pathway is discussed in a phylogenetic context.

Afferent Pathways↗
PubMedDate not supplied

[Statistical analysis of interneuronal functional connections during conditioned reflex elaboration].

A milk conditioned reflex to a low frequency electrical stimulation of the visual pathways was elaborated in cats. Multineuronal activity in the visual and sensorimotor cortical areas was recorded in the chronic experiment. Statistical analysis of interneuronal intraanalyser and interanalyzer connections was made by constructing crosscorrelograms on the "Plurimat-C" computer. Comparison of the results of the interneuronal interaction in untrained and trained cats has shown an increase of one-way and two-way connections of both the intraanalyser and interanalyser types. Neurones with medium amplitude spikes changed their net properties more than other units acquiring ingoing and outgoing connections in both studied areas of the learned animals. Acquisition was achieved in all the neurones mainly due to increased number of connections from the sensorimotor analyser to the visual one. The problems of formation of backward conditioned connections and "local" conditioned reflex are discussed.

Animals↗
PubMed1986

Hemifield pattern-reversal visual evoked potentials (VEPs) in retrochiasmal lesions with homonymous visual field defect.

This study was designed to examine the clinical significance and the reliability of hemifield pattern reversal VEPs in the assessment of homonymous visual field defects due to retrochiasmal lesions. 13 patients with traumatic, neoplastic or ischemic lesions of the cerebral parenchyma, and 18 normal subjects were studied. The results show that amplitude asymmetries over 4 microV (between responses evoked by right and left hemifield stimulation, recorded ipsilaterally to the stimulated hemifield) are clinically relevant for hemianopic visual field defect. Significant correlations were found between the VEP features and the site of the damage: lesions of the occipital cortex were generally found to cause more pronounced bioelectrical abnormalities than those due to lesions affecting the visual pathways, with cortical sparing.

Adolescent↗
PubMed1999

Cytidine-5'-diphosphocholine (citicoline) improves retinal and cortical responses in patients with glaucoma.

PURPOSE: To evaluate the effects of cytidine-5'-diphosphocholine (citicoline) on retinal function and on cortical responses in patients with glaucoma. DESIGN: Randomized clinical trial. PARTICIPANTS: Forty patients with open-angle glaucoma were randomly divided into two age-matched groups: citicoline group ([GC] n = 25) and placebo group ([GP] n = 15). METHODS: The GC patients were treated with Neuroton (citicoline, 1000 mg/day intramuscularly) for 60 days; GP patients were treated with placebo (physiologic solution with additives) for 60 days. After 120 days of washout (day 180), the GC patients were divided into two age-matched groups: in 10 patients (GC1 group) the washout was prolonged for a further 120 days; in 15 patients (GC2 group) a second 60-day period of citicoline treatment was followed by a second 120-day period of washout. At day 180, the washout was extended for another 180 days in GP patients. In all subjects, retinal and cortical responses were evaluated by simultaneous recordings of visual evoked potentials (VEPs) and pattern-electroretinograms (PERGs) at baseline, after 60 days, and after 180 days. At day 300, VEPs and PERGs were also evaluated in GC1 patients, and at 240 and 360 days in GC2 and GP patients. MAIN OUTCOME MEASURES: Visual evoked potential parameters (P100 latency and N75-P100 amplitude); PERG parameters (P50 latency and P50-N95 amplitude); and intraocular pressure. RESULTS: The GP patients displayed similar VEP and PERG parameters in all examinations performed. In GC patients, the treatment with citicoline induced a significant (P < 0.01) improvement of VEP and PERG parameters, and their values were significantly different (P < 0.01) with respect to those of GP patients (P < 0.01). Visual evoked potentials and PERGs, recorded in GC patients after washout, revealed that although there was a worsening trend, the electrophysiologic improvement was still maintained. After a second period of washout, GC1 patients had VEP and PERG parameters similar (P > 0.05) to baseline ones and to those of GP patients. In GC2 patients, a second period of citicoline treatment induced a further (P < 0.01) improvement of VEP and PERG parameters CONCLUSION: Citicoline may induce an improvement of the retinal and of the visual pathway function in patients with glaucoma.

Cytidine Diphosphate Choline↗
PubMed2001

Raised visual detection thresholds depend on the level of complexity of cognitive foveal loading.

The objective of the study was to measure the interactions between visual thresholds for a simple light (the secondary task) presented peripherally and a simultaneously performed cognitive task (the primary task) presented foveally The primary task was highly visible but varied according to its cognitive complexity. Interactions between the tasks were determined by measuring detection thresholds for the peripheral task and accuracy of performance of the foveal task. Effects were measured for 5, 10, 20, and 30 deg eccentricity of the peripherally presented light and for three levels of cognitive complexity. Mesopic conditions (0.5 lx) were used. As expected, the concurrent presentation of the foveal cognitive task reduced peripheral sensitivity. Moreover, performance of the foveal task was adversely affected when conducting the peripheral task. Performance on both tasks was reduced as the level of complexity of the cognitive task increased. There were qualitative differences in task interactions between the central 10 deg and at greater eccentricities. Within 10 deg there was a disproportionate effect of eccentricity, previously interpreted as the 'tunnel-vision' model of visual field narrowing. Interactions outside 10 deg were less affected by eccentricity. These results are discussed in terms of the known neurophysiological characteristics of the primary visual pathway.

Adult↗