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PubMed1995

Projections from the visual areas to the neostriatum in rats. A re-examination.

Neostriatal afferents from the primary visual cortex in rats were studied using dextran-biotin, biocytin, and Fluoro-Gold. The area V1 was found to project only to a dorsomedial, longitudinal region of neostriatum (NS), bordering on the lateral ventricle and subcortical white matter. The preterminal fibres in the NS form fluffs which increase in number and density in the cases with larger injections. This target region is poorly stained for calbindin and yet belongs to the matrix compartment. The secondary visual areas also project to the dorsomedial NS region but they also innervate the deeper tissue in the same general region. Iontophoresis of Fluoro-Gold into the dorsomedial NS labelled some pyramidal neurones in the fifth layer of the primary visual cortex. The cortical areas that surround the visual cortical complex project to other regions of the NS: the somatosensory cortex to a dorsolateral longitudinal region and the auditory area to the medial half of the caudalmost portion of NS. Thus, major sensory cortical divisions project to non-overlapping NS regions. Since NS in monkeys and cats does not receive afferents from the primary visual cortex and in a number of other species does, we conclude that visual systems in different mammals differ with respect to their projections to NS.

Animals↗
PubMed1999

Dark rearing blocks the developmental down-regulation of brain-derived neurotrophic factor messenger RNA expression in layers IV and V of the rat visual cortex.

In this study, we describe the distribution of brain-derived neurotrophic factor messenger RNA in the binocular primary visual cortex of the rat during postnatal development, starting at postnatal day (P) 13. High-resolution non-isotopic in situ hybridization combined with Nissl staining were used to quantify the number of cells expressing brain-derived neurotrophic factor messenger RNA. At P13, most of the cells express brain-derived neurotrophic factor messenger RNA. After eye opening (P14-P15), the relative number of brain-derived neurotrophic factor messenger RNA-positive cells decreases by a factor of two in layer IV, i.e. that receiving the visual input, and in layer V. To verify the hypothesis that light could trigger this decrease, pups were kept in complete darkness from birth. At P22, pups reared in the dark were killed and the visual cortex processed for in situ hybridization and northern blotting. The results obtained in dark-reared animals prove that light deprivation can: (i) decrease the general levels of brain-derived neurotrophic factor messenger RNA, and (ii) increase the relative number of brain-derived neurotrophic factor messenger RNA-positive cells in layers IV and V with respect to control rats. Exposure to light for five days after the period of darkness restored the number of brain-derived neurotrophic factor messenger RNA-positive cells. We conclude that the expression of brain-derived neurotrophic factor messenger RNA in the rat primary visual cortex is regulated during development and that this process is under the control of visual input.

Animals↗
PubMed2003

Mapping multiple features in the population response of visual cortex.

Stimulus features such as edge orientation, motion direction and spatial frequency are thought to be encoded in the primary visual cortex by overlapping feature maps arranged so that the location of neurons activated by a particular combination of stimulus features can be predicted from the intersections of these maps. This view is based on the use of grating stimuli, which limit the range of stimulus combinations that can be examined. We used optical imaging of intrinsic signals in ferrets to assess patterns of population activity evoked by the motion of a texture (a field of iso-oriented bars). Here we show that the same neural population can be activated by multiple combinations of orientation, length, motion axis and speed. Rather than reflecting the intersection of multiple maps, our results indicate that population activity in primary visual cortex is better described as a single map of spatiotemporal energy.

Animals↗
PubMed1997

Magnocellular and parvocellular visual pathways are both affected in a macaque monkey model of glaucoma.

PURPOSE: Neurochemical changes in nerve cells were investigated in the lateral geniculate nucleus (LGN) and primary visual cortex of macaque monkeys with experimentally induced glaucoma. METHODS: Glaucomatous damage was induced in one eye of experimental animals by elevation of intraocular pressure following laser burns to the trabecular meshwork. Staining for the metabolic marker cytochrome oxidase, as well as immunolabelling for the neuronal markers synaptophysin and neurofilament proteins, was conducted on sections of the LGN and primary visual cortex. RESULTS: In the LGN, staining for cytochrome oxidase and immunolabelling for synaptophysin were reduced in the parvocellular and magnocellular layers that received input from the glaucomatous eye and neurofilament protein labelling was reduced in the parvocellular layers. Cytochrome oxidase staining demonstrated the presence of denervated ocular dominance columns in layer IVC of the primary visual cortex of experimental animals. CONCLUSIONS: Pre- and post-synaptic neurochemical alterations in the magnocellular and parvocellular visual pathways of the brain are associated with experimentally induced glaucoma in macaque monkeys.

Animals↗
PubMed1982

Single unit receptive fields in rabbit primary binocular cortex.

The receptive fields of 125 single units recorded from the binocular region of rabbit primary visual cortex have been analysed. The population of 43% radially symmetric, 23% directional, and 23% orientation selective units is similar to that of rabbit monocular visual cortex. The relative scarcity of orientation selective units and the absence of orientation columns differentiates rabbit from cat primary visual cortex. However, the majority of binocular units had similar receptive fields in each eye and very unconventional receptive fields were not encountered. Tested binocular units demonstrated summation upon simultaneous stimulation of both receptive fields. In conjunction with findings reported elsewhere, these results suggest that rabbit and cat possess a similar provision for binocular vision in spite of some differences in their cortical organisation.

Animals↗
PubMed1988

Imaging of cerebral blood flow and metabolism in amblyopia by positron emission tomography.

We used positron emission tomography to study monocular visual activation of various brain regions in four amblyopic and two normally sighted adults. Imaging of relative cerebral blood flow using the tracer H2(15)O showed reduced activation of primary visual cortex by the amblyopic as compared with the sound eye. Imaging of relative cerebral glucose metabolism using the tracer [18F]-2-deoxyglucose showed equal activation of primary visual cortex by either eye in the control subject, but reduced activation of primary and accessory visual cortex by the amblyopic as compared with the sound eye in two amblyopic subjects. Relative glucose metabolism was consistently higher in the frontal and temporal lobes contralateral to the viewing eye, both in normal and amblyopic subjects.

Amblyopia↗
PubMed1998

Vision for perception and vision for action in the primate brain.

Visual systems first evolved not to enable animals to see, but to provide distal sensory control of their movements. Vision as 'sight' is a relative newcomer to the evolutionary landscape, but its emergence has enabled animals to carry out complex cognitive operations on perceptual representations of the world. The two streams of visual processing that have been identified in the primate cerebral cortex are a reflection of these two functions of vision. The dorsal 'action' stream projecting from primary visual cortex to the posterior parietal cortex provides flexible control of more ancient subcortical visuomotor modules for the production of motor acts. The ventral 'perceptual' stream projecting from the primary visual cortex to the temporal lobe provides the rich and detailed representation of the world required for cognitive operations. Both streams process information about the structure of objects and about their spatial locations--and both are subject to the modulatory influences of attention. Each stream, however, uses visual information in different ways. Transformations carried out in the ventral stream permit the formation of perceptual representations that embody the enduring characteristics of objects and their relations; those carried out in the dorsal stream which utilize moment-to-moment information about objects within egocentric frames of reference, mediate the control of skilled actions. Both streams work together in the production of goal-directed behaviour.

Animals↗
PubMed2004

Neurotoxic lesion of anteromedial/posterior parietal cortex disrupts spatial maze memory in blind rats.

The primary visual cortex of rats is surrounded laterally (in Oc2L) and medially (in Oc2M) by several peristriate visual areas. Previous studies from our laboratory demonstrated that bilateral lesions in Oc2L result in visual pattern discrimination deficit, and in failure to solve a conditional discrimination which requires figure-background association. In contrast, neurotoxic lesions of the rostral part of Oc2M (which contains the anteromedial and anterior peristriate visual areas, collectively referred to as AM complex) result in deficits in visuospatial discrimination, and in disruptions in visual tasks involving spatial memory. The objective of this study was to behaviorally test the role of AM complex in a spatial memory task in absence of visual cues. For this purpose, we analyzed memory retention of Lashley III maze in blind rats after bilateral ibotenate lesions in AM complex, or in the primary visual cortex (V1, Oc1), to test the hypothesis that AM complex is essential for this cognitive task. The results showed a significant loss of memory retention of the maze in rats with lesions in AM complex, but not in rats with lesions in V1. Furthermore, the retention loss in rats with AM complex lesions was positively and significantly correlated with the size of the lesion. The results indicate a critical role of AM complex in spatial memory mechanisms independent on visual cues. A probable homology of rat AM complex with the posterior parietal cortex of primates is discussed.

Animals↗
PubMed2003

The growth of cat cerebral cortex in postnatal life: a magnetic resonance imaging study.

To follow up the development of an individual brain over time and to measure its growth we have analysed the brains of individual cats from postnatal day 12 to adulthood using magnetic resonance imaging. From the anatomical images, four parameters were calculated: anteroposterior extent of the telencephalon, brain volume, neocortical surface area and neocortical volume. The development of the anteroposterior extent was similar in all cats. It increased between the 3rd and 6th postnatal week from 33 to 37.5 mm ending up approximately 40 mm in adulthood. The brain volume showed greater variability. On average, the volume increased from 11.5 to 16.5 cm3 in the same period. Adult values were approximately 19 cm3. Considerable interindividual variability was observed in neocortical surface area. In one cat, it expanded from 12.5 to 26 cm2 between days 14 and 41. In another cat, this area expanded from 16 to 24.5 cm2 between days 12 and 40. On average, the surface area expanded by 34% between the 3rd and 6th week. Adult values ranged from 27 to 30 cm2. Neocortical volume increased from 2.9 to 4.1 cm3 between the 3rd and 6th postnatal week and to 4.5-5.2 cm3 in adulthood. The asymmetry between the hemispheres in both neocortical surface area and volume was < 3% in all animals for most of the observation period. Comparison of the neocortical surface measurements with data on postnatal growth of cat primary visual cortex obtained by 2-deoxyglucose autoradiography indicates that the primary visual cortex grows at the same speed and amounts to approximately 15% of the entire neocortical surface area throughout development.

Aging↗
PubMedDate not supplied

Shaping of receptive fields in the visual cortex during retinal maturation.

We present a computational study of the formation of simple-cell receptive field patterns in the primary visual cortex. Based on the observation that the spatial frequency of the retinal filter increases postnatally, our results explain differences in the time course of the development of orientation selectivity in binocularly deprived and normally reared kittens. Development after eye-opening in normal animals is modelled by training with natural images, whereas in the case of binocular deprivation noise-like stimulation continues. Further, it is shown that different orientation selectivities are obtained for network models trained with natural images in contrast to random phase images of identical second order statistics. The latter finding suggests that higher-order statistics of the inputs influences development of primary visual cortex. Finally, we search for quantities that identify possible signatures of natural image statistics in order to specify the amount of constructiveness that visual experience has on the formation of receptive fields.

Aging↗
PubMed1996

The role of anterior ectosylvian cortex in cross-modality orientation and approach behavior.

Physiological and behavioral studies in cat have shown that corticotectal influences play important roles in the information-processing capabilities of superior colliculus (SC) neurons. While corticotectal inputs from the anterior ectosylvian sulcus (AES) play a comparatively small role in the unimodal responses of SC neurons, they are particularly important in rendering these neurons capable of integrating information from different sensory modalities (e.g., visual and auditory). The present experiments examined the behavioral consequences of depriving SC neurons of AES inputs, and thereby compromising their ability to integrate visual and auditory information. Selective deactivation of a variety of other cortical areas (posterolateral lateral suprasylvian cortex, PLLS; primary auditory cortex, AI; or primary visual cortex, 17/18) served as controls. Cats were trained in a perimetry device to ignore a brief, low-intensity auditory stimulus but to orient toward and approach a nearthreshold visual stimulus (a light-emitting diode, LED) to obtain food. The LED was presented at different eccentricities either alone (unimodal) or combined with the auditory stimulus (multisensory). Subsequent deactivation of the AES, with focal injections of a local anesthetic, had no effect on responses to unimodal cues regardless of their location. However, it profoundly, though reversibly, altered orientation and approach to multisensory stimuli in contralateral space. The characteristic enhancement of these responses observed when an auditory cue was presented in spatial correspondence with the visual stimulus was significantly degraded. Similarly, the inhibitory effect of a spatially disparate auditory cue was significantly ameliorated. The observed effects were specific to AES deactivation, as similar effects were not obtained with deactivation of PLLS, AI or 17/18, or saline injections into the AES. These observations are consistent with postulates that specific cortical-midbrain interactions are essential for the synthesis of multisensory information in the SC, and for the orientation and localization behaviors that depend on this synthesis.

Anesthetics, Local↗
PubMed2004

Facilitation of visuo-motor learning by transcranial direct current stimulation of the motor and extrastriate visual areas in humans.

Performance of visuo-motor tasks requires the transfer of visual data to motor performance and depends highly on visual perception and cognitive processing, mainly during the learning phase. The primary aim of this study was to determine if the human middle temporal (MT)+/V5, an extrastriate visual area that is known to mediate motion processing, and the primary motor cortex are involved in learning of visuo-motor coordination tasks. To pursue this, we increased or decreased MT+/V5, primary contralateral motor (M1) and primary visual cortex excitability by 10 min of anodal or cathodal transcranial direct current stimulation in healthy human subjects during the learning phase of a visually guided tracking task. The percentage of correct tracking movements increased significantly in the early learning phase during anodal stimulation, but only when the left V5 or M1 was stimulated. Cathodal stimulation had no significant effect. Also, stimulation of the primary visual cortex was not effective for this kind of task. Our data suggest that the areas V5 and M1 are involved in the early phase of learning of visuo-motor coordination.

Adult↗
PubMed1991

Stereopsis in the cat: behavioral demonstration and underlying mechanisms.

The neural substrates subserving stereopsis were investigated behaviorally and electrophysiologically in the cat. In one set of studies, we examined behaviorally the ability of normal cats to perceive depth on the sole basis of spatial disparity using random-dot stereograms. Results showed that the animals were able to carry out this discrimination. We then evaluated the contribution of the optic chiasm, the corpus callosum and the primary visual cortex to this function. Results indicated that: (1) chiasma transection drastically reduced the ability of the animals to solve the random-dot problem; (2) a callosal split had little or no effect on their ability to relearn the same discrimination; (3) a section of both the corpus callosum and optic chiasm abolished this ability; and (4) bilateral lesions of areas 17-18 also abolished it. In another set of studies, we examined electrophysiologically the properties of neurons in the various visual cortical areas where disparity-based depth discrimination processes are presumed to take place. We recorded from areas 17, 18 and 19 of normal and split-chiasm cats. Results showed that: (1) the primary visual cortex of the normal cat contained cells sensitive to stimulus disparity; (2) these disparity sensitive neurons were also present in area 19 although in a much lower proportion and were more widely tuned than those in areas 17-18; and (3) following the section of the optic chiasm, there was a significant decrease in the number of disparity sensitive cells in areas 17-18, whereas in area 19 they were nearly completely absent. The results obtained from the lesion studies and from the single unit recording experiments indicate that stereoscopic depth perception is highly dependent in the cat upon the integrity of the through-the-chiasm geniculo-striate pathway and its target primary visual cortex.

Animals↗
PubMed2002

On the classification of simple and complex cells.

In their pioneering studies of primary visual cortex, Hubel and Wiesel described the existence of two classes of cells, which they termed "simple" and "complex". The original classification scheme was based on a number of partly subjective tests of linear spatial summation. Later, investigators adopted an objective classification method based on the ratio between the amplitude of the first harmonic of the response and the mean spike rate (or the F(1)/F(0) ratio) when the neuron is stimulated with drifting sinusoidal gratings. This measure is bimodally distributed over the population and divides neurons into two classes that correspond closely to the classical definition by Hubel and Wiesel. Here we show that a simple rectification model can predict the observed bimodal distribution of F(1)/F(0) in primary visual cortex when the distributions of the intracellular response modulation and mean are unimodal. Thus, contrary to common belief, the bimodality of F(1)/F(0) does not necessarily imply the existence of two discrete cell classes. Furthermore, in reviewing the literature, we find no independent support for a simple/complex dichotomy. These results suggest that the existence of two distinct neural populations in primary visual cortex, and the associated hierarchical model of receptive field organization, need to be re-evaluated.

Electrophysiology↗
PubMed2004

Ocular dominance column width and contrast sensitivity in monkeys reared with strabismus or anisometropia.

PURPOSE: To study the relationship between the width of ocular dominance columns in primary visual cortex and spatial contrast sensitivity functions in monkeys with strabismus or anisometropia during infancy. METHODS: Adult monkeys having had monocular visual abnormalities induced in infancy were tested behaviorally for spatial contrast sensitivity and then subjected to functional enucleation of one eye to reveal the ocular dominance columns (ODCs) of the primary visual cortex by cytochrome oxidase (CO) staining. The relative widths of the left and right eyes' ODCs were measured and related to the contrast sensitivity functions. RESULTS: The relative widths of the ODCs having input from eyes with strabismic or anisometropic amblyopia were reduced in proportion to the age of onset and the duration of the early visual abnormality. The relative losses in contrast sensitivity were in ordinal agreement with the losses in relative width of the ODCs. CONCLUSIONS: Amblyopia induced by the early monocular abnormalities of strabismus or anisometropia is proportional to the loss in cortical afference as reflected in the reduction in width of the respective ODCs in the primary visual cortex.

Amblyopia↗
PubMed1982

Facilitatory effects of intermittent photic stimulation on visual cortical kindling.

There are few reports on kindling preparation by daily electrical stimulation to the primary visual cortex. In our previous studies on cats, it was demonstrated that repeated stimulation to the primary visual cortex brought a similar progress in seizure development as in amygdaloid kindling, although it took more trials. In this study, we examined the effects of intermittent photic stimulation (IPS) (2.5 Hz) on the visual cortical kindling preparation to clarify more underlying mechanisms of photosensitivity. Under IPS, afterdischarges synchronizing to IPS were seen and a duration of afterdischarge was extremely prolonged, even in the early stage of the kindling process. The threshold of stimulus intensity inducing afterdischarge was significantly reduced and the generalized convulsive seizure was obtained with fewer times of stimulation, as compared to visual cortical kindling without IPS. In visual cortical kindling myoclonic responses were sometimes caused by IPS for a few minutes immediately after cessation of the electrically induced generalized seizure. Such phenomena were never seen in amygdaloid kindling. These results indicate that IPS facilitates a seizure development in all stages of visual cortical kindling.

Animals↗
PubMedDate not supplied

Reaching out to see: arm position can attenuate human visual loss.

Electrophysiological recordings in monkeys have now revealed several brain regions that contain bimodal visuotactile neurons capable of responding to either tactile or visual stimuli placed on or near the hands, arms, and face. These cells have now been found in frontal, parietal, and subcortical areas of the monkey brain, suggesting a cortical network of neurons that preferentially represent near peripersonal space. The degree to which the visual responses of such cells rely on input from the primary visual cortex and the extent to which they may contribute to visual perception is not completely understood. Nonetheless, recent neuropsychological studies suggest that a similar representation of near space may be bimodally coded in humans as well. Given the accumulating evidence for specialized processing of visual stimuli placed near the hands and arms, we hypothesized that arm position may be capable of modulating human visual ability. Here we report the case of WM, who lost his ability to see in his left visual hemifield after sustaining damage to his right primary visual cortex. Interestingly, the placement of WM's left arm into his "blind" field resulted in significantly better detection of left visual field stimuli compared to when his hand was placed in his lap at midline. Moreover, we found this attenuation to be confined to stimuli presented within reaching distance (unless a tool that extended WM's reach was held while he performed the test). These findings are highly consistent with the characteristics of the bimodal visuo-tactile neurons that have been described in monkeys. Thus, it seems that arm position can modulate human visual ability, even after damage to the primary visual cortex. This study provides an exciting bridge between monkey neurophysiology and human visual capacity while also offering a novel approach for improving visual defects acquired via cortical injury.

Aged↗
PubMed1989

Identification and localization of 5-hydroxytryptamine receptor sites in macaque visual cortex.

The two main receptor subtypes for 5-hydroxytryptamine (5HT) were measured and localized in visual cortical areas of macaque monkey. [3H]5HT was used to label all 5HT-1 receptor subtypes and [3H]ketanserin was used to label 5HT-2 receptors. Both receptor types could be demonstrated in membranes prepared from macaque primary visual cortex. The specificity of these ligands for 5HT-1 or 5HT-2 receptors was demonstrated by the pharmacological profile of inhibitors of the specific binding. 5HT-1A receptor sites were detected by displacement experiments and by direct labeling with [3H]8-hydroxy-2(di-n-propylamino) tetralin 8OH-DPAT. Receptor autoradiography showed that the distribution of these receptor subtypes varied from one part of visual cortex to another. 5HT-1 receptors, labeled with [3H]5HT were present in several bands through layer IV of primary visual cortex with the densest band seen in and above layer IVA: another band was in lower layer VI. The band in layer VI was predominantly 5HT-1A sites. There were two main bands of 5HT-2 receptor sites, the most prominent around the IV/V boundary, and the other extending from layer IVA upwards. Adjacent areas showed 5HT receptors in a broad band corresponding to layer IV. 5HT-1A sites were found in superficial layers of adjacent areas, except V2. These layering patterns did not correspond precisely with cytoarchitectonic layering, nor with the pattern of 5HT-containing presynaptic fibres in published reports. It is important, therefore, in considering the role of the 5HT-containing neurons in cortical function to take account not only of the anatomy of the presynaptic terminals, but also of the postsynaptic receptors upon which the released transmitter will act, and their location within the cortex.

8-Hydroxy-2-(di-n-propylamino)tetralin↗