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PubMed1999

Effect of the group II metabotropic glutamate agonist, 2R,4R-APDC, varies with age, layer, and visual experience in the visual cortex.

Group II metabotropic glutamate receptors (mGluR 2/3) are distributed differentially across the layers of cat visual cortex, and this distribution varies with age. At 3-4 wk, mGluR 2/3 receptor immunoreactivity is present in all layers. By 6-8 wk of age, it is still present in extragranular layers (2, 3, 5, and 6) but has disappeared from layer 4, and dark-rearing postpones the disappearance of Group II receptors from layer 4. We examined the physiological effects of Group II activation, to see if these effects varied similarly. The responses of single neurons in cat primary visual cortex were recorded to visual stimulation, then the effect of iontophoresis of 2R,4R-4 aminopyrrolidine-2, 4-decarboxylate (2R,4R-APDC), a Group II specific agonist, was observed in animals between 3 wk and adulthood. The effect of 2R, 4R-APDC was generally suppressive, reducing both the visual response and spontaneous activity of single neurons. The developmental changes were in agreement with the immunohistochemical results: 2R, 4R-APDC had effects on cells in all layers in animals of 3-4 wk but not in layer 4 of animals >6 wk old. Moreover, the effect of 2R, 4R-APDC was reduced in the cortex of older animals (>22 wk). Dark-rearing animals to 47-54 days maintained the effects of 2R, 4R-APDC in layer 4. The disappearance of Group II mGluRs from layer 4 between 3 and 6 wk of age is correlated with the segregation of ocular dominance columns in that layer, raising the possibility that mGluRs 2/3 are involved in this process.

Aging↗

PubMed1995

The visual system of the Florida garfish, Lepisosteus platyrhincus (Ginglymodi). IV. Bilateral projections and the binocular visual field.

Infusion of cobaltous-lysine into the optic nerve of juvenile Florida garfish reveals that the preoptic area, pretectum, thalamus and the mediorostral and ventrolateral poles of the optic tectum each receive bilateral, monosynaptic input. The bilateral input to the mediorostral pole of the tectum projects via the dorsal optic tract and terminates in the rostral half of the tectum. The bilateral input to the ventrolateral tectum projects via the ventral optic tract and extends the whole length of the tectum. The incidence of direct ipsilateral input to the tectum suggests binocular vision may play a functional role in the survival of this species. In order to test this hypothesis, we examined the retinal distribution of ipsilateral retinal ganglion cells that project to the mediorostral tectum and the size and location of the binocular visual field. Cell distribution was examined by retrograde labelling with rhodamine-conjugated dextran amine delivered by microinjections into the mediorostral pole of the right optic tectum. In the ipsilateral retina, ganglion cells are distributed in a narrow temporoventral area with a mean of 0.44 +/- 0.14 x 10(3) cells per mm2 apposing the retinal margin. In the contralateral retina, ganglion cells are also distributed within this temporoventral region with a mean peak density of 2.33 +/- 0.47 x 10(3) cells per mm2. Three broad classes of ipsilaterally projecting retinal ganglion cells (orthotopic cells within the ganglion cell layer, displaced cells within the inner nuclear layer, and giant cells within the ganglion and inner nuclear layers) are identified, intermingled in both the ipsilateral and contralateral retinae after retrograde labelling from the mediorostral pole of the tectum. Ophthalmoscopic mapping of the monocular and binocular visual fields reveals two small frontal wedges of binocular overlap. A dorsal wedge (12 degrees wide) extends from approximately 7 degrees above the horizontal axis to 10 degrees beyond the vertical axis, and a ventral wedge (20 degrees wide) extends approximately 10 degrees below the horizontal axis to 15 degrees beyond the vertical axis. The dorsal binocular visual field is subtended by the temporoventral region of the retina possessing both ipsilaterally and contralaterally projecting ganglion cells which terminate in the mediorostral pole of the optic tectum. Therefore, the partial decussation of retinal ganglion cell axons at the optic chiasm brings information from corresponding regions of the binocular visual field into register in the mediorostral pole of the optic tectum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2000

Modulation of neural activities during visual processing in the human extrastriate visual cortex.

Magnetoencephalographic responses to single letters (Japanese monosyllabic characters) presented in the left visual field were measured during visual cognition tasks, in which subjects judged matching of characters in two different processes based on phonological and graphical cues. Equivalent current dipoles, which represent focal neural activities, were localized in the extrastriate visual cortex of the occipital to occipitotemporal regions. The main activities were observed in the right lateral area when the subjects detected shape, and also in the medial and inferior areas of both hemispheres when they detected rhyme. These results suggest that the neural activities in the extrastriate cortex, which are related to early processing of familiar visual forms, can be modified by the top-down control.

Adult↗

PubMed2005

Orientation selectivity without orientation maps in visual cortex of a highly visual mammal.

In mammalian neocortex, the orderly arrangement of columns of neurons is thought to be a fundamental organizing principle. In primary visual cortex (V1), neurons respond preferentially to bars of a particular orientation, and, in many mammals, these orientation-selective cells are arranged in a semiregular, smoothly varying map across the cortical surface. Curiously, orientation maps have not been found in rodents or lagomorphs. To explore whether this lack of organization in previously studied rodents could be attributable to low visual acuity, poorly differentiated visual brain areas, or small absolute V1 size, we examined V1 organization of a larger, highly visual rodent, the gray squirrel. Using intrinsic signal optical imaging and single-cell recordings, we found no evidence of an orientation map, suggesting that formation of orientation maps depends on mechanisms not found in rodents. We did find robust orientation tuning of single cells, and this tuning was invariant to stimulus contrast. Therefore, it seems unlikely that orientation maps are important for orientation tuning or its contrast invariance in V1. In vertical electrode penetrations, we found little evidence for columnar organization of orientation-selective neurons and little evidence for local anisotropy of orientation preferences. We conclude that an orderly and columnar arrangement of functional response properties is not a universal characteristic of cortical architecture.

Action Potentials↗

PubMed1979

Visual-field asymmetries in letter recognition: evidence for asymmetry in early visual registration.

Two experiments on visual-field differences in tachistoscopic letter recognition are described. In the first, a bright pre-exposure field with a black fixation point was used, and the conventionally expected dominance of the right visual field was found. However, a large number of "blank" trials were observed, in which subjects completely failed to detect the presence of the flashed target. These "blanks" were themselves significantly asymmetric between visual fields, suggesting that asymmetry in early stimulus registration may play an unsuspected role in typical measures of cerebral asymmetry in recognition accuracy. This was confirmed in a second experiment in which use of dark pre-exposure fields eliminated "blanks" and led to higher over-all accuracy, with no visual-field differences. Implications for interpretation of laterality data with normal subjects are discussed.

Adult↗

PubMed1992

[Visual recognition processes in monkeys and their neuronal correlates in the visual cortex: the effect of an M-cholinoreceptor blocker].

Unit activity was studied in the visual cortex prior to and after amyzyl administration in monkeys trained for delayed visual differentiation of different colour stimuli. The data obtained suggests that the cholinergic mechanisms of the visual cortex are involved in the visual recognition and seem to play different functional roles at different stages of the behaviour.

Acoustic Stimulation↗

PubMed2004

[Visual search training for a case of homonymous field defect with multiple visual dysfunctions].

A 72-year-old right handed man developed right homonymous hemianopia without macular sparing, left homonymous lower quadranopia with macular sparing, cerebral amblyopia, cerebral achromatopsia, impaired form vision, and mild right hemispatial neglect, after multiple cerebral infarctions, involving bilateral occipital cortices. His intelligence and memory were deteriorated moderately. He failed to notice objects located in the affected visual field, because of his severely impaired visual search. When ordinary lighting was used, he showed severe right-sided omissions on the line cancellation test. However, omissions were less marked under the brighter lighting. By using a modified method of Kerkhoff and Vianen (1994), he was trained to make saccadic eye movements toward affected regions to find a target and to search and point at targets arranged randomly. As the sensitivity for contrast of isoluminante red and green stimuli was preserved well at high spatial frequencies despite the decreaced contrast sensitivity for brightness, we used green targets as the training stimuli. After the training, search field and pointing range that could be covered by the patient increased in size for both green and white targets, and daily activities improved. Moreover, after the training, he no longer showed discrepancy in line cancellation performances between ordinary and brighter lighting conditions. In the follow up period, the search field and the performance on the line cancellation test were maintained, while the performance of pointing targets array declined. The family members complained of mild re-deterioration of daily activities. Then, the training for searching and pointing re-introduced at home. After the training, his pointing performance and daily activities, evaluated by questionnaires to his family members, improved again. In conclusion, it was suggested that disordered visual search after a homonymous field defect can be treated effectively, even if multiple visual dysfunctions were associated.

Aged↗

PubMed1987

Glucose utilization of visual cortex following extra-occipital interruptions of the visual pathways by tumor. A positron emission tomography study.

To assess the effect of extra-occipital lesions on the local cerebral glucose utilization of the primary and associative visual cortex, 29 patients were studied in the unstimulated state by positron emission tomography and [18F]2-deoxyglucose. Quantitative Goldmann perimetry was done in each patient at the time of the positron emission tomographic study. Nine patients showed homonymous defects, either hemianopsia or quadrantanopsia, whereas nine patients had heteronymous defects. Eleven control subjects, free of any neurological symptoms and with normal visual fields, were also studied with [18F]2-deoxyglucose positron emission tomography. In the normal control subjects and in patients with a heteronymous defect, left-to-right differences in the local cerebral metabolic rate for glucose of the visual cortex varied less than 10%. In patients with hemianopic defects, differences ranged from 8 to 38%, with the hypometabolic cortex always contralateral to the field defect. In patients with quadrantanopic defects, the visual cortex contralateral to the field defect demonstrated differences from 14 to 24% above and below the calcarine fissure, the cortex that received greater input from the affected field being hypometabolic.

Adult↗

PubMed1987

[Response of neurons of the visual cortex (area 18) to extraocular proprioceptive stimulation: development in normal or dark-reared cats and interaction with visual activity].

Single unit responses to stimulation of the extraocular muscle receptors or of their afferent fibers were recorded from the visual cortical area 18 in normally or dark-reared cats. These responses were improved by a random visual stimulation delivered during the test. These proprioceptive responses, elicited with or without random visual activation, changed with age and as a function of the postnatal rearing conditions. In the normally-reared group, neurons which were activated by stimulation of the afferents from the Obliquus inferior displayed a preferred orientation for visual stimulus oriented at right angle to action plane of this particular muscle.

Aging↗

PubMed1988

Space-variant visual processing: spatially limited visual channels.

A multichannel model incorporating visual inhomogeneity is presented in this paper. The parameters that describe inhomogeneity have been experimentally obtained both at threshold and in several suprathreshold conditions. At threshold, probability summation is taken into account in order to determine the spatial extent of visual channels from experimental data showing an asymptotic increase in sensitivity with increasing grating area. At suprathreshold contrast, the region where luminance variations at several scales are visible has also been found. The results support a spatially limited multichannel model of early visual processing and set out a basis for studying perceptual phenomena from the viewpoint of linear space-variant visual processing.

Contrast Sensitivity↗

PubMed1988

[A study of visual function in congenital nystagmus--mechanism of visual improvement after stereotactic superior colliculectomy].

The clinical features of congenital nystagmus (CN) were studied statistically in 106 cases of CN. The point of the nystagmus at which the patients could best see the targets was detected in some patients. The effects of superior colliculectomy on their visual disturbance and the mechanism will be discussed. The study population comprises 106 patients, 79 males and 27 females, aged from one to 64 (mean 19.4 years). Patients with jerky type classified on ENG were found in 53 cases (50%), pendular type in 39 cases (37%), and mixed type in 14 cases (13%). Patients with jerky type showed significantly good visual acuity (mean 0.69 +/- 0.31, p less than 0.005). They showed significant abnormalities during pregnancy and delivery (p less than 0.01) and had a neutral point (p less than 0.01). Patients with pendular type, on the other hand, showed poor visual acuity (mean 0.26 +/- 0.30) and had significant frequency of family history (p less than 0.05), head tremor (p less than 0.01) and strabismus (p less than 0.01). Thirteen cases (12%) had ocular diseases which involved the retina, cornea and optic nerve. Visual function was elaborated on such parameters of ENG as perception, peak variation and plateau time. Perception, which means the ability to detect the dim flashes during the appearance of the nystagmus, was manifested by pushing a button when patients could detect flashes presented at random on the screen. At the turning point from the quick phase to the slow phase, the detection was executed most successfully. It is thought that in CN, a target is usually gazed upon at a point, changing the direction from the quick phase to the slow phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMedDate not supplied

[Glutamate decarboxylase activity in subcellular fractions of tissue of brain visual analyzer of dogs subjected to visual deprivation].

Glutamate decarboxylase activity in fractions of mitochondria, synaptosomes and membranes fragments of tissues brain visual analyzer central structures of the dog was found to decrease during visual deprivation. A degree of the decrease is different and depends on the deprivation duration. During a 45-day deprivation the specific activity of the enzyme lowers significantly in all subfractions, decrease is especially sharp in subfractions of heavy synaptosome and membranes (by 71-85%). The decrease in the activity is more pronounced in the anterior corpora bigemina and in external geniculate body than in the cortex visual area (field 17). During a 90-day deprivation the activity lowers in all the structures but to a less extent than during the 45-day deprivation. The specific activity in subfractions of heavy and light synaptosomes is 40-67% lower than normal and in the membrane and mitochondrial subfractions differs slightly. In the visual deprived dogs the intensity of GABA formation reduces in all the subfractions, the decrease being higher during the 45-day deprivation.

Animals↗

PubMed1982

The effects of early visual experience followed by prolonged dark rearing on visual cortex cells of cats.

Five groups of kittens (N = 13) were dark reared for 9.5-20 months following normal binocular exposure of 0-85 days after natural eye opening and 1 month of monocular deprivation. For comparison, kittens monocularly deprived (MD) for 10 months (N = 2) and normal adult cats (N = 13) served as controls. The ocular dominance distribution of cortical cells showed a clear (although small) bias in the first group of kittens which received the minimal exposure. A striking effect was obtained in the proportion of visually unresponsive cells (55.1%) in this first group of cats. Concerning orientation and direction selectivity, the highest proportions of nonselective cells, 16.1% and 33.3%, were obtained in the first two groups of cats respectively. It was concluded that periods of monocular deprivation shorter than that used in the present study (4 weeks) and without any previous visual experience would be ineffective if followed by a year or more of total absence of visual experience. Prolonged dark rearing therefore, masks the effect of prior monocular deprivation to a large extent. In addition, the results emphasize the fact that the age factor is more important than the duration of the monocular visual experience.

Aging↗

PubMed1996

Objective measurement of contrast sensitivity and visual acuity with the steady-state visual evoked potential.

Since the appearance of Campbell and Maffei's and Harter and White's reports it has been well established that the visual evoked potential (VEP) can be used to predict psychophysical contrast sensitivity and visual acuity and is thus suited as an objective technique to assess these fundamental aspects of vision. Nevertheless, the technique has not become a standard diagnostic tool, being too time-consuming to apply and suffering from variable reliability under pathological visual conditions. In addition, there are problems of reliability in normal subjects. By using an unconventional stimulus--temporally sinusoidal 16-Hz on-off modulation of sinewave gratings--we demonstrated that these problems can be alleviated in normal subjects. This stimulus avoids the low signals in the visible range that frequently occur with conventional pattern-reversal stimuli, it leads to high correspondence between normal observers, and it is much faster to apply than are transient VEPs. Initial applications of this stimulus to amblyopes yielded promising results. The steady-state VEP could consequently turn into a viable diagnostic procedure in disturbances of visual contrast perception.

Contrast Sensitivity↗

PubMedDate not supplied

[Informative value of forms of visual evoked potentials in assessing the location of a visual tract block].

It is proposed the explanation of the form of visual evoke potential (VEP) on the base of physical imagination of the electrical field of double electrical layers that can approximate the wave of excitement of the visual tract. We mast take into consideration the electrical potential as active as indifferent electrode simultaneously and estimate visual evoke potential as diversity. It is shown on mathematical model the more smooth form of visual evoke potential under block and unimportant to arrangement of the electrode over the place of block.

Evoked Potentials, Visual↗

PubMed1996

A dynamic and quantitative study of pattern visual evoked potentials and gamma-aminobutyric acid neurones in the lateral geniculate nucleus and the visual cortex of monocular deprivation cats.

PURPOSE: To assess the effects of monocular lid closure during critical period on cortical activity. METHOD: Pattern visual evoked potentials (PVEP) of the normal and the monocular deprivation (MD) cats were dynamically measured and the number of gammaaminobutyric acid immunopositive (GABA-IP) neurones of the area 17 of the visual cortex and the lateral geniculate nucleus (LGN) was quantitatively compared by using immunohistochemical method (ABC). RESULTS: The amplitude of the N1-P1 attenuated in deprived eyes (DE), NE/DE at postnatal week (PNW) 7-8 (P < 0.05), NE/DE at PNW 15-16 (P < 0.01); while P1 latency delayed, NE/DE at PNW 7-8 (P > 0.05), NE/DE at PNW 15-16 (P< 0.05). The numbers of GABA-IP neurones in layer A1 of the ipsilateral LGN and in layer A of the contralateral LGN, compared to those in the corresponding normal laminae, were not significant at PNW 7-8 and PNW 11-12 (P > 0.05), while in the same cats a reduction in the number of GABA-IP neurones was found in layer IV of area 17 at PNW 11-12 (P < 0.05). However, with longer survival of 3-4 weeks in duration, the numbers of GABA-IP neurones in the deprived laminae of LGN were remarkably reduced (P < 0.05). CONCLUSIONS: The amplitude of N1-P1 components is sensitive to the effects of monocular deprivation. Monocular deprivation in cats during critical period leads to dramatic changes of the number of GABA-IP neurones in the LGN and cortical layer IV receiving inputs from the deprived eye in cats. The deprivation-induced reduction in GABA-IP neurones is delayed in the LGN compared with the visual cortex. PVEP of the MD cats is consistent with the damage of its GABA system in visual cortex.

Animals↗

PubMedDate not supplied

Visual processing of configuration-dependent spatial characteristics of shapes and patterns. A model useful in the study of the role of the departure from circularity or dispersion of shapes in human visual perception.

In this work a theoretical model was used in combination with testings on normal subjects to get more insight in the role of the departure from circularity or dispersion of the shapes in visual perception. The model was inspired by the observation that the intensity of the effect of a given level of contrast of a shape usually increases, for the same area, with the shape being better concentrated around a center. The model introduces as a measurable characteristic the degree of concentration or dispersion of a shape with respect to a center. The measure was based on the maximum of the convolution integral of the characteristic function of the shape with the weighting function 1/2 pi r, r being the distance between the point of convolution and the surface element to be integrated. A program for the calculation of the degree of concentration of figures and other related processing operations was developed in Turbo Pascal language on a 486 PC. The program included the possibility to generate various figures and to operate on them various transformations such as strangulation, fragmentation with separation of fragments. The model introduces a center of the figure, the point best surrounded by the whole figure, with a geometric and visual significance, as resulting from the good concordance between its calculated and perceived positioning in different relatively simple shapes. In symmetrical compact figures subjected to a central separation or narrowing two centres appear entering the two resulting nuclear parts; a good concordance between model and perception was again observed in this transition to two centres and their subsequent positions in the two nuclear parts. In accord to model prediction, testings showed a very pronounced dependence of the summation efficiency over a contrasting area on the degree of dispersion of the area. This is reflected in the drastic decrease upon figure dispersion of the intensity with which a given brightness or colour contrast is perceived. Thus, the model gives a better explanation and a more efficient way to approach the great capacity of the visual system to disclose more compact shapes or agglomeration zones in a complex visual scene. This capacity is to a large extent due to the increase in the intensity with which a given contrast is perceived, occurring in these conditions. This intensity, which strongly depends on the degree of concentration or dispersion of the figure, becomes an important additional signal leading to the accentuation of the difference between compact and rarefied shapes. The model based on the degree of concentration determined around a centre, although useful for finding a centre and applicable satisfactorily to many shapes, do not cover well all aspects of shape dispersions. In shapes without a dominant central part the confrontation model-testing showed an important involvement in global perception of all local concentrations, not only central but also peripheral, the later underestimated in our model. The model can be however improved by taking into account also such local concentrations.

Form Perception↗

PubMed1982

Asymmetry and ventral course of the human geniculostriate pathway as determined by hippocampal visual evoked potentials and subsequent visual field defects after temporal lobectomy.

Twenty-two patients with psychomotor epilepsy were implanted with depth electrodes along the axis of the mesial temporal lobe to identify an operable unilateral epileptic focus. Neuronal and field potentials were recorded in response to diffuse retinal illumination and clear short-latency responses were found in parahippocampal gyrus. These visual afferents in the mesial temporal lobe are assumed to be both from subcortical and cortical visual areas. There was a clear asymmetry in the ventral trajectory of the geniculostriate pathway as evidenced by asymmetric neuronal and field potential responses to brief flashes in right vs. left hippocampal gyrus and confirmed by a corresponding partial visual field deficit following therapeutic anterior temporal lobectomy. These results demonstrate that there is a retinotopic organization of fibers in the human geniculostriate pathway and that this pathway may have considerable variability in the anterior and ventral course these fibers take through the temporal lobe. These findings adequately account for the presence of direct projections from geniculate to hippocampal cortex and for unexpected hemianopsias with standard resections of the temporal lobe when there is a deviant detour of the geniculostriate pathway.

Dominance, Cerebral↗