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S LeVay

Publications and source records attributed to S LeVay.

36 records · Page 2Linked to original sources
PubMed1981

Visual claustrum: topography and receptive field properties in the cat.

A region containing visually responsive cells was found in the dorsocaudal claustrum. This area contains a single orderly map of the contralateral visual field. Like cortical cells, most claustral cells are selective for stimulus orientation. They are binocular, and they respond to either direction of movement and to a broad range of velocities. Their most striking property is a marked preference for very long stimuli.

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PubMed1981

The visual claustrum of the cat. I. Structure and connections.

The cat's dorsocaudal claustrum was studied in Golgi preparations, by electron microscopy, and by anterograde and retrograde tracer techniques. It receives a convergent retinotopic projection from several visual cortical ares, including areas 17, 18, 19, 21a and PMLS (posteromedial lateral suprasylvian area). The projection arises from spiny dendrite cells (pyramidal and fusiform) in the middle of cortical layer VI. As shown by a double label experiment, they form a separate population from those projecting to the lateral geniculate nucleus. There are also inputs from the lateral hypothalamus, from the nucleus centralis thalami, and probably from the locus coeruleus, but not from the sensory nuclei of the thalamus. Non-visual cortical areas do not project to the visual claustrum, but many of them are connected to other parts of the nucleus. For example, the splenial (cingulate) gyrus projects to a claustral zone just ventral to the visual area, and regions anterior to the visual area are connected with somatosensory and auditory cortex. The commonest cell type in the claustrum is a large spiny dendrite neuron whose axon leaves the nucleus after giving off local collaterals. Small spine-free cells, with beaded dendrites and a locally arborizing axon, are found also. Electron microscopy of the claustrum after ablation of the visual cortex showed degenerating type 1 axon terminals synapsing on spines and beaded dendrites, suggesting a direct cortical input to both cell types. The visual claustrum projects back to the visual cortex, to the same areas from which it receives an input. The return projection is predominantly ipsilateral, but there is, in addition, a small crossed projection. The claustrocortical axons terminate in all cortical layers but most heavily in layers IV and VI. The majority of the cells in the visual claustrum project to the cortex, and retinotopy is maintained throughout the entire corticoclaustral loop. No subcortical projections from the claustrum could be identified.

Afferent Pathways↗
PubMed1981

The visual claustrum of the cat. II. The visual field map.

Physiological and anatomical methods were used to study the representation of the visual field in the cat's dorsocaudal claustrum. In one set of experiments, the visual receptive fields of claustral neurons were plotted in multiple electrode penetrations. In another set of experiments, the termination of the corticoclaustral pathway was examined autoradiographically after the injection of [3H]proline at retinotopically defined sites in the visual cortex. Results obtained by the two methods were in close agreement. The claustrum was found to contain a single, orderly map of the contralateral hemifield and a small part of the ipsilateral field. High elevations are represented caudally and ventrally, low elevations rostrally and dorsally. The surface of the claustrum represents the periphery of the visual field, while the vertical meridian lies more ventrally, where the visual claustrum abuts the non-visual part of the nucleus. Visual field lines (isoazimuths or isoelevations) are represented as planes in the claustrum. The map is unusual in that isoazimuth planes are strongly curved and nested within each other, with peripheral ones enclosing those closer to the vertical meridian. This arrangement permits an expanded representation of the periphery compared with what is seen in visual cortex. The inputs from areas 17, 18, 19, 21a, and PMLS (posteromedial lateral suprasylvian area) are convergent, each projection retinotopically to the entirety of the claustral map.

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PubMed1981

The visual claustrum of the cat. III. Receptive field properties.

The visual response properties of cells in the cat's dorsocaudal claustrum were studied physiologically. Quantitative observations were made of 55 cells, and qualitative observations were made on 228 others. The claustral cells formed a physiologically homogeneous population. The overwhelming majority were orientation selective, and most also showed a striking preference for long stimuli, their responses summating up to lengths of 40 degrees or more. Moving stimuli were always much more effective than stationary ones. In other respects, claustral cells were tolerant of wide variation in stimulus features. Their responses were about equally brisk to either direction of movement of a properly oriented stimulus, and the velocity of movement was likewise not critical. They appeared not to summate across the dimension of their receptive fields orthogonal to the preferred orientation so that narrow or broad slits, or edges, evoked similar responses. Dark slits on light backgrounds were as effective as light slits on dark backgrounds. Finally, a large majority of cells were driven equally well by either eye. These properties of claustral cells differ in several respects from those of their principal targets, cells in layer IV of visual cortex.

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PubMed1979

Siamese cat: altered connections of visual cortex.

In siamese cats, each side of the brain receives a retinal input serving part of the ipsilateral visual field as well as the normal contralateral field representation. Both corticothalamic and cortico-cortical projections are systematically rearranged, but while one is retinotopically appropriate, the other fails to make a distinction between ipsilateral and contralateral fields. Different rules appear to govern the development of these two sets of connections.

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PubMed1977

Relay cell classes in the lateral geniculate nucleus of the cat and the effects of visual deprivation.

This study presents evidence that the X- and Y-cells described physiologically in the A laminae of the cat's dorsal lateral geniculate nucleus (LGN) are two morphologically distinct cell types recognizable in Golgi preparations. It is shown firstly that the three cell types seen in Golgi preparations of the A laminae (large and medium-sized principal cells and small interneurons-types 1,2 and 3 in the classification of Guillery, '66) may be identified in 1-mum Epon sections of osmicated material. While cell-diameter histograms prepared from serial 1-mum sections show a unimodal distribution of cell sizes, three populations can be distinguished if attention is paid to the presence or absence of large cytoplasmic inclusions (laminar bodies). These three populations consist of large cells lacking laminar bodies (Class I), medium-sized cells possessing laminar bodies (Class II) and small cells lacking them (Class III). That these three classes correspond to the three morphological types has been shown by (i) size comparisons, and (ii) direct demonstration of laminar bodies in the Golgi-impregnated cell bodies of Guillery's type 2 cells. Histograms prepared in this way for samples taken at various positions in the LGN show that the numbers of class II cells decline from the representation of the area centralis to the monocular segment. This decline is compensated by a corresponding rise in the numbers of class I cells. This pattern of distribution is similar to the physiologically observed distribution of X- and Y-cells, indicating that X-cells are likely to be class II cells and Y-cells class I cells. The cortical projections of the various cell types have been examined by the horseradish peroxidase method. Class II cells project to area 17 only. Most class I cells also project to area 17 only, but a few very large class I cells project to area 18. From our results, it appears that very few if any cells in the A laminae have branching axons supplying both 17 and 18. The class III cells do not project to the visual cortex, a finding consistent with their identification as interneurons. Class I and II cells are also found in lamina C and in the MIN. In both these regions there is a predominance of very large class I cells, which project to area 18. Laminae Cl-C3 contain small cells lacking laminar bodies. These cells may project to both areas 17 and 18 with branching axons. They are likely to correspond to Guillery's type 4 cells (small relay cells confined to the C laminae) and to the physiologically described W-cells. Long-term monocular deprivation causes cell shrinkage which is much more severe for class I than for class II cells. There is in addition a decrease in the relative numbers of class I cells. This decrease is found in binocular deprivation also. These observations provide an anatomical basis for the reported loss of Y-cells from deprived laminae of the LGN. It is suggested that the effects of deprivation on Y-cells may be accounted for in terms of competition for synaptic space.

Animals↗
PubMed1977

Effects of visual deprivation on polyribosome aggregation in visual cortex of the cat.

Neurons in the visual cortex of 48 normal and visually deprived kittens and cats were examined electron microscopically for the presence of absence of polyribosomes in their perikaryal cytoplasm. In normal animals at most ages the ribosomes of cortical neurons were aggregated into polysomes, but during the second and third months of life -- a period corresponding approximately to the physiologically defined critical period -- variable numbers of cells were found which contained ribosomes only in the monomeric form. The affected cells were spiny stellate neurons in the fourth layer of the cortex. Even within the critical period, however, cells with dispersed ribosomes were not found in every animal examined.

Animals↗
PubMed1976

Laminar patterns of geniculocortical projection in the cat.

The cortical afferents from individual laminae of the dorsal lateral geniculate nucleus (LGN) were studied using both light and electron microscope autoradiography. In area 17, the A geniculate laminae (A and A1) had two main bands of projection, one extending from the bottom of IVc to the deepest cells in layer III, and one in layer VI. The C geniculate laminae projected in two dense bands to the upper and lower borders of layer IV, thus bracketing the A laminae projection, though with some overlap. In addition, the C laminae projected to the superficial half of layer I, which the A laminae did not. Conversely, while the A laminae projected to layer VI, the C laminae did not. The two sets of laminae also showed differences in the areas to which they projected. The A geniculate laminae projected to areas 17 and 18, whereas the C geniculate laminae had a more extensive projection, including areas 17, 18, 19 and other areas on the suprasylvian gyrus. The laminar organization of the projection to area 18 was similar to that found in area 17. At the electron microscopic level the geniculate terminals were found to make Gray's type 1 synapses, for the most part onto dendritic spines. Labeled terminals were found in all the projection bands seen in the light microscope. The implications of these findings on the connectivity of cells in layer IV are discussed. The presence of labeled terminals in layer VI, which contains the cells of origin of the corticogeniculate pathway, suggests that the recurrent loop to the LGN is mediated monosynaptically. Finally, the afferents from each geniculate lamina were found to be segregated into patches, about 500 mum wide, which probably form the anatomical basis for ocular dominance columns.

Animals↗
PubMed1975

Mode of termination of retinotectal fibers in macaque monkey: an autoradiographic study.

The distribution of retinotectal projections was studied in 4 macaque monkeys by examining the tectum autoradiographically 3-21 days after eye injection with radioactive proline or a proline-fucose mixture. Contrary to previous reports the optic fibers project to all regions of the tectum including a relatively sparse but nevertheless very clear projection to the anterolateral one-third, where the fovea is represented. Here the terminals were distributed within the superficial grey layer of the tectum at a depth extending from about 50 mum to 125 mum and in a patchy fashion, with a tendency to aggregation in clumps 0.1-0.5 mm wide from one or other eye. Further posteromedially, corresponding to more peripheral retinal regions, the input from the contralateral eye became more continuous superficially, with tongues extending more deeply in the superficial grey, apparently enclosing clumps of ipsilateral terminals. These deeper ipsilateral clumps occupied a rather well defined layer extending in depth from about 100 mum to about 175 mum. Still further posteromedially, in the temporal crescent representation, only the continuously distributed label from the contralateral eye was found. Continuous label was also seen in the optic disc region on the ipsilateral side; on the corresponding area contralaterally, label was absent. Both ipsilaterally and contralaterally, the pattern of input was roughly symmetrical about the representation of the horizontal meridian, which ran from anterolateral to posteromedial. The regional aggregations of input from one or other eye were to some extent reflected physiologically in a regional variation in eye dominance, though this was perhaps less than might have been expected from the marked heterogeneity of the inputs.

Afferent Pathways↗
PubMed1975

The pattern of ocular dominance columns in macaque visual cortex revealed by a reduced silver stain.

A pattern of alternating dark and pale bands was observed in the striate cortex of the macaque monkey. The bands, which ran parallel to the surface, were seen in tangential sections stained with a reduced silver method for normal fibers and were most clear in layer 4C alpha, immediately deep to the line of Gennari. The dark bands were about 300 mu wide and showed blind endings and bifurcations. The light bands were about 50 mu wide and did not branch or terminate within area 17. Because the dark bands were similar in width to the bands of terminal degeneration which have been shown to result from single-layer lesions of the lateral geniculate body, it seemed possible that they corresponded to ocular dominance columns. To test this idea, the boundaries of ocular dominance columns were marked in a physiological experiment: tangential electrode penetrations were made in an anesthetized monkey and, as the electrode was advanced horizontally in the fourth layer, the eye preference of single units and of the background activity was monitored. Small electrolytic lesions were placed at the points where a change in eye preference occurred. The brain was subsequently fixed, sectioned tangentially and stained with the silver method. All the lesions--total of 12 --fell directly on the pale bands. Moreover, the electrode had not passed over any pale bands without a lesion being placed. It was concluded that the dark bands do correspond to single ocular dominance columns and the pale bands to the boundaries between columns. The banding appearance is due to a greater density of tangential fibers within columns than at the borders of columns. These tangential fibers are in part the preterminal arborizations of geniculocortical axons, since some of them have been shown to degenerate after geniculate lesions. The ocular dominance columns were mapped for most of the striate cortex, using serial tangential sections stained with the silver method. The overall pattern was ,imilar in several monkeys, though the details of the branching arrangements varied from animal to animal. The columns met the 17-18 border at right angles. On the outer surface of the hemisphere the columns converged from the 17-18 border, turned medially with repeated fusions of columns, and streamed over the lip of the calcarine fissure. In the roof of the fissure they met a second system of columns oriented parasagittally. In terms of the visual field, the columns ran roughly horizontally for the central 10 degrees of the field, and circumferentially beyond that. The columns were not mapped in the stem of the fissure, the area corresponding to the far periphery of the field. The constancy of column width across the cortex probably allows a functional matching between ocular-dominance and orientation columns.

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