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At least 1,603 records · Page 89Linked to original sources
PubMed1996

Field of dreamers and dreamed-up fields: functional and fake perimetry.

PURPOSE: Hysterical and malingering patients can manifest visual field defects on perimetry (visual field testing), including defects suggestive of true visual pathway pathology. It has been shown that control subjects can easily imitate some pathologic defects with automated, computed perimetry. The authors sought to determine whether subjects could imitate the same pathologic defect with manual and automated perimetry. METHOD: Six subjects posed as patients with neurologic problems. They had manual perimetry with both an experienced and inexperienced technician followed by automated perimetry. They were later interviewed about the methods of the technicians and the difficulty of the exercise. RESULTS: Four of six subjects easily imitated the assigned defects with both technicians on manual perimetry and with automated perimetry. These included quadrantic, altitudinal, hemianopic, and enlarged blind-spot defects. Two subjects who were assigned cecocentral and paracentral scotomas instead produced enlarged blind spots by manual perimetry and defects suggestive of chiasmal pathology by automated perimetry. Paradoxically, some subjects found that experienced technicians were easier to fool than inexperienced technicians because of the systematic way in which experienced technicians defined defects. CONCLUSIONS: With minimal coaching, some subjects can imitate visual fields with enlarged blind spots, quadrantic, hemianopic, and altitudinal defects with ease and reproducibility by both automated and manual perimetry. Cecocentral and paracentral scotomas are harder to imitate but may be mistaken as representing chiasmal pathology. Paradoxically, experienced technicians may not be better at detecting hysterical or malingering individuals.

Adult↗
PubMed2001

Cortical areas related to attention to 3D surface structures based on shading: an fMRI study.

The aim of the present study was to determine which cortical areas are activated in relation to attention to a three-dimensional (3D) structure of a surface based on shading. Cortical activities were examined using functional magnetic resonance imaging while subjects discriminated whether the central part of the surface protruded or was recessed based on shading without any binocular disparity cues. Relatively broad cortical areas including both dorsal and ventral visual pathways were recruited when shading was used as a crucial cue for the perception of the 3D structure of a surface. In these cortical areas, however, the right intraparietal area was shown to be commonly activated in all subjects and in all sessions by multisubject conjunction analysis. These results strongly suggest that the intraparietal area plays an important role in perception of the 3D structure of a surface, even when based only on monocular depth cues without binocular disparity cues.

Adult↗
PubMed1986

Goldfish retina and tectum influence each other's growth activity during regrowth of the retinotectal projection.

Variations in retinal and tectal growth activity, during regrowth of the goldfish retinotectal projection, were monitored by measuring the rates of incorporation of [14C]leucine into soluble protein and tubulin-enriched fractions at different times after crushing the optic nerves. Other experiments tested for growth-modulating interactions between tectum and retina. Here we studied how the absence of one of these structures (i.e. tectal ablation or eye removal) affected the profile of biosynthetic activity in the other. Experiments were also conducted on groups of fish in which the tectum was reinnervated by a half-retina (either half-nasal (1/2 N) or half-temporal (1/2 T) retina). This was done to ascertain if growth interactions between retina and tectum display any position-dependent differences that may be relevant to retinotopic ordering during regeneration. Our studies have revealed that: the retina and tectum of 1/2 T and 1/2 N groups differ in their growth responses during regeneration of the visual pathway: the tectum may exert a stimulatory and at other times an inhibitory influence on retinal protein synthesis; and retina and tectum display a bimodal profile of biosynthetic activity during regeneration that coincides with two stages of increased cell division (primarily glia) which other workers have found occurs in the tectum and tract during regeneration of the retinotectal projection. Indeed it seems there may be a link between this glial proliferation and the neurotrophic and guiding influences which tectum and retina exert upon one another during regeneration.

Animals↗
PubMed1984

[Atlas of head anatomy in the neuro-ocular plane].

The "Atlas of cross-sectional orbito-cephalic anatomy in the neuro-ocular plane" does exist (now in press). The authors submit the main clinico-anatomical correlations observed. We will remind you that the "neuro-ocular plane" (N.O.P.) is defined as the C.T. plane of cephalic orientation comprising "both lenses, optic nerve heads and optic canals in the primary position of gaze". The more informative anatomical, radiological and anthropological data that could derive from the N.O.P. are stressed; first, we will evaluate the validity of our work and the problems we had while building the atlas; then we will describe briefly the position of this cephalic orientation plane as compared to other planes (specifically the anthropological baseline, the orbito-meatal line, the vestibular orientation etc...) previously described. Finally, we will end our discussion by giving the anatomical correlations obtained in the N.O.P.: this plane would best include all the visual pathways starting "from the cornea to the calcarine fissure"; it would also reflect the same orientation of the temporal horn of the lateral ventricle as well as the orientation of the lateral fissure. Much more, the orthogonality of this cephalic orientation to the direction of the brainstem is demonstrated, enhancing the accuracy of the three dimensional approach in the evaluation of the orbito-cephalic anatomy and diseases, as actually completed with C.T. and N.M.R. imaging, at the Centre National d'Ophtalmologie des XV-XX in Paris.

Anatomy, Artistic↗
PubMed1977

Analysis of chromatic-adaptation effect by a linkage model.

Hunt suggested that an adaptation-dependent linkage in the visual pathway from the retina to the brain can explain the variation of saturation produced by change of adapting luminance. If variation of saturation is caused by change of linkage, this change must also be involved in chromatic adaptation to light sources that have different chromaticities. By considering the effective adaptation levels of receptors, the model is extended and formulated for application to prediction of chromatic adaptation. It is tested by use of experimental results for chromatic adaptation obtained by Burnham et al. Suitable selection of parameters that specify the state of linkage produces good predictions of the effects of chromatic adaptation.

Adaptation, Ocular↗
PubMed2000

Organization of intratelencephalic projections to the visual Wulst of the chick.

The avian visual Wulst, said to be the equivalent of the striate cortex in mammals, is the telencephalic visual area of the thalamofugal visual pathway. In this study, by means of retrograde labelling with fluorescent tracers injected into the Wulst regions in the left and right hemispheres, we have investigated the organization of the intratelencephalic projections to the visual Wulst in chicks. After injecting Fluorogold (FG), True blue (TB) or rhodamine into the visual Wulst, fluorescent-labelled neurones were found in the ipsilateral neostriatum frontale, pars lateralis (NFl), the ipsilateral neostriatum intermedium (NI) and the ipsilateral dorso-lateral neostriatum. Labelled neurones were also found in both the ipsilateral and contralateral archistriata. In addition, some neurones in the archistriatum were double-labelled, which indicates that these archistriatal neurones have axon collaterals projecting to the visual Wulst on both sides of the forebrain. Through these intratelencephalic afferents to the visual Wulst, visual information transmitted in the thalamofugal pathway may be modulated by other telencephalic areas. The possible roles of these connections in regulating behaviour are discussed.

Animals↗
PubMed1993

Quantification of congruence between the right and left visual fields.

In the past, congruence between the right and left visual fields could only be evaluated subjectively. This study presents a congruence index to assess the similarity of the two visual fields objectively and quantitatively based on probability calculations. In 18 patients with suprachiasmal lesions of the visual pathways (cerebrovascular accident or tumor), the index found a homonymous congruence in all cases (100%). Of 26 persons with pituitary adenoma, in 22 cases (85%) the index found heteronymous congruence. The validity of the method may be even higher, because all cases with atypical indices also had atypical congruence by subjective evaluation. Using this new method in 41 patients with primary open-angle glaucoma, heteronymous congruence was detected in 73% and homonymous congruence was found in 17%. This new index may be useful for the development of computerized parametric methods of differential diagnosis.

Adult↗
PubMed1996

Distribution of visinin-like protein (VILIP) immunoreactivity in the hippocampus of the Mongolian gerbil (Meriones unguiculatus).

Visinin-like protein (VILIP) is a neuronal EF-hand Ca(2+)-binding protein. In the chick brain, it is widely expressed, e.g. in neurons of the visual pathway and the cerebellum. In the cerebellum, a presynaptic localization of VILIP in glutamatergic parallel- and climbing-fiber terminals has been observed. Here, we describe the distribution of immunoreactivity (IR) detected by antibodies against chick VILIP in the gerbil hippocampus at the light and electron microscopic level. VILIP antibodies stain neurons in the whole hippocampal formation including pyramidal cells in the CA1 and CA3 region of the Ammon's horn and granule cells of the dentate gyrus. In CA3 neurons, VILIP-IR is localized in dendrites and dendritic spines.

Animals↗
PubMed1976

Organization of the visual cortex: comparative anatomical and behavioral studies.

In all mammals there are two parallel visual pathways ascending to the cortex: the geniculostriate system and the tectopulvinar system. However, there is a difference among mammals in the locus and extent of the cortical target of the tectopulvinar path. In several diverse species such as squirrel and tree shrew the cortical target of the tectopulvinar system lies adjacent to area 17 and extends into the temporal lobe; but areas 18 and 19 do not receive fibers from the tectorecipient zone of the pulvinar in Galago and presumably in all primates. This anatomical difference may account for the drastic sensory effect of removing area 17 in primates, and the failure to find marked sensory changes in tree shrews or squirrels deprived of the geniculostriate system.

Animals↗
PubMed2004

Retina-driven dephosphorylation of the NR2A subunit correlates with faster NMDA receptor kinetics at developing retinocollicular synapses.

We describe a homeostatic mechanism that limits NMDA receptor currents in response to early light activation of a developing visual pathway. During the second postnatal week of rodent retinocollicular development, the Ca2+-activated phosphatase calcineurin (CaN) mediates a rapid, activity-induced shortening in the decay time of NMDA receptor (NMDAR) currents. We show that protein kinase A acts in opposition to CaN to maintain NMDAR currents with long decay times. The CaN-mediated change is coincident with the initial expression of the NMDAR subunit NR2A. Using NR2A knock-out mice and dialyzing neurons with a constitutively active CaN, we demonstrate that NR2A subunits are necessary for the effect of CaN on NMDAR current kinetics. In wild-type mice, Ser900 of NR2A, previously implicated in CaN-mediated glycine-independent desensitization, becomes chronically dephosphorylated by postnatal day 11 as NMDAR current decay times become faster. Pharmacologically disrupting early photoreceptor-driven activity in the retina eliminates the dephosphorylation of NR2A and prevents the shortening in NMDAR current decay time. These data suggest that the developmental onset of retinal activity increases CaN-mediated dephosphorylation of NR2A subunits newly incorporated into synaptic NMDARs of the superior colliculus, thereby providing a mechanism for the early and rapid reduction of NMDAR current decay time in visual neurons.

Animals↗
PubMed2004

Control of late off-center cone bipolar cell differentiation and visual signaling by the homeobox gene Vsx1.

Retinal bipolar cells are interneurons that transmit visual signals from photoreceptors to ganglion cells. Although the visual pathways mediated by bipolar cells have been well characterized, the genes that regulate their development and function are largely unknown. To determine the role in bipolar cell development of the homeobox gene Vsx1, whose retinal expression is restricted to a major subset of differentiating and mature cone bipolar (CB) cells, we targeted the gene in mice. Bipolar cell fate was not altered in the absence of Vsx1 function, because the pan-bipolar markers Chx10 and Ret-B1 continued to be expressed in inner nuclear layer neurons labeled by the Vsx1-targeting reporter gene, tauLacZ. The specification, number, and gross morphology of the subset of on-center and off-center (OFF)-CB cells defined by tauLacZ expression from the Vsx1 locus were also normal in Vsx1(tauLacZ)/Vsx1(tauLacZ) mice. However, the terminal differentiation of OFF-CB cells in the retina of Vsx1(tauLacZ)/Vsx1(tauLacZ) mice was incomplete, as demonstrated by a substantial reduction in the expression of at least four markers (recoverin, NK3R, Neto1, and CaB5) for these interneurons. These molecular abnormalities were associated with defects in retinal function and documented by electroretinography and in vitro ganglion cell recordings specific to cone visual signaling. In particular, there was a general reduction in the light-mediated activity of OFF, but not on-center, ganglion cells. Thus, Vsx1 is required for the late differentiation and function of OFF-CB cells and is associated with a heritable OFF visual pathway-specific retinal defect.

Animals↗
PubMed2003

Spatio-temporal dynamics of brain mechanisms in aversive classical conditioning: high-density event-related potential and brain electrical tomography analyses.

Social cognition, including complex social judgments and attitudes, is shaped by individual learning experiences, where affect often plays a critical role. Aversive classical conditioning-a form of associative learning involving a relationship between a neutral event (conditioned stimulus, CS) and an aversive event (unconditioned stimulus, US)-represents a well-controlled paradigm to study how the acquisition of socially relevant knowledge influences behavior and the brain. Unraveling the temporal unfolding of brain mechanisms involved appears critical for an initial understanding about how social cognition operates. Here, 128-channel ERPs were recorded in 50 subjects during the acquisition phase of a differential aversive classical conditioning paradigm. The CS+ (two fearful faces) were paired 50% of the time with an aversive noise (CS upward arrow + /Paired), whereas in the remaining 50% they were not (CS upward arrow + /Unpaired); the CS- (two different fearful faces) were never paired with the noise. Scalp ERP analyses revealed differences between CS upward arrow + /Unpaired and CS- as early as approximately 120 ms post-stimulus. Tomographic source localization analyses revealed early activation modulated by the CS+ in the ventral visual pathway (e.g. fusiform gyrus, approximately 120 ms), right middle frontal gyrus (approximately 176 ms), and precuneus (approximately 240 ms). At approximately 120 ms, the CS- elicited increased activation in the left insula and left middle frontal gyrus. These findings not only confirm a critical role of prefrontal, insular, and precuneus regions in aversive conditioning, but they also suggest that biologically and socially salient information modulates activation at early stages of the information processing flow, and thus furnish initial insight about how affect and social judgments operate.

Adolescent↗
PubMed1984

von Recklinghausen neurofibromatosis. II. Incidence of optic gliomata.

The association of optic glioma with von Recklinghausen neurofibromatosis (NF) is well established. However, the incidence of these tumors in a large population of NF patients, prospectively evaluated with modern radiologic techniques, has not been established. We investigated the ophthalmic and intracranial features of NF in 217 patients aged 4 weeks to 69 years, in whom the diagnosis was based on stringent criteria. Tumors at various locations along the anterior visual pathway occurred in 15% of patients and were occasionally bilateral. The mean age of patients with chiasmal tumors was approximately 15 years less than patients with tumors of the optic nerve only. Two-thirds (67%) of all tumors were neither suspected historically nor detected by ophthalmologic examination. Neither the ophthalmoscopic absence of optic atrophy nor the normal results of roentgenograms of the optic foramina were reliable predictors of tumors detected by CT scan. The presence of optic glioma is not correlated to other ocular, skeletal, neurologic, or anamnestic risk factors.

Adolescent↗
PubMed1998

Common reference frame for neural coding of translational and rotational optic flow.

Self-movement of an organism through the environment is guided jointly by information provided by the vestibular system and by visual pathways that are specialized for detecting 'optic flow'. Motion of any object through space, including the self-motion of organisms, can be described with reference to six degrees of freedom: rotation about three orthogonal axes, and translation along these axes. Here we describe neurons in the pigeon brain that respond best to optic flow resulting from translation along one of the three orthogonal axes. We show that these translational optic flow neurons, like rotational optic flow neurons, share a common spatial frame of reference with the semicircular canals of the vestibular system. The three axes to which these neurons respond best are the vertical axis and two horizontal axes orientated at 45 degrees to either side of the body midline.

Animals↗
PubMed1990

A stereoscopic view of visual processing streams.

Recent anatomical and physiological studies of the visual pathway suggest the existence of at least three parallel processing streams in the lateral geniculate/primary cortex structure--a magno/interblob stream for motion and transient information; a parvo/interblob stream for high spatial frequency, static information; and a parvo/blob stream for chromatic and low spatial frequency information. How does this functional typology relate to the processing for stereoscopic depth? Human stereopsis may be viewed as consisting of three distinct types of disparity processing: coarse, local stereopsis suitable for stereomovement processing by the magno/interblob stream; fine, global stereopsis suitable for the processing of complex random-dot stereograms by the parvo/interblob stream; and simple, protostereopsis for processing size differences between the two eyes by the parvo/blob stream. Extensive psychophysical evidence supports the identification of these three disparity processes with the three processing streams.

Color Perception↗
PubMed1978

The Pulfrich spatial frequency phenomenon: a psychophysical method competitive to visual evoked potentials in the diagnosis of multiple sclerosis.

The results of a study in which visual evoked responses (VERs) and a modified Pulfrich method were compared showed that both methods are very effective for the diagnosis of multiple sclerosis. With VERs, 97% of the multiple sclerosis cases were diagnosed correctly, while the corresponding value for the Pulfrich method was 93%. In contrast to VERs, the Pulfrich method allows only measurement of latency differences between the two visual pathways. This method involves measuring the speed required to cause a shift in the apparent depth location of a large, moving, striped pattern observed with a neutral density filter over one eye. A pathological transmission time was inferred when the patients observed a shift in the depth of the moving pattern either without any filter at all or with a filter whose attentuation was no more than 0.2 log units. A further criterion for pathology was a difference of more than 10% between the two eyes in the retinal speed required for a depth displacement using a 1.5 log unit filter. This test requires about 15 minutes, and can be carried out by a technical assistant.

Adult↗
PubMed1994

Directional selectivity in a nonspiking interneuron of the crayfish optic lobe: evaluation of a linear model.

1. Intracellular recordings, sine wave gratings, and paired flashes were used to characterize the directional selectivity (DS) of the peripheral neurons of the crayfish visual pathway. DS was observed in nonspiking tangential (Tan1) neurons of the distal medulla externa and it is expressed by the amplitude of the modulated synaptic potential elicited with drifting gratings. 2. The directional mechanism was characterized by variations in the grating contrast, spatial frequency, and temporal frequency. DS is both contrast and velocity dependent. 3. The velocity dependence of DS for fixed stimulus contrast can be described by a linear model including a delay and subtractive compare operation. This mechanism operates over the entire useful range of spatial and temporal frequencies. 4. The parameters of the linear model can be estimated from the spatiotemporal structure of the Tan1 cell receptive field. The receptive field exhibits a spatially asymmetric inhibitory subfield that is offset from the excitatory subfield by 3-5 degrees (1-2 ommatidia). The inhibition is delayed relative to excitation by 50-100 ms. 5. The contrast dependence of DS reflects an apparent nonlinearity in the mechanism that determines the null response amplitude. The preferred response magnitude is approximately linear with variations in contrast. 6. The nonlinearity observed in the null direction can in principle be attributed to either a tonic excitation at 0 contrast or a threshold for inhibition. There is evidence for both processes in the Tan1 cell visual response.

Acetylcholine↗
PubMed1988

Changes in rapidly transported proteins in developing hamster retinofugal axons.

Proteins synthesized in retinal ganglion cells and conveyed to the terminals of optic tract axons in the rapid phase of axonal transport were analyzed at different developmental stages in the hamster. Animals between 2 d of age and adulthood were labeled intraocularly with 35S-methionine, and after a 4 hr survival time, the superior colliculus was dissected out, subjected to subcellular fractionation, and radiolabeled proteins in the particulate fraction analyzed by 2-dimensional gel electrophoresis and fluorography. The previously identified growth-associated phosphoprotein, GAP-43 (GAP-48, B-50, F1, pp46), was synthesized and transported at high levels in the neonate, but these levels declined precipitously after the second postnatal week. Immunohistochemical studies using a monospecific antibody showed that GAP-43 was localized along the entire length of retinal axons in the optic tract and target areas in P2 animals but was virtually absent in the adult visual pathway. By metabolic labeling, 2 proteins with molecular weights of about 230 kDa also showed a sharp decrease during development. In contrast, acidic proteins of 27 and 64 kDa, which were barely detectable in the neonate, increased steadily to become the most heavily labeled proteins of rapid axonal transport by the second postnatal week. Another group of proteins, of about 94-110 kDa, also rose to peak levels after birth but then declined. Temporal correlations between the molecular changes described here and the known anatomical events in optic tract development suggest that the synthesis and transport of particular membrane proteins may be directly related to the sequence of morphological changes.

Animals↗