Visual Pathway

Background: Tupaia belangeri is increasingly recognized as an essential animal model in neuroscience, metabolic disorders and emerging infectious diseases due to its close phylogenetic relationship to primates and its small body size. Phenotypic traits are crucial for studying biological systems. Tree shrews are widely used in environmental adaptation research due to their genetic diversity and phenotypic polymorphism. The measurement of its physical indicators and skull provides a new perspective for exploring the adaptive characteristics of different tree shrew populations. Establishing population-specific morphometric reference values is therefore essential for standardizing veterinary dosing and ensuring translational reliability when tree shrews are used as models for metabolic, neurodegenerative, or emerging infectious diseases. Methods: To elucidate the phenotypic diversity of the Tree shrew (Tupaia belangeri) and its relationship with environmental factors, the present study measured the body shape and skull indicators of 134 individuals across 12 regions. Result: The results showed that there had significant phenotypic differences between different geographic populations, with inter population variation significantly greater than intra population variation, indicating that differentiation mainly occurs between populations. Especially Daxin population (T. b. tonquinia) and the Hainan population (T. b. modesta) had larger body mass and length, whereas the Kunming population (T. b. chinensis) was relatively smaller. Environmental factor analysis revealed significant correlations between latitude, altitude, annual average temperature, atmospheric pressure and precipitation with the morphological traits of tree shrews, with altitude had the most significant impact on phenotypic differences. The clustering and principal component analysis results also confirmed the geographical differentiation of the tree shrew in morphological studies. The research findings emphasized the role of environmental factors in shaping the phenotypic diversity of the tree shrew and provide important insights into the evolution and ecological adaptation of this species, which was of great significance for biodiversity conservation and ecosystem management.

The objective of this research was to find the likely importance of variations in aerobic fitness between men volleyball players competing for club and university. The volleyball players must have the capacity to comprehensively display their physical, technical, tactical, and psychological skills. The physical attributes of players have a noticeable impact on both the team's strategy and the players' performance. Players must therefore be physically capable of meeting the demands of the sport. The present study was planned to monitor the cardio-respiratory fitness or aerobic endurance of male volleyball players at the club and university levels and to compare the results. A total number of 60 men volleyball players, aged 19 to 24 years from both clubs and universities participated in this study. To assess each group's level of aerobic fitness, the test that was used is the Harvard step test. Findings demonstrated a difference in club and university players' aerobic fitness of a significant level (p< 0.05). In comparison to club volleyball players, university volleyball players were shown to have superior aerobic fitness.

Electroretinogram (ERG) and visual‐evoked potentials (VEPs) are used in veterinary ophthalmology to assess the functional integrity of the retina and the central visual pathway. The interpretation of altered electrophysiologic potentials in diseases can be of great diagnostic value, although it is important to be aware of technical factors and the limitations of these techniques which may result in over‐interpretation and misinterpretation of the recordings, such that they are similar to those found in disease‐related electrophysiologic changes. The recorded potentials represent the differences in voltage between the active and reference electrodes. The ground electrode serves as zero. A differential or instrumentation amplifier selectively amplifies signals of interest while rejecting noise. Differences between inputs are amplified, whereas common signals are rejected in a process called common mode rejection (CMR). In order for CMR to be most effective in reducing noise, the elect...

We present Fireflies, a bio-inspired visualization using animal swarming behaviour and plant phyllotaxis. We applied Fireflies to a Canadian attitudinal survey on HIV/AIDS, using motion to depict participants' comfort levels concerning HIV+ people. The bio-inspired visual properties of Fireflies meld into an expressive and engaging representation of sensitive data.

We investigated whether the topographically organized, category-related patterns of neural response in the ventral visual pathway are a representation of sensory images or a more abstract representation of object form that is not dependent on sensory modality. We used functional MRI to measure patterns of response evoked during visual and tactile recognition of faces and manmade objects in sighted subjects and during tactile recognition in blind subjects. Results showed that visual and tactile recognition evoked category-related patterns of response in a ventral extrastriate visual area in the inferior temporal gyrus that were correlated across modality for manmade objects. Blind subjects also demonstrated category-related patterns of response in this “visual” area, and in more ventral cortical regions in the fusiform gyrus, indicating that these patterns are not due to visual imagery and, furthermore, that visual experience is not necessary for category-related representations to d...

Background: Asymtomatic santral nervous system disorder is frequently found in patients with diabetes. Neurophysiological tests were found to be objective and sensitive tool for detecting subclinical optic nerve and CNS disorders. Objectives: Our aim is to evaluate of the central nerve conduction changes using visual evoked potentials (VEP) and to demonstrate the effects of various risk factors on VEP parameters in children with type 1 diabetes mellitus (T1DM). Methods: Sixty children aged between 6 and 18 years and followed-up with a diagnosis of T1DM were enrolled in the study. Thirty healthy, age-matched children were enrolled as the control group. All patients and controls underwent the pattern reversal visual evoked potentials (PRVEP) test. Patients' HbA1c values, age, sex and duration of disease were evaluated from their hospital files. Results: Both right and left VEP latencies were significantly longer in the diabetic group than in the control group (P = 0.001 and P = 0.001, respectively). The mean duration of T1DM in the patient group was 5.5 years (min: 1 -max: 15). There was a positive correlation between longer VEP latency values and duration of DM, with coefficients of 0.49 for the right eye and 0.513 for the left eye (P < 0.001 and P < 0.001, respectively). Conclusions: We found that optic nerve conduction diminished significantly in children with T1DM. Visual evoked potential datas showed a significant prolongation of the latency of P-100. We recommend that all diabetic children be scanned with neurophysiological tests such as PRVEP for optic neuropathy.

We extend a neural network model, developed to examine neural correlates for the dynamic synthesis of edges from luminance gradients , to account for the effects of exposure duration, base blur and contrast on the perceived sharpness of edges. This model of REtino-COrtical Dynamics (RECOD) predicts that (i) a decrease in exposure duration causes an increase in the perceived blur and the blur discrimination threshold for edges, (ii) this increase in perceived blur is more pronounced for sharper edges than for blurred edges, (iii) perceived blur is independent of contrast while the blur discrimination threshold decreases with contrast, (iv) perceived blur increases with increasing base blur while the blur discrimination threshold has a nonmonotoni c U-shaped dependence on base blur, (v) the perceived location of an edge shifts progressively towards the lowluminance side of the edge with increasing contrast, and (vi) perceived contrast of suprathreshold stimuli is essentially independent of spatial frequency over a wide range of contrast values. These predictions are shown to be in quantitative agreement with existing psychophysical data from the literature and with data collected on three observers to quantify the effect of exposure duration on perceived blur.

Two line gratings abutting each other with a phase shift of half a cycle elicit the perception of an illusory line running orthogonany between the two sets of grating lines. We found that rating strength increases with increasing number of lines, line length, and phase angle. In contrast, rating strength decreases with increasing spacing of lines, lateral misalignment, rotation of one grating relative to the other, and line width. There is a pronounced oblique effect at 45 deg when the orientation of the abutting gratings is changed from horizontal through diagonal to vertical. Findings are interpreted in terms of a neurophysiological model. We conclude that the end-stopped receptive fields activated by the grating lines are about 6 deg long and 2 deg wide. On the other hand, the "response fields" of the cells, integrating orthogonally across line ends, are assumed to be 5 deg long and less than 1 deg wide. The psyehophysical data compare favorably with available neurophysiological data in Area V2 of the macaque suggesting that the perception of illusory contours in human observers may be based on cortical cell properties similar to those found in the monkey.

Along the processing chain in the visual pathway the pattern electroretinogram (PERG) is a better indicator of the peripheral function than the visual evoked potential (VEP). Therefore the PERG and the VEP will be impaired equally by disturbances before the ganglion cell layer (e.g., blurred image or retinal disease) and differently by further centrally located diseases (e.g., tumor compression of the optic nerve). Thus in patients complaining of reduced visual acuity who show disturbed VEP but a normal PERG, malingering can be definitely ruled out. Representative combinations of PERG and VEP findings are described.

We present a generalized theoretical framework for olfactory representation and plasticity, using the theory of smooth manifolds and sheaves to depict categorical odor learning via distributed neural computation. Beginning with the space of all possible inputs to the olfactory system, we develop a dynamic model for odor learning that culminates in a perceptual space in which categorical odor representations are hierarchically constructed through experience, exhibiting statistically appropriate consequential regions and clear relationships between the broader and narrower identities to which a given odor might be assigned. The model reflects both the sampling-based physical similarity relationships among odorants, as observed in physiological receptor response profiles, and the acquired, learning-dependent perceptual similarity relationships among odors that can be measured behaviorally, and defines the relationship between them. Individual training and experience generates correspondingly more sophisticated odor identification capabilities. Because these odor representations are constructed from experience and depend on local, distributed plasticity mechanisms, geometries that fix curvature are insufficient to describe the capabilities of the system. This generative framework also encompasses hypotheses explaining representational drift in postbulbar circuits and the context-dependent remapping of perceptual similarity relationships.

Cobaltous-lysine is transported anterogradely from the optic nerve of the teleost, Lethrinus chrysostomus (Lethrinidae, Perciformes). The marginal optic tract is labelled in longtitudinal bands of light and dark staining fibres which persists caudally within the ventral division but not in the dorsal division. This species possesses multiple central targets in the contralateral preoptic, diencephalic, pretectal, periventricular and tectal regions of the brain. In addition, a greater subdivision of the marginal optic tract is found to project to various nuclei. Ipsilateral projections are found in the suprachiasmatic nucleus and in the region of the horizontal commissure. Projections are also found in the telencephalic region of the nucleus olfactoretinalis and the thalamic region of the nucleus thalamoretinalis. The retinotopicity of some of these nuclei, found in previous studies, is discussed in relation to the possibility of specific sub-populations of retinal ganglion cells having different central targets.

Cobaltous-lysine is transported anterogradely from the optic nerve of the teleost, Lethrinus chrysostomus (Lethrinidae, Perciformes). The marginal optic tract is labelled in longtitudinal bands of light and dark staining fibres which persists caudally within the ventral division but not in the dorsal division. This species possesses multiple central targets in the contralateral preoptic, diencephalic, pretectal, periventricular and tectal regions of the brain. In addition, a greater subdivision of the marginal optic tract is found to project to various nuclei. Ipsilateral projections are found in the suprachiasmatic nucleus and in the region of the horizontal commissure. Projections are also found in the telencephalic region of the nucleus olfactoretinalis and the thalamic region of the nucleus thalamoretinalis. The retinotopicity of some of these nuclei, found in previous studies, is discussed in relation to the possibility of specific sub-populations of retinal ganglion cells having different central targets.

Reaching implies effector and target locations to be computed and updated continuously all along the visuo-motor transformation process, before and during movement execution, aiming in making these instantaneous locations coincide spatially. So instead of a neuro-anatomical dissociation between areas devoted to motor planning versus control, there might be 1) an automatic pathway of visual-to-motor transformation which relies on a comparison at the level of oculo-centric coordinates between visual target and hand locations from multimodal sources of information and 2) intentional pathways relying on the allocentric comparison between visual locations of the hand and of the target. Converging evidence from patients with optic ataxia, neuroimaging and transcranial magnetic stimulation techniques, and investigations in primates, has led to ascribe the automatic pathway to the direct connection between the medio-dorsal occipito-parietal cortex (the caudal part of the superior parietal lobule) and the dorsal premotor cortex (and further the primary motor cortex). Studies involving patients with visual agnosia (inferotemporal cortex), Parkinson disease (basal ganglia) or neglect (inferior parietal lobule) have put forward a more diffuse putative neural substrate for the intentional visual-to-motor pathway. If most strokes affect the intentional motor function while preserving the automatic pathway of visual-to-motor transformation, we propose a new rehabilitation method for hemiparesia relying on the stimulation of the automatic pathway using moving rather than stationary objects. Preliminary data are included.

The visibility of stationary phantoms was measured by human observers in two experiments. The phantom visibility declined with the increase of the mean luminance of black[white inducing gratings, falling near to zero at a mean luminance high above 80 ed/m 2. The phantoms also disappeared when the red/green inducing gratings were subjectively equiluminant. The implications of these results are discussed in relation to the grating induction effect and to the functional correlations with the magnoceHular system's activity.

Ocular manifestations of antiphospholipid syndrome typically include thromboembolic and neuro-ophthalmic complications. In this report we present a case of inflammation of the ocular coats in a patient diagnosed with antiphospholipid syndrome 16 years prior. We discuss management of the case and the possible aetiology of the rare association.

Objectives: To assess if anti-C1q and other markers of disease activity are associated with nephritis according to renal BILAG score in a population of patients with SLE. Methods: A sample of portuguese SLE patients was grouped according to BILAG renal score: categories A+ B+ C (active nephritis), category D (inactive nephritis) and category E (no nephritis). Anti-C1q autoantibodies were determined by ELISA (Bühlmann®) with duplicate samples. Levels < 15 units/ mL were considered the cut-off for normal sera. Serum ESR, CRP, levels of C3c, C4, CH50, anti-DNAds titres, 25(OH)vitamin D, 24 hour protein excretion and SLEDAI were measured. A multivariate analysis was performed using SPSS 18.0. Adjustments were made for patients´age, disease duration, steroid daily dose (prednisolone equivalents) and hydroxychloroquine daily dose. Results: 160 patients, 148 (92.5%) women, with mean (SD) age of 44.2± 12.59 years, were grouped according to BILAG renal score in categories A+B+C (n=23; 14.4%), category D (n=45; 28.1%) and category E (n=92; 57.5%). All the patients with a history of nephritis (active or previous) had had a biopsy at the time of its diagnosis (n=68; 42.5%). They had mean (SD) disease duration of 12.2± 8.71 years, SLEDAI 3.1± 4.50, SLICC 0.6± 1.07, daily dose of prednisolone 6.5 ± 5.91 mg and of hydroxychloroquine 213.2± 192.76 mg. An association was found between active renal disease (BILAG score categories A+ B+ C) and higher anti-C1q titres (p<0.01), higher anti-dsDNA titres (p<0.01) and lower C3c levels (p<0.01). Conclusions: In a cohort of portuguese SLE patients, an association was found between anti-C1q titres, C3c levels and anti-dsDNA titres with active nephritis evaluated by BILAG renal scores. These data support the use of anti-C1q as a marker of nephritis presence and activity in SLE. References: Yang XW, Tan Y, Yu F, Zhao MH, Combination of anti-C1q and anti-dsDNA antibodies is associated with higher renal disease activity and predicts renal prognosis of patients with lupus nephritis.

Central vision is substantially over represented in the lateral geniculate nucleus (dLGN) and striate cortex. The over representation could be accompanied by a selective expansion of central vision in parvocellular dLGN, in which case the ratio of parvocellular to magnocellular inputs to striate cortex should change with retinal eccentricity. To test this, sample ratios were determined from counts of neurons in dLGN labelled retrogradely with WGA-HRP from striate cortex at the cortical representations of various eccentricities. Parvocellular to magnocellular ratios decreased from a mean of 35:1 at the fovea to 5:1 at 15°eccentricity. Furthermore, they exceeded the ratio of Pb to Pa ganglion cells in central retina, but not in peripheral retina, showing that the uneven P to M ratio in the LGN does not merely mirror the distribution of ganglion cells in the retina. This provides direct evidence for selective over representation of central vision in parvocellular dLGN.

Four patients with functional hemispherectomy, one patient with a complete anatomical hemispherectomy, and one patient with unilateral removal of the temporal, parietal and occipital lobes took part in two sets of experiments designed to investigate their residual sensitivity to motion-in-depth in the hemianopic visual field. Two types of computer-generated visual displays were used; in the first set of experiments, a dot pattern and in the second, a circular checkerboard. These simulated either convergent, divergent or reversed rotational motion. Each set of experiments consisted of two parts; in the first part, electrodermal responses were monitored during stimulus presentation while the subjects performed a simple distracting task. In the second part, subjects were asked to state verbally the direction of stimulus motion. Contrary to expectations, no reliable changes in skin conductance were elicited from any of the subjects by changes in the direction of motion of the component parts of either the dot pattern display or the circular checkerboard display. Furthermore, none of the subjects were able to discriminate the direction of motion of the target patterns when presented in the hemianopic field. The most parsimonious explanation is that the subcortical visual pathways which survive hemispherectomy are unable to process visual information relating to motion in depth.

Visual search for target items embedded within a set of distracting items has consistently been shown to engage regions of occipital and parietal cortex, but the contribution of diVerent regions of prefrontal cortex remains unclear. Here, we used fMRI to compare brain activity in 12 healthy participants performing eYcient and ineYcient search tasks in which target discriminability and the number of distractor items were manipulated. Matched baseline conditions were incorporated to control for visual and motor components of the tasks, allowing cortical activity associated with each type of search to be isolated. Region of interest analysis was applied to critical regions of prefrontal cortex to determine whether their involvement was common to both eYcient and ineYcient search, or unique to ineYcient search alone. We found regions of the inferior and middle frontal cortex were only active during ineYcient search, whereas an area in the supe-rior frontal cortex (in the region of FEF) was active for both eYcient and ineYcient search. Thus, regions of ventral as well as dorsal prefrontal cortex are recruited during ineYcient search, and we propose that this activity is related to processes that guide, control and monitor the allocation of selective attention.

Thyroid hormone deficiency in the developing brain leads to disorders of neuronal process growth. This is evidenced by reduced axonal and dendritic size and complexity (Garza et al.: Developmental Brain Research 43:287‐297, 1988; Ruiz‐Marcos: Iodine and the Brain. New York; Plenum Press, pp 91‐102, 1989). These findings may be related to alterations in the neuronal cytoskeleton in hypothyroidism, such as reduced or abnormal microtubular number and density (Faivre et al.: Developmental Brain Research 8:21‐30, 1983), and altered assembly, stabilization, and composition of microtubule protein in the hypothyroid brain. Neurofilaments also contribute to axonal caliber and process stability. Similar to microtubules, certain properties of neurofilaments are altered in developing hypothyroid axons (Marc and Rabie: In‐ternational Journal of Developmental Neuroscience 3:353‐358, 1985; Faivre et al.: Developmental Brain Research 8:21‐30, 1983) that may affect axonal caliber and process stabili...

The goal of this study was to explore the functional organization of direction of motion in cat area 18. Optical imaging was used to record the activity of populations of neurons. We found a patchy distribution of cortical regions exhibiting preference for one direction over the opposite direction of motion. The degree of clustering according to preference of direction was two to four times smaller than that observed for orientation. In general, direction preference changed smoothly along the cortical surface; however, discontinuities in the direction maps were observed. These discontinuities formed lines that separated pairs of patches with preference for opposite directions. The functional maps for direction and for orientation preference were closely related; typically, an iso-orientation patch was divided into regions that exhibited preference for opposite directions, orthogonal to the orientation. In addition, the lines of disconti-nuity within the direction map often connected points of singularity in the orientation map. Although the organization of both domains was related, the direction and the orientation selective responses were separable; whereas the selective response according to direction of motion was nearly independent of the length of bars used for visual stimulation, the selective response to orientation decreased significantly with decreasing length of the bars. Extensive single and multiunit electrical recordings, targeted to selected domains of the functional maps, confirmed the features revealed by optical imaging. We conclude that significant processing of direction of motion is performed early in the cat visual pathway.

Prenatal unilateral enucleation in mammals causes an extensive anatomical reorganization of visual pathways. The remaining eye innervates the entire extent of visual subcortical and cortical areas. Electrophysiological recordings have shown that the retino-geniculate connections are retinotopically organized and geniculate neurones have normal receptive field properties. In area 17 all neurons respond to stimulation of the remaining eye and retinotopy, orientation columns, and direction selectivity are maintained. The only detectable change is a reduction in receptive field size. Are these changes reflected in the visual behavior? We studied visual performance in cats unilaterally enucleated 3 weeks before birth (gestational age at enucleation, 39-42 days). We tested behaviorally the development of visual acuity and, in the adult, the extension of the visual field and the contrast sensitivity. We found no difference between prenatal monocularly enucleated cats and controls in their ...

Crist, Roy E., Mitesh K. Kapadia, Gerald Westheimer, and Charles D. Gilbert. Perceptual learning of spatial localization: specificity for orientation, position, and context. J. Neurophysiol. 78: 2889–2894, 1997. Discrimination of simple visual attributes can improve significantly with practice. We have trained human observers to perform peripherally presented tasks involving the localization of short line segments and examined the specificity of the learning for the visual location, orientation, and geometric arrangement of the trained stimulus. Several weeks of training resulted in dramatic threshold reductions. The learning was specific for the orientation and location of the trained stimulus, indicating the involvement of the earliest cortical stages in the visual pathway where the orientation and location of stimuli are mapped with highest resolution. Furthermore, improvement was also specific for both the configuration of the trained stimulus and the attribute of the stimulus t...

of parafoveal macaque ganglion cells were measured as a function of the contrast and position of an edge flashed within their receptive fields. The goal was to determine the ability of different cell types to signal edge location. For comparison, parafoveal vernier thresholds of human observers were measured with pairs of flashed edges. Cells of the magnocellular (MC-) pathway gave larger responses than cells of the parvocellular (PC-) pathway. Neurometric analyses comparing a cell's response at different edge positions were performed. The positional signal from single MC-pathway cells was more precise than from PC-pathway cells, especially at lower contrasts. In a second analysis, based on the neurophysiological results, responses from a matrix of ganglion cells were generated. Using a simple model, vernier performance expected from such a matrix was predicted as a function of edge length and contrast. Again, file MC-pathway gave a more precise positional signal than the PC-pathway despite the latter's numerical advantage. At contrasts of 20% and below, only the MC-pathway would appear capable of supporting vernier performance with our stimuli. At higher contrasts either the MC-or PC-pathway could provide an adequate signal.

Aims/hypothesis To study long-term changes in retinal function in response to sustained glycaemia reduction in participants with type 1 diabetes. Methods Prospective study using objective measures of retinal function in 17 participants with type 1 diabetes mellitus and minimal to moderate retinopathy who switched from conventional subcutaneous injection to continuous subcutaneous infusion of insulin (CSII). Results Glycated haemoglobin HbA 1c gradually decreased from 9.1% at baseline before CSII to 7.4% after 1 year on CSII. Glycaemia was markedly reduced within 1 week after initiation of CSII and remained stable thereafter. Dark adaptation and retinal electroretinographic function at 1, 4 and 16 weeks after initiation of CSII were comparable with baseline values, whereas a significant improvement in rod photoreceptor dark adaptation and dark-adapted b-wave amplitudes were seen after 52 weeks (time to rod-cone break -25% [p< 0.0001], time to a standardised rod intercept -13% [p<0.0001], dark-adapted rod b-wave fullfield amplitude +15% [p=0.0125], standard combined rodcone b-wave amplitude +8% [p=0.049]). No detectable change was observed in cone adaptation, electroretinographic cone function or retinopathy. Conclusions/interpretation After initiation of CSII, the retinal visual pathway of the rods improved with a delay of more than 4 months, over a time scale comparable with the duration of the diabetic retinopathy early worsening response to sustained glycaemia reduction. This indicates that glycaemia has a long-term effect on the disposition of functional capacity in the retinal visual pathway of rod photoreceptors, the cells that appear to be driving the development of diabetic retinopathy.

Aims/hypothesis To study long-term changes in retinal function in response to sustained glycaemia reduction in participants with type 1 diabetes. Methods Prospective study using objective measures of retinal function in 17 participants with type 1 diabetes mellitus and minimal to moderate retinopathy who switched from conventional subcutaneous injection to continuous subcutaneous infusion of insulin (CSII). Results Glycated haemoglobin HbA 1c gradually decreased from 9.1% at baseline before CSII to 7.4% after 1 year on CSII. Glycaemia was markedly reduced within 1 week after initiation of CSII and remained stable thereafter. Dark adaptation and retinal electroretinographic function at 1, 4 and 16 weeks after initiation of CSII were comparable with baseline values, whereas a significant improvement in rod photoreceptor dark adaptation and dark-adapted b-wave amplitudes were seen after 52 weeks (time to rod-cone break -25% [p< 0.0001], time to a standardised rod intercept -13% [p<0.0001], dark-adapted rod b-wave fullfield amplitude +15% [p=0.0125], standard combined rodcone b-wave amplitude +8% [p=0.049]). No detectable change was observed in cone adaptation, electroretinographic cone function or retinopathy. Conclusions/interpretation After initiation of CSII, the retinal visual pathway of the rods improved with a delay of more than 4 months, over a time scale comparable with the duration of the diabetic retinopathy early worsening response to sustained glycaemia reduction. This indicates that glycaemia has a long-term effect on the disposition of functional capacity in the retinal visual pathway of rod photoreceptors, the cells that appear to be driving the development of diabetic retinopathy.

Previous studies have shown a noticeable phenotypic diversity for pyramidal cells among cortical areas in the cerebral cortex. Both the extent and systematic nature of this variation suggests a correlation with particular aspects of cortical processing. Nevertheless, regional variations in the morphology of inhibitory cells have not been evaluated with the same detail. In the present study we performed a 3D morphometric analysis of 120 NADPH diaphorase (NADPH-d) type I neurons in the visual cortex of a South American Hystricomorph rodent, the diurnal agouti (Dasyprocta sp.). We found significant differences in morphology of NADPH-d type I neurons among visual cortical areas: cells became progressively larger and more branched from V1 to V2 and V3. Presumably, the specialized morphology of these cells is correlated with different sampling geometry and function. The data suggest that area-specific specializations of cortical inhibitory circuitry are also present in rodents.

The visual pathway that leads from the retina to the tangential cells in the third optical ganglion of the fly is a sophisticated system for the detection of visual motion. The tangential cells, whose responses are thought to characterize the state of egomotion of the animal, show a remarkable ability to encode velocity information about optic flow patterns to which they are sensitive, independent of the structure and contrast of viewed scenery. We describe a simulation study based on a model that accounts for key physiological features observed in the biological system, which contains nonlinear features that we expect to contribute to this capability. One of these features is motion adaptation, a phenomenon on which recent research has shed new light. We conclude that our models significantly reduce dependence of response on variable natural scenery, although they still do not perform as well in this respect as the biological neurons. This biological system has inspired an implementation of visual motion processing in analog VLSI technology. The neuromorphic circuits are intended for eventual on-or near-focal plane integration with photosensing. We describe the design approach and present results from preliminary versions of these circuits.

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 t angential 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.

It has been suggested that albinolike misrouting of the visual pathway occurs in patients with dissociated vertical deviation (DVD). We re-examined this contention in ten D V D patients using visually evoked potentials. Full-field monocular pattern-onset checkerboard stimulation was employed. The visually evoked potentials were recorded simultaneously from both occipital lobes. Their differential activity during stimulation of the right eye was compared with that obtained during stimulation of the left. We found no predominance of crossed projection in any of the D V D cases. The results in nine normal subjects were similar. In 13 albino patients, however, there was a relative positivity in the contralateral hemisphere about 100 ms after pattern-onset, which reconfirmed predominance of the crossed projection. Possible artifacts are discussed that may have led to the assumption of misrouting in D V D in two previous reports.

Visual evoked potentials (VEPs) can provide important diagnostic information regarding the functional integrity of the visual system. This document updates the ISCEV standard for clinical VEP testing and supersedes the 2004 standard. The major change in this revision is that test parameters have been made more precise to achieve better consistency of results within and between test centers. The ISCEV standard VEP protocols are defined for a single recording channel with a midline occipital active electrode. These protocols are intended for assessment of prechiasmal function; additional electrode sites are recommended for evaluation of chiasmal and postchiasmal function. ISCEV has selected a subset of stimulus and recording conditions that provide core clinical information and can be performed by most clinical electrophysiology laboratories throughout the world. These are: 1. Pattern-reversal VEPs elicited by checkerboard stimuli with large 1°(i.e., 60 min of arc; min) and small 0.25°(15 min) checks. 2. Pattern onset/ offset VEPs elicited by checkerboard stimuli with large 1°(60 min) and small 0.25°(15 min) checks. 3. Flash VEP elicited by a brief luminance increment, a flash, which subtends a visual field of at least 20°.

found a nasal-temporal asymmetry of visually evoked potentials (VEP) elicited by motion stimuli in patients with infantile strabismus. Patients with infantile strabismus typically present with an asymmetry of the monocular optokinetic nystagmus (OKN). We here address the question whether the asymmetry of the motion VEP indicates a sensory defect in the afferent visual pathway that could explain the OKN asymmetry. We recorded the VEP to a horizontally oscillating vertical sinusoidal grating in 20 patients with infantile strabismus (esotropia, asymmetry of the monocular optokinetic nystagmus, latent ',tagmus) and in 10 normal controls. No asymmetry occurred in the 10 controls. Eight of the 20 patients with infantile strabismus showed a clear difference between the VEPs evoked by back and forth movements with a mirror-like asymmetry between the two eyes (phase shift 1804-20°). However, there was no significant correlation between the degree of VEP and OKN asymmetries. Therefore, we assume that the VEP asymmetry does not reflect the primary cause of the OKN asymmetry. Rather, the OKN asymmetry may be due to a sensory-motor defect in the efferent subcortical pathway, and the VEP asymmetry could be an epiphenomenon. Some of the VEP asymmetry may be a consequence of the latent nystagmus typically released under monocular stimulation, leading to adaptation of the afferent retino-cortical pathway. This suggestion is supported by a marked VEP asymmetry that we found in two patients with an acquired central vestibular nystagmus, an abnormality most likely not combined with a primary defect of the retino-cortical pathway.

Visual electrophysiology allows non-invasive monitoring of the function of most processing stages along the visual pathway. Here, we consider which of the available methods provides the most information concerning glaucomatous optic nerve disease. The multifocal electroretinogram (ERG), although often employed, is less affected in glaucoma than two direct measurements of retinal ganglion cell function, namely the pattern ERG (PERG) and the photopic negative response (PhNR) of the ERG. For the PERG, longitudinal studies have been reported, suggesting that this method can be used for the early detection of glaucoma; for the PhNR, no longitudinal study is available as yet. The multifocal PERG can spatially resolve ganglion cell function but its glaucomatous reduction is typically panretinal, even with only local field changes and so, its topographic resolution is of no advantage in glaucoma. The multifocal visual evoked potential promises objective perimetry and shows sensitivity and specificity comparable with standard automated perimetry but has not been established as a routine tool to date.

The visual system of the macaque monkey has provided a useful model for understanding the neural basis of human vision, yet, there are few detailed comparisons of neural populations other than photoreceptors for the two species. Using intracellular staining in an in vitro preparation of the isolated and intact human retina, we have characterized the relationship of dendritic field size to retinal eccentricity for the two major ganglion cell classes, the midget and the parasol cells. We report three findings. (i) The difference in dendritic field diameter between the parasol and midget cells increases from a ratio of approximately 3:1 in the retinal periphery to approximately 10:1 at 3 degrees eccentricity, suggesting that human midget cells may outnumber parasol cells by as much as 30:1 in the central retina. (ii) The dendritic fields of human ON-center parasol and midget cells are 30-50% larger in diameter than their OFF-center counterparts, suggesting a distinct asymmetry in the h...

We injected botulinum toxin into the horizontal rectus muscles of the right eyes of 2 patients who had acquired pendular nystagmus with horizontal, vertical, and torsional components. This treatment successfully abolished the horizontal component of the nystagmus in the injected eye in both patients for approximately 2 months. Both patients showed a small but measurable improvement of vision in the injected eye that may have been limited by coexistent disease of the visual pathways. The vertical and torsional components of the nystagmus persisted in both patients. In 1 patient, the horizontal component of nystagmus in the noninjected eye increased; we ascribe this finding to plastic adaptive changes in response to paresis caused by the botulinum toxin. Such plastic-adaptive changes and direct side effects of the injections-such as diplopia and ptosis-may limit the effectiveness of botulinum toxin in the treatment of acquired nystagmus. Neither patient elected to repeat the botulinum treatment.

Whether position and orientation shifts induced by monocular context also act as a disparity for purposes of stereoscopy was investigated experimentally in order to examine the extent to which lateral spatial localization and stereoscopic depth share circuitry. A monocular tilt illusion in a line does not lead to a commensurate depth tilt of that line in binocular view, nor does a position shift in a bisection task caused by a gap within monocular dynamic random noise produce the commensurate depth displacement. Interocular transfer of monocularly-induced shifts, which might explain such findings, was eliminated as a factor. The results can therefore be interpreted as indicators of channeling and ordering of spatial signals paths in the visual cortex and imply that two-dimensional contextual interactions operate at a processing level beyond where disparity has already been extracted.

This report presents a patient with Devic's neuromyelitis optica associated with primary Sjögren's syndrome. Her first attack was right-sided optic neuritis at age 10 years. Attacks involving both optic nerves and medulla spinalis were recorded during the ensuing years. The diagnosis of Sjögren's syndrome could not be made until the second decade because it was not suspected.

Objective: Retinal nerve fiber layer (RNFL) abnormalities detected by optical coherence tomography (OCT) are useful markers for axonal loss and visual dysfunction in multiple sclerosis (MS), but their role in routine clinical management is not well-studied. Methods: Clinical and OCT examinations were performed on 240 patients attending a neurology clinic. Using OCT 5th percentile to define abnormal RNFL thickness, we compared eyes classified by neurologists as having optic atrophy to RNFL thickness, and afferent pupillary defect (APD) to RNFL thickness ratios of eye pairs.

By using immunohistochemical methods, we examined the distribution of cells expressing subunits of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA)‐selective glutamate receptors (GluR2/3) in the cortical areas of the occipitotemporal pathway in monkeys. GluR2/3‐immunoreactive (‐ir) cells were primarily pyramidal cells; this category, however, also included large stellate cells in layer IVB of the striate cortex (V1) and fusiform cells in layer VI of all the areas examined. GluR2/3 immunoreactivity differed among the areas in laminar distribution and intensity. In V1, GluR2/3‐ir cells were identified mainly in layers II, III, IVB, and VI. The prestriate areas V2 and V4 and the inferior temporal areas TEO and TE contained GluR2/3‐ir cells in layers II, III, and VI. In the TE, GluR2/3‐ir cells were also abundant in layer V. In area 36 of the perirhinal cortex, neurons in layers II, III, V, and VI were labeled in a similar manner to the TE labeling, but with greater staining inte...

1. The effects produced by repetitive i-v. administration of naloxone (I, 2 or 4 mg/kgf on the visual evoked potentials (VEPsl recorded along the main and accessory visual pathways were investigated in a modified "encephale isole" cat preparation. 2. Naloxone provoked a progressive amplitude enhancement and latency reduction of some components, depending on the structure analyzed, the dose used and the number of administrations applied. Electroretinogram (ERG) and Nl-Pl VEP components of optic chiasm (OCh), lateral geniculate body (LGB) and visual cortex (VC) did not present significant changes. 3. Late-latency components (more than 200 msec) appeared in the VEPs of LGB and VC, mainly when 4 mg/kg were used. 4. Our results suggest that endogenous opioids have a modulatory role in the processing of sensory information at different levels of the visual system.

Attention is important for sufficient performance on many visual tasks. This has been shown using achromatic steady‐state and pattern‐reversal VEPs. Waveform characteristics typically attenuate when attending to distractor stimuli and ignoring VEP stimuli. Chromatic pattern‐onset responses have not been tested under conditions of selective attention: as they can be used in clinical settings to test color vision, it is important to know what effects attentional shifts would have on this response. In the present study chromatic pattern‐onset VEPs were recorded using spatially divided and spatially contiguous VEP and distractor stimuli. VEP stimuli were 1 cycle.deg−1 horizontal sine wave patterns (onset mode 100 ms on/400 ms off) used to selectively modulate the L−M and S‐(L+M) visual pathways. Distracter stimuli were letters. Subjects attended to either the letters or the gratings and pressed a button when a predetermined stimulus appeared. In Experiment one, VEP and distractor stimul...

Intra-ocular pressure (IOP) increases to double that of its normal level under full-body inversion, in part simulating high IOPs found in glaucoma and ocular hypertension. Inversion also simulates negative g-forces experienced in aerobatic maneuvers such as those produced during aerial combat. Studies using achromatic pattern-reversal visual evoked potentials (VEPs) have shown losses in response amplitude when subjects are inverted and IOP is increased. In other studies, chromatic, patternonset VEPs have been shown to be a sensitive and objective indicator of ocular and systemic pathology. Thus, chromatic pattern-onset VEPs may also show changes in amplitude and/or latency when subjects are subjected to full-body inversion. Methods In this study we employed chromatic, pattern-onset VEPs to determine if there were changes in response latency for the different visual pathways with healthy subjects during full-body inversion. Stimuli were 1 cpd horizontal sine-wave patterns presented in an onset mode (100 ms on/400 ms off). Subjects (n = 7) were tested at low to medium contrast levels, which were subjectively equated across chromatic pathways (S, LM, and achromatic). Patterns were presented using LCD goggles. Results All subjects showed a small but statistically significant increase in latency in the large negative component (CII) for both L-M and S-(L ? M) pathways during inversion. The achromatic pathway also showed a statistically significant increase in latency to the positive component (CI) during inversion. Conclusions These results demonstrate that changes in ocular and/or systemic physiology during full-body inversion can result in increased latencies of chromatic and achromatic pattern-onset VEPs.

Many insects can detect the polarization pattern of the blue sky and rely on polarization vision for sky compass orientation. In laboratory experiments, tethered Xying locusts perform periodic changes in Xight behavior under a slowly rotating polarizer even if one eye is painted black. Anatomical tracing studies and intracellular recordings have suggested that the polarization vision pathway in the locust brain involves the anterior optic tract and tubercle, the lateral accessory lobe, and the central complex of the brain. To investigate whether visual pathways through the anterior optic tract mediate polarotaxis in the desert locust, we transected the tract on one side and tested polarotaxis (1) with both eyes unoccluded and (2) with the eye of the intact hemisphere painted black. In the second group of animals, but not in the Wrst group, polarotaxis was abolished. Sham operations did not impair polarotaxis. The experiments show that the anterior optic tract is an indispensable part of visual pathways mediating polarotaxis in the desert locust.

The ascending thalamofugal visual pathway in pigeons (Columba livia) terminates in the telencephalic wulst. Characterizing the role of this pathway in visually guided behaviour has remained a challenge. To determine whether this pathway, and in particular the wulst, may participate in sun‐compass‐guided behaviour in homing pigeons, intact, ectostriatum‐lesioned or wulst‐lesioned pigeons were trained to use their sun compass to locate the direction of a food reward in an outdoor, octagonal arena. Control and ectostriatum‐lesioned pigeons learned the task well, and orientated appropriately during the first trial of the last three training sessions and after a phase‐shift manipulation. In contrast, the wulst‐lesioned pigeons learned the task but they took more sessions to learn, and their directional choices were more scattered during the first trial of the last three training sessions and after the phase‐shift manipulation. A subsequent regression analysis indicated that deeper layers...

This report is of a patient with an isolated sellar tuberculoma with suprasellar extension in association with thickening of the pituitary stalk who presented with signs and symptoms of hypopituitarism. Magnetic resonance imaging showed a sellar mass with suprasellar ...

We have analyzed the immunolabeling with the antibody RT97, a good marker for ganglion cell axons in several species, in the normal and regenerating visual pathways of teleosts. We have demonstrated that RT97 antibody recognizes several proteins in the tench visual system tissues (105, 115, 160, 200, 325 and 335 kDa approximately). By using immunoprecipitation and Western blot we have found that after crushing the optic nerve the immunoreactivity to anti RT97 increased markedly in the optic nerve. In immunohistochemical analysis we also found a different pattern of labeling in normal and regenerating visual pathways. In normal tench RT97 is a good marker for the horizontal cells in the retina, for growing ganglion cell axons which run along the optic nerve from the retina to the optic tectum and of the axon terminals in the stratum opticum and stratum fibrosum and griseum superficiale in the optic tectum. After optic nerve crush, no immunohistochemistry modifications were observed in the retina. However, in accordance with Western blot experiments, in the optic nerve intensely stained groups of regenerating axons appeared progressively throughout the optic nerve as far as the optic tectum. We conclude that the antibody RT97 is an excellent marker of growing and regenerating axons of the optic nerve of fish.