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PubMed1985

Somatostatin (SRIF)-like immunoreactivity in subcortical and cortical visual centers of the rat.

The distribution of neuronal elements containing immunoreactive somatostatin (I-SRIF) in the rat central visual pathway was examined by light-microscopic immunocytochemistry. These studies were concerned with the location and morphology of neurons and innervated cells and the distribution of fiber and terminal plexuses in the primary visual cortex (area 17), visual association areas 18 and 18a, the superior colliculus, the lateral geniculate nucleus, and the pretectum. In the superior colliculus, I-SRIF-containing fibers and perikarya were distributed predominantly in the superficial, or visual, layers; these elements were moderately dense and occupied the entire mediolateral extent of these layers. In the intermediate and deep layers, immunoreactive neurons were widely scattered, and fibers were located mainly in the medial third. Immunoreactive cell populations in the superior colliculus included small bipolar neurons with fusiform perikarya and multipolar neurons with round to ovoid perikarya. In the pretectum, the peptide was demonstrable in large and small multipolar neurons of the nucleus of the optic tract and in the posterior and olivary pretectal nuclei. I-SRIF-containing neurons were also present in the nucleus of the posterior commissure, the nucleus of Edinger-Westphal, and the ventral division of the lateral geniculate nucleus. In the visual cortex, the peptide was present in all layers and in a variety of morphologically defined cell populations, including some which are presumed excitatory (pyramidal and bipolar cells) and others which are presumed inhibitory (bitufted and stellate cells). Our data suggest that somatostatin is involved in visual and visuomotor reflex pathways and in the horizontal optokinetic nystagmus reflex pathway. These results provide a foundation for further studies to evaluate the role of this peptide in visual processes.

Animals↗

PubMedDate not supplied

The influence of fixational eye movements on the response of neurons in area MT of the macaque.

We analyzed the relationship between eye movements and neuronal responses recorded from area MT in alert monkeys trained to maintain visual fixation during the presentation of moving patterns. The monkeys made small saccades which moved the eyes with velocities that spanned the sensitivity range of MT neurons. The saccades evoked changes in the neuronal response that depended upon (1) the level of stimulus-evoked activity amidst which the saccade occurred and (2) the direction of the saccade relative to the preferred direction of the neuron. Most notably, saccades were able to suppress stimulus-evoked activity when they caused retinal image flow that opposed the neuron's preference and were able to elicit a response or enhance weak activity when they caused flow in the neuron's preferred direction. On average, the disturbance lasted 40 ms beginning about 40 ms following saccade onset. Using these parameters, we simulated synthetic spike trains from an imaginary pair of similarly tuned neurons and determined that the interneuronal correlation due to saccades should be negligible at all but the lowest ongoing firing rates. This conclusion was supported from our data by the observation that response variance for single MT spike trains was not measurably reduced during periods of stable gaze compared to periods when eye movement exceeded a stability criterion (0.1 deg during 0.5 s). While the intrusions caused by saccades are too short-lived and infrequent to account for the variability of MT neuronal response (counter to the finding in V1 of Gur et al., 1997), the clear directional signal that they carry in area MT suggests that motion perception is not blocked during saccades by suppression at early stages in the visual pathway.

Animals↗

PubMed2001

Visual evoked potentials in patients with psoriasis vulgaris.

PURPOSE: The aim of this study is an estimation of the visual evoked potentials (VEP) in patients with psoriasis vulgaris. The role of the nervous system was pointed out in the pathogenesis of psoriasis. Also epidemiologic research confirms that patients with psoriasis are at increased risk of MS development. MATERIALS AND METHODS: A group of 30 psoriatic males aged between 18 and 54 was examined. The results were compared with those obtained from a group of 30 healthy age-matched males and they were correlated with the psoriasis area and severity index (PASI), the skin surface area involved, duration of the disease and duration of the last relapse. In neurological and ophthalmological examinations no pathological symptoms were detected in either group. The VEP examination was executed using pattern reversal (pr) and pattern flash (pf) stimulation. RESULTS: Using pf stimulation, in the group of patients with psoriasis vulgaris, a statistically significant elongation in the latency of P-100 and reduction of response amplitude, not related to the PASI, nor the skin surface area involved, nor duration of the last relapse, were observed. CONCLUSIONS: The results of the study indicate subclinical damage of the visual pathway in patients with psoriasis vulgaris.

Adolescent↗

PubMed1996

Neuronal basis of amblyopia: a review.

Amblyopia is an acquired defect in vision due to an abnormal visual experience during a sensitive period of visual development. The neuronal basis of amblyopia is the study of the effects of "abnormal" environmental influences on the genetically programmed development of the visual processing system. Visual pathway development commences with ganglion cells forming the optic nerve. The process that guides these neurones initially to the lateral geniculate nucleus (LGN) and then onto the visual cortex is genetically programmed. Initially this process is influenced by spontaneously generated impulses and neurotrophic factors. Following birth, visual stimuli modify and refine the genetically programmed process. Exposure to the visual environment includes the risk of abnormal inputs. Abnormal stimuli disrupt the formation of patterned inputs allowing alteration of visual cortical writing with reduction in ocular dominance columns driven by the abnormal eye. Correction of the abnormal visual input and penalisation of the "normal" input is the mainstay of therapy for amblyopia. Further understanding of the mechanisms involved in the development of a normal visual processing system will allow trialing therapies for amblyopia not responding to occlusion therapy. Levodopa is one agent providing insights into recovery of visual function for short periods in apparently mature visual systems.

Amblyopia↗

PubMed1996

Clinical signs and symptoms requiring computed tomography and magnetic resonance imaging evaluation.

A summary of some of the clinically important symptoms and signs relating to disease of the afferent visual pathways, motility, and the orbit are presented. Common disorders are discussed in the context of choosing a neuroimaging study. Specific findings (e.g., pupillary abnormalities, types of nystagmus, visual field patterns) that may affect the type of study and the anatomic area that is imaged are emphasized.

Diagnosis, Differential↗

PubMed1996

A cell model for the detection of local image motion on the magnocellular pathway of the visual cortex.

We propose that five types of cell on the magnocellular pathway of the visual cortex constitute a function hierarchy for detecting local image motion. Lateral geniculate nucleus cells and two simple cell types analyse one-dimensional velocities perpendicular to oriented components within a moving stimulus. Combining these velocities, a group of complex cells along a sine wave fire over the cell array. The amplitude and phase of the wave correspond to the local motion's speed and direction. A motion-detection cell in the middle temporal area then extracts the wave of activated complex cells to detect the motion. Applying Hough and inverse Hough transforms and Reichardt's spatio-temporal correlation to the hierarchy, we modeled these cell types as a series of formulas that represent the synaptic functions of neurons. The modeled cells reflect the response to various stimuli in actual cells, and explain Adelson and Movshon's two-stage hypothesis neurophysiologically. The intersection-of-constraint-lines solution of the hypothesis is equivalent to the inverse Hough transform processed in motion-detection cells. We propose tests for validating this cell model using microelectrodes and optical imaging.

Geniculate Bodies↗

PubMed2003

Topographic organization of projections from the amygdala to the visual cortex in the macaque monkey.

The topography of amygdaloid projections to the visual cortices in the macaque monkey was examined by injecting the fluorescent tracers Fast Blue and Diamidino Yellow at different locations in the occipital and temporal lobes and mapping the distribution of retrogradely labeled cells in the amygdala. Injections involving regions from rostral area TE to caudal area V1 all resulted in labeled cells within the basal nucleus of the amygdala. Relatively few double-labeled cells were observed even when the two injections were separated by less than 3 mm. The projections were rostrocaudally organized such that projections to caudal visual areas originated from dorsal and caudal portions of the magnocellular division of the basal nucleus while projections to more rostrally situated visual areas originated in more rostral and ventral portions of the basal nucleus. When injections involved rostral and medial portions of area TE, retrogradely labeled cells were observed in the accessory basal and lateral nuclei in addition to the basal nucleus. These data confirm that the amygdala gives rise to feedback projections to all levels of the "ventral stream" visual pathway. The projections do not appear to be diffusely distributed since few double-labeled cells were observed. The largest cells of the basal nucleus, those located in the magnocellular division, project the farthest in the visual system and innervate all occipital and temporal levels. The smaller cells, in the intermediate and parvicellular regions, project to more rostral and medial portions of the visual cortex. These results suggest that the amygdala may have substantial modulatory control over sensory processing at all stages of the ventral-stream visual cortical hierarchy.

Amidines↗

PubMedDate not supplied

The evaluation of sellar region tumours with pattern visual evoked potentials.

Pattern visual evoked potentials (PVEPs) were performed on 20 patients with sellar tumours. The aim was to assess the validity of full-field PVEPs combined with a topographic recording in chiasmatic compression. They were abnormal in 95% of the patients, with variable patterns (absent or distorted responses). Our results show that PVEPs are very sensitive in revealing compression on visual pathways and that they correlate with the progression of the tumour. However, they are not reliable in detecting the chiasmatic or retrochiasmatic site of the lesion and relative visual field defect, because of the multidirectional extension of the tumour.

Adult↗

PubMed1988

[Role of specific and nonspecific afferent currents in forming evoked brain potentials to photic stimulation in the cat].

Evoked potentials during light stimulation were investigated in normal cats and after bilateral destruction of specific (the optical tracts, the lateral geniculate nuclei) and nonspecific (the brachia colliculi superioris) visual pathways. A component corresponding to the primary response was present in evoked potentials in all cases. It is concluded that photoinduced responses mainly depend on the quantity but not on the quality of the exciting afferent flow.

Afferent Pathways↗

PubMed1978

Interaction of chemosensory, visual, and statocyst pathways in Hermissenda crassicornis.

Neurons in the cerebropleural ganglia (CPG), photoreceptors in the eye, optic ganglion cells, and statocyst hair cells of the nudibranch mollusk Hermissenda crassicornis responded in specific ways, as recorded intracellularly, to stimulation of the chemosensory pathway originating at the tentacular chemoreceptors as well as to stimulation of the visual pathway originating at the photoreceptors. Synaptic inhibition of photoreceptors occurs via the chemosensory pathway. The possible significance of such intersensory interaction is discussed with reference to preliminary investigation of the animal's gustatory behavior and possible neural mechanisms of behavioral choice.

Animals↗

PubMed1995

Asymmetry of motion VEP in infantile strabismus and in central vestibular nystagmus.

Norcia et al. [1] 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 nystagmus) 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 180 +/- 20 degrees). 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.

Adolescent↗

PubMed1990

Neural contribution to spatiotemporal contrast sensitivity decline in healthy ageing eyes.

Contrast sensitivity thresholds were measured over a range of spatial and temporal frequencies in both a group of young and older observers. Results demonstrate a significant reduction in contrast sensitivity of the older age group at all but the lowest combinations of spatial and temporal frequencies investigated. The senile miosis and reduced optical transmission of the older eye was then mimicked using the younger observers as subjects. This combined effect of reducing retinal illumination produced no significant change in sensitivity. These findings are discussed in terms of neural loss within the visual pathways with increasing age.

Adult↗

PubMed2005

The nature of synthetic face adaptation.

Recent evidence demonstrates that adapting to a face will systematically bias the perception of faces that lie along the same identity trajectory in geometric face space but not faces that lie along different identity trajectories. We explored this configural aftereffect using synthetic face stimuli developed to measure face-specific processing. Adapting to synthetic "anti-faces" resulted in an identity-specific aftereffect that was characterized by a marked decrease in the slope of the psychometric functions. Adaptation transferred across different face sizes, but not different face viewpoints nor faces constructed about a non-mean face. Performance was captured by a model where responses were modulated through a divisive gain control and an additive constant reflecting a shift in the origin of perceived face space. Together, these results suggest that face adaptation reflects activity from mechanisms common to various processing stages along the visual pathway.

Adaptation, Biological↗

PubMed1996

Attentional modulation of visual motion processing in cortical areas MT and MST.

The visual system is constantly inundated with information received by the eyes, only a fraction of which seems to reach visual awareness. This selection process is one of the functions ascribed to visual attention. Although many studies have investigated the role of attention in shaping neuronal representations in the visual cortex, few have focused on attentional modulation of neuronal signals related to visual motion. Here we report that the responses of direction-selective neurons in monkey visual cortex are greatly influenced by attention, and that this modulation occurs as early in the cortical hierarchy as the level of the middle temporal visual area (MT). Our finding demonstrates a stronger and earlier influence of attention on motion processing along the dorsal visual pathway than previously recognized.

Animals↗

PubMed1982

Clinical and experimental evidence that the pattern electroretinogram (PERG) is generated in more proximal retinal layers than the focal electroretinogram (FERG).

A TV monitor was used to evoke either a pattern ERG to a contrast-reversing checkerboard (PERG), or a focal ERG to alternate increases and decreases of luminance of the blank screen within a bright surround (FERG). Both responses are small (approx 2 microV) and fast (approx 50 msec to peak) and are similar in several other properties. However, they differ in timing and respond differently to changes in contrast. Each frame of a TV picture evokes a "raster ERG," even though the screen is blank. The response is focal and specific to a small central strip of the screen. It is simpler to record than the FERG, where the whole screen is flashing. Because the FERG summation area is about 4 deg, small squares (checks) reversing in contrast produce little luminance response. In 5 of 7 cases where the PERG is unilaterally reduced, the FERGs or raster responses were not affected. Thus clinical evidence also suggests that the PERG may be a separate phenomenon to the FERG and produced at a different site. Toxic, traumatic, congenital, and degenerative diseases of the optic nerve reduce the PERG. The comparison is most easily made in unilateral disease. Ten weeks after an optic nerve insult, the PERG becomes reduced in the affected eye as if retrograde degeneration was occurring. In 27 amblyopes of various types, the PERG was reduced in 23 where orthoptic treatment had failed. In 4 patients responding to treatment, PERGs of the amblyopic eye were as large as, or larger than, those of the fellow eye. The loss is greater with smaller checks. Retinal changes do occur after age 4 but so slowly that responses in heavily occluded eyes are not reduced. An additional level in the visual pathway is thus accessible to evoked potential investigation.

Amblyopia↗

PubMed1984

Enhanced regional uptake of 2-deoxy-D-[14C]glucose in focal herpes simplex type 1 encephalitis: autoradiographic study in the rat.

We used the 2-deoxy-D-[14C]glucose (14C-DG) quantitative autoradiographic method to assess regional glucose metabolism in rats with focal herpes simplex virus type 1 (HSV-1) encephalitis. High 14C-DG uptake was detected in infected brain structures of both immunocompetent and immunosuppressed animals, likely as a result of increased glucose utilization by infected glia and neurons. Inflammatory infiltrates did not show augmented 14C-DG tissue uptake, and indeed regional isotope uptake declined in the later stages of infection as viral replication waned and necrosis developed. 14C-DG uptake was also depressed in uninfected brain regions that received afferents from the infected visual pathway.

Animals↗

PubMed2004

[Peculiarities of cytochrome oxidase activity in the visual cortex neurons of kittens reared under the conditions of flickering illumination].

The objective of this study was to analyze the influence of the light flickering with the frequency of 15 Hz, on the neuronal metabolic activity in kittens reared under the conditions of mesopic illumination. The method for demonstration of a respiratory enzyme cytochrome oxidase was used to study the visual cortex areas 17 and 18 and the lateral geniculate nucleus. It was shown that in kittens that were subjected to this stimulation as opposed to intact animals and to kittens reared under the conditions of mesopic illumination, specific changes in pattern of cytochrome oxidase distribution in area 17 took place. This change was manifested by the appearance of alternating zones of increased and decreased enzyme activity in layers III and IV. Within the cortical area 18 and lateral geniculate nucleus, no changes in the pattern of cytochrome oxidase activity distribution were detected in experimental kittens. It is suggested that flickering illumination results in disequilibrium of Y- and X-visual pathway activity.

Animals↗

PubMed1993

The isolated and perfused brain of the guinea-pig in vitro.

We describe here an isolated and perfused in vitro adult guinea-pig whole brain preparation which is an extension of the previously described in vitro brainstem-cerebellum preparation. Viability was tested by the analysis of trans-synaptic responses along the visual pathways following the electrical stimulation of the optic nerve or the optic radiations. The evoked field potentials were recorded in the dorsal lateral geniculate, the superior colliculus and the visual cortex. The distribution of extracellular currents was studied using current source density analysis, in order to determine the amplitude, time course and spatial organization of the synaptic activity at these sites. The study indicates that field potentials were very similar to those described in vivo. These data demonstrate the survival of a complex adult sensory system in vitro and suggest that this preparation can be used for the analysis of multisynaptic circuits in the mammalian brain.

Animals↗