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PubMed1989

Functional consequences of modification of callosal connections by perinatal enucleation in rat visual cortex.

The effects of neonatal monocular enucleation (right eye) on the callosal connections in the rat visual cortex were studied by physiological and morphological methods. Evoked activity was recorded in the left hemisphere, i.e. contralaterally to the enucleated eye. After enucleation, trans-callosally evoked responses were recorded in a widened stripe of the lateral visual cortex. Compared with the controls, the responsive area was expanded laterally and medially, i.e. into the lateral part of the primary visual area and within the secondary visual cortex (lateral part). Within about 0.5 mm of the expansion, the responses did not differ from those recorded in areas with "normal" callosal connections. Morphological evidence is presented suggesting that this expansion of evoked responses with high amplitudes and short latencies corresponds to an extension of callosal connections with a high density of axon terminals in layers two and three. Further medially within the primary visual cortex, callosally evoked responses with low amplitudes and longer latencies were recorded. The main types of unit responses and characteristic interactions between visually and callosally evoked responses are shown and discussed. These results suggest that following neonatal enucleation (1) the callosal connections expand and form functional synapses in the lateral part of the visual cortex, (2) these connections can activate cortical neurons either directly or by mediation of associational connections between the lateral secondary and primary visual cortex areas and (3) callosal connections can interact with visually evoked potentials and unit responses.

Animals↗
PubMed1985

Localization of glutaminase-like and aspartate aminotransferase-like immunoreactivity in neurons of cerebral neocortex.

The distribution of glutaminase (GLNase)- and aspartate aminotransferase (AATase)-immunoreactive cells was examined in the cerebral neocortex of rat and guinea pig and in the somatic sensorimotor and primary visual cortex of the Macaca fascicularis monkey. These enzymes are involved in the metabolism of glutamate and aspartate, two amino acids thought to be excitatory amino acid transmitters for cortical neurons. In each of the species examined a large percentage of layer V and VI pyramidal neurons have pronounced glutaminase-like immunoreactivity (GLNase IR). In contrast, neurons in layers I, II, and IV show little GLNase IR. Layer III in the rat and guinea pig contains only a few, densely labeled GLNase-like-immunoreactive (GLNase-Ir) pyramidal neurons, whereas in the monkey the number of GLNase-Ir cells in layer III varies between cytoarchitectonic fields. Area 3b of the primary somatic sensory cortex and area 17 (primary visual cortex) contain few GLNase-Ir cells in layer III. However, layer III contains moderate numbers of GLNase IR in cells in areas 3a, 1, 2, 5, and in the primary motor cortex. Within the motor cortex the largest pyramidal ("Betz") cells are not labeled. In marked contrast to the results with antibody to GLNase, antibody to AATase labels cells that appear nonpyramidal in form, and these cells are in all cortical layers in each of the species examined. This distribution is roughly similar throughout all areas of rodent neocortex, but in monkey visual cortex AATase-immunoreactive neurons are more numerous in layers II-III, IVc, and VI. When combined with the findings of other studies, our results suggest that GLNase IR marks pyramidal neurons that use an excitatory amino acid transmitter. Antibody to AATase appears to mark intrinsic cortical neurons. The AATase immunoreactivity of these cells could indicate that they use an excitatory amino acid transmitter. However, their form and distribution in cortex suggest that this antibody labels GABAergic neurons.

Animals↗
PubMed1988

The effects of ablation of visual cortex in neonatal rabbits on the organization of retinothalamic and retinopretectal projections.

Primary visual cortex was ablated unilaterally in neonatal rabbits. Following a survival of 2-4 months, retrograde degeneration of the dorsal lateral geniculate nucleus (LGd) was assessed, and reorganization of retinofugal pathways was studied using methods of anretrograde transport of [3H]proline or of horseradish peroxidase. A complete lesion of primary visual cortex resulted in complete retrograde degeneration of the LGd with no sparing of any class of neurons. The terminations of retinofugal axons in the pretectum and thalamus were compared with those observed in normal animals. No major reorganization of ipsilateral retinofugal projections was observed in either the thalamus and pretectum ipsilateral to the ablated cortex, or in the thalamus and pretectum contralateral to the ablated cortex. However, contralateral retinofugal projections to the thalamus and to the pretectum ipsilateral to the ablated cortex were significantly different from normal. In the thalamus, the projections to the lateral posterior nucleus were expanded in area and increased in density. In the pretectum, the projections to the rostral pretectal areas were greatly increased in area, especially in the region of the olivary pretectal nucleus and posterior pretectal nucleus. However, the density of these projections was not increased relative to normal. Consideration of these results in relation to other published data on the anatomical consequences of neonatal visual cortex lesions, both in mammals which show behavioral sparing following neonatal visual cortex lesions and in mammals which, like the rabbit, show no behavioral sparing, suggests that: (1) behavioral sparing may correlate with patterns of survival or death of neurons in the thalamus and retina; and (2) reorganization of retinofugal pathways is not necessarily associated with behavioral sparing.

Animals↗
PubMed1989

Intraocular injections of tetrodotoxin reduce transiently expressed acetylcholinesterase activity in developing rat visual cortex.

Geniculo-recipient layers of primary visual cortex in the rat display a transient pattern of acetylcholinesterase (AChE) activity during the second postnatal week of life. Previous work has demonstrated that neonatal enucleations markedly reduce the transient AChE activity in visual cortex. The present studies were undertaken to determine the effects of reduced afferent neural activity on expression of the transient pattern of AChE activity. Rat pups received intraocular injections of tetrodotoxin (TTX) on postnatal days (PND) 3, 5, 7, 9 and 11 and were sacrificed on PND 12. Some animals were enucleated on PND 3. Brain sections were processed for AChE histochemistry and analyzed by optical densitometry. These experiments show that uniocular injections result in a markedly decreased level of AChE activity in layer IV of the medial part of cortical area 17 contralateral to the injected eye. The degree of reduction of AChE activity from repeated TTX injections was similar to the degree of reduction following enucleation on PND 3. Binocular injections of TTX result in a reduction of AChE activity in layer IV throughout cortical area 17, similar to the effects of binocular enucleation on PND 3. Experiments combining injection of horseradish peroxidase along with TTX on PND 11 demonstrate that retinal ganglion cells of TTX injected eyes are still capable of anterograde axonal transport. These data demonstrate that normal innervation and afferent activity are necessary for the transient expression of AChE activity by geniculocortical neurons.

Acetylcholinesterase↗
PubMed1990

Lateral interactions in visual cortex.

The findings presented in these studies have brought out different ideas concerning the mechanisms of processing in primary visual cortex than were held at the outset. Rather than thinking of receptive fields as being restricted in their extent, with the process of integration of the components of an image occurring at a much later stage along the visual pathway, we have shown that the integrative process is a progressive one, beginning in the primary visual cortex (or perhaps even earlier) and building up in a cascading series of converging and diverging connections. Rather than thinking of the filter characteristics of a cell as being fixed, it is apparent that they are dynamic and can be modified by the context in which features are presented. Finally, rather than a cortex with a functional architecture that is fixed after a critical period ending in infancy, we find that perturbing the system can lead to long-term topographical reorganization. Other examples of contextual interactions have been demonstrated in the submodalities of motion, where a cell's directional selectivity is modulated by the presence of movement in the surround (Allman et al. 1985; Tanaka et al. 1986; Gulyas et al. 1987; Orban et al. 1987). In the domain of color, the phenomenon of color constancy, reported for cells in visual area V4 (Zeki 1983), also requires lateral interactions in visual space, comparing the wavelength distribution of light coming from surfaces in different parts of the visual field. The influences presented in these studies, as in our own work in the domain of orientation, are modulatory. The long-term changes in cortical topography following removal of somatosensory input (Merzenich et al. 1984, 1988) or by retinal lesions suggest that with the appropriate manipulations the lateral interactions can be enhanced to the point of activating the postsynaptic cells. Although retinal lesions clearly represent an abnormal disruption of sensory input, they may nevertheless be representative of long-term reorganizations of neural networks occurring under normal circumstances, such as those required for memory.

Animals↗
PubMed1977

[Types of receptive fields of neurons in different laminae of the rabbit visual cortex].

Neurons of the primary rabbit visual cortex were classified into 7 large groups according to features of their receptive fields. The neurons with receptive fields were mostly revealed in the layers IV and VI, those with uniform directional receptive fields--in layer V, those with simple I-in layer VI, those with simple II--in layer II + III, and those with hypercomplex--in layer IV. The neurons with concentric receptive fields and those without responses to visual stimuli were equally distributed over the layers. The data obtained in rabbits, cats, and monkeys suggest that the tendency towards function stratification of primary visual cortex is successive in an evolutionary order of mammals.

Animals↗
PubMed1990

Quantitative analysis of a vulnerable subset of pyramidal neurons in Alzheimer's disease: II. Primary and secondary visual cortex.

In this study we investigated the primary and secondary visual areas of normal and Alzheimer's disease brains by using the SMI32 antibody. It is known that in Alzheimer's disease primary sensory areas are usually less devastated than association cortices, although visual symptomatology has been documented early in the course of the disease. In area 17, the SMI32 antibody primarily labeled the perikarya and dentritic tree of the large Meynert cells and cells in layer IVB. Smaller neurons in layers III, V, and VI were also immunoreactive (ir). In area 18, very large SMI32-ir pyramidal neurons in layers III and V were observed. In both areas, staining intensity was correlated with cell size, the largest neurons being the most intensely stained. Only a few changes were observed in the Alzheimer's disease cases. The only statistically significant differences in SMI32-ir neuron counts between control and Alzheimer's disease brains occurred in layer IVB cells and Meynert cells in area 17, and in layer III cells in area 18. In contrast with association cortices, there were no changes in staining intensity in the visual areas. There were fewer neurofibrillary tangles and neuritic plaques in these areas than in prefrontal and inferior temporal cortex, and a correlation between neurofibrillary tangle counts and SMI32-ir neuron loss was only observed in layer III of area 18. These observations show that in the primary and secondary visual cortex, SMI32 also labeled a distinct subset of pyramidal cells that are known from data obtained in the monkey brain to furnish long corticocortical as well as subcortical projections. Interestingly, although there is much less cell and/or neurofibrillary tangle formation in these occipital regions than in prefrontal and temporal association areas, there is significant loss within key subsets of pyramidal cells. The selective loss of this particular subpopulation of pyramidal neurons will disrupt association pathways linking primary visual cortex with areas involved in higher level visual processing. The partial disconnection of such pathways may be relevant to the visual symptomatology frequently observed in Alzheimer's disease patients. These data further support the hypothesis that subtypes of pyramidal neurons with specific anatomical and molecular profiles may display a differential vulnerability in Alzheimer's disease.

Aged↗
PubMed1988

Coherent oscillations: a mechanism of feature linking in the visual cortex? Multiple electrode and correlation analyses in the cat.

Primary visual coding can be characterized by the receptive field (RF) properties of single neurons. Subject of this paper is our search for a global, second coding step beyond the RF-concept that links related features in a visual scene. In recent models of visual coding, oscillatory activities have been proposed to constitute such linking signals. We tested the neurophysiological relevance of this hypothesis for the visual system. Single and multiple spikes as well as local field potentials were recorded simultaneously from several locations in the primary visual cortex (A17 and A18) using 7 or 19 individually advanceable fiber-microelectrodes (250 or 330 microns apart). Stimulus-evoked (SE)-resonances of 35-85 Hz were found in these three types of signals throughout the visual cortex when the primary coding channels were activated by their specific stimuli. Stimulus position, orientation, movement direction and velocity, ocularity and stationary flicker caused specific SE-resonances. Coherent SE-resonances were found at distant cortical positions when at least one of the primary coding properties was similar. Coherence was found 1) within a vertical cortex column, 2) between neighbouring hypercolumns, and 3) between two different cortical areas. We assume that the coherence of SE-resonances is mediated by recurrent excitatory intra- and inter-areal connections via phase locking between assemblies that represent the linking features of the actual visual scene. Visually related activities are, thus, transiently labelled by a temporal code that signalizes their momentary association.

Action Potentials↗
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↗
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↗
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↗
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↗
PubMed1990

A model for the estimate of local image velocity by cells in the visual cortex.

Some computational theories of motion perception assume that the first stage en route to this perception is the local estimate of image velocity. However, this assumption is not supported by data from the primary visual cortex. Its motion sensitive cells are not selective to velocity, but rather are directionally selective and tuned to spatio-temporal frequencies. Accordingly, physiologically based theories start with filters selective to oriented spatio-temporal frequencies. This paper shows that computational and physiological theories do not necessarily conflict, because such filters may, as a population, compute velocity locally. To prove this point, we show how to combine the outputs of a class of frequency tuned filters to detect local image velocity. Furthermore, we show that the combination of filters may simulate 'Pattern' cells in the middle temporal area (MT), whereas each filter simulates primary visual cortex cells. These simulations include three properties of the primary cortex. First, the spatio-temporal frequency tuning curves of the individual filters display approximate space-time separability. Secondly, their direction-of-motion tuning curves depend on the distribution of orientations of the components of the Fourier decomposition and speed of the stimulus. Thirdly, the filters show facilitation and suppression for responses to apparent motions in the preferred and null directions, respectively. It is suggested that the MT's role is not to solve the aperture problem, but to estimate velocities from primary cortex information. The spatial integration that accounts for motion coherence may be postponed to a later cortical stage.

Animals↗
PubMedDate not supplied

[Relationship between level of vigilance and changes in the receptive fields of the cat visual cortex].

The activity of 118 neurones of the primary visual cortex (17th field) was studied in unanesthetized cats, immobilized with d-tubocurarine, in a state of calm wakefulness and in strained attention, alarm. The strained attention was elicited by an air-puff directed to the corner of the closed eye, not used for the photic stimulation. Considerable rearrangments of the receptive field of neurones (94%) were observed in the state of strained attention. In the majority of the studied cortical cells (75%) during 10-30 minutes the excitatory centres of their receptive fields became narrower while their inhibitory periphery widened; in the cells with the inhibitory centres of the receptive fields they were larger in 80% of the cases. It is shown that with dark, mesopic and scotopic adaptation the major characteristics of the changes in the receptive fields remain unaltered. It is assumed that these effects have a behavioural value for the organism, because the created rise in the level of alertness is accompanied by a sharpening of the receptive fields, i.e. by a greater ability to a fine analysis and recognition of visual images.

Adaptation, Physiological↗
PubMed1992

[Examination of the visual system with transcranial magnetic stimulation].

The influence of transcranially applied magnetic stimuli on the function of the afferent (sensory) and efferent (motor) parts of the visual system have been discussed. Excitatory (positive) phenomena are subjective photic sensations (phosphenes) which can be elicited by transcranial magnetic stimulation over occipital parts of the skull. The phosphenes appear on the left or right side of the visual field depending upon the direction of the coil currents, which determines whether the visual cortex of the right or the left hemisphere is activated. The configuration of the phosphene fields hints at an excitation of the primary visual cortex (Brodmann's area 17). However, magnetic brain stimulation also produces inhibitory (negative) phenomena. When strong magnetic field pulses are applied over the primary visual cortex, foveally presented visual stimuli cannot be identified even when no phosphenes are perceived at the same time. Depending on the position of the stimulation coil, this suppression of perception can be restricted to visual stimuli presented on the right, or left of, above or below the fixation point. No generation or disturbance of eye movements by transcranial magnetic stimulation has been reported before, except for a delay of saccades within a reaction time paradigm.

Animals↗
PubMed1994

Neocortical grafts receive functional afferents from the same neurons of the thalamus which have innervated the visual cortex replaced by the graft in adult rats.

Electrophysiological and anatomical studies were carried out in parallel to investigate the ability of lateral geniculate body neurons to regenerate axons damaged by the removal of the primary visual cortex and to innervate graft neurons functionally after transplantation of fetal neocortical tissue to a lesion cavity in the brain of adult rats. In electrophysiological experiments neurons of a large portion of the transplants (14/35) displayed visual responses with characteristics resembling closely those of normal primary visual cortex; these transplants also displayed a different degree of restoration of topographically organized visual field representations on them. To demonstrate anatomical regeneration of inputs from the host lateral geniculate body to the graft, injections of FluoroGold were made before grafting into the intact visual cortex for retrograde labeling of the lateral geniculate body neurons. After completion of the microelectrode recordings from the transplants a second dye, Bisbenzimide, was injected into the transplants. The rats with transplants whose neurons displayed responses to visual stimulations contained in the lateral geniculate body neurons with FluoroGold-labeled cytoplasm and Bisbenzimide-labeled nuclei. The presence of double-labeled neurons suggests that the same neurons, the axons of which have terminated in area 17 of the cortex, innervated the transplants functionally through the regeneration of damaged axons.

Animals↗
PubMed1995

Scotoma perception in white-noise-field campimetry and postchiasmal visual pathway lesions.

The authors examined 59 patients (32 women and 27 men) suffering from homonymous hemianopia by white-noise-field campimetry (Tübingen Electronic Campimeter) and by conventional perimetry (Tübingen Automatic Perimeter or Tübingen Manual Perimeter) and by computerized tomography (CT) or magnetic resonance imaging (MR). In all, 56 patients showed neuroradiologically detectable cerebral lesions, which were superimposed in a reconstructed "reference brain". Of these 56 patients, 18 were not capable of perceiving any white-noise-field scotoma, although their conventional perimetric findings showed defects. Lesions of these patients were concentrated along the optic radiation and spared the primary visual cortex. The lesions of the remaining 38 patients with scotoma detectable in both methods were accumulated in area V1, the primary visual cortex. The lesions of 6 patients, who had had persistent scotoma perception for more than 2 years, were situated at the occipital pole. The lesions of 8 patients with vanishing scotoma were concentrated in more rostral areas.

Adolescent↗