Showing papers on "Orientation column published in 1971"

Visual field projection columns and magnification factors in the lateral geniculate nucleus of the cat.

Abstract: The precision of the projection of the visual field to the dorsal lateral geniculate nucleus (LGNd) of the cat was studied by plotting the receptive fields of single neurons recorded extra-cellularly in the nucleus. The concepts of a ‘projection column’ and of ‘random scatter in the location of receptive fields’ have been defined in relation to cells in the LGNd. A projection column contains 90% of all the cells in the LGNd that have receptive fields with a common visual direction, the central axis of the column being the projection line for the given visual direction. In the region of the LGNd devoted to central vision the columns have a circular cross section and are about 1 mm in diameter.

The areas and layers of corticocortical terminations in the visual cortex of the Virginia opossum

Abstract: Visual cortex in the opossum was defined operationally as striate cortex and the total cortical area receiving ipsilateral projections from striate cortex. This area included all of Gray's ('24) peristriate cortex. In this study several areas were identified within Gray's striate and peristriate areas on the basis of changes in cytoarchitecture and parallel changes in thalamocortical fiber termination patterns. The layers of termination within these cortical areas, of the ipsilateral associational fibers, the commissural fibers and the thalamocortical fibers from the hemithalamus were determined by means of the Fink-Heimer stain. (1) Commissural fiber terminations occur in individual dense “bands” in certain regions of the different cytoarchitectural areas of visual cortex. These bands of commissural fiber terminations are separated by zones of cortex which receive only sparse commissural fiber terminations. The first band of commissural terminations is found in a zone of transitional cortex occupying lateral striate cortex and adjacent peristriate cortex. This band is characterized by terminations in all layers of cortex on the peristriate side and terminations circumscribing the lateral edge of layer IV on the striate side. A second commissural band of terminations lies in anterior and central peristriate areas with terminations in all layers except V. A cytoarchitectural delineation is present in central peristriate cortex between these two bands of commissural terminations. A third band with a laminar pattern of commissural terminations similar to the second band lies more laterally in other peristriate areas along the rhinal fissure and temporal cortex. These three bands broaden at their midpoints to fuse with one another. Commissural terminations are also found in a strip of peristriate cortex on the medial surface of the hemisphere. Characteristic of all commissural terminations in layer I is their restriction to the inner three-fourths of this layer. Subtotal lesions of visual cortex reveal homotopic and heterotopic commissural connections. Central striate cortex has few commissural interconnections. Most of this area receives a few commissural fiber terminations from the lateral portion of striate cortex and also from peristriate cortex. Fibers from the lateral region of striate cortex give rise to terminations which form the band about the striate border as may peristriate cortex adjacent to the lateral striate cortex border. Medial peristriate cortex has homotopic interconnections while the other peristriate areas have both heterotopic and homotopic interconnections. (2) the ipsilateral associational projections from striate cortex terminate mainly in layers I to IV in peristriate cortex. These terminations overlap the zones of peristriate cortex which receive sparse and dense commissural terminations. Degeneration in the lesioned hemisphere revealed tangential fibers in layer I that are present over a large extent of visual cortex. Thermal lesions of only layers I and II of striate cortex show that at least part of the ipsilateral association termination pattern arises from layer II. (3) In each cytoarchitectural area the corticocortical terminations are compared with the thalamocortical terminations and also with such axonal distributions described by Golgi and EM studies in other mammals. It is concluded that the visual cortex of the opossum has the cytoarchitectural subdivisions, and connectional substrate for at least two cortical representations of the visual field and that the fiber connections of the visual system of the opossum contain a basic organization present in other species.

Neurons and interneuronal connections of the central visual system

Abstract: 1. Neurons of the Central Visual System.- The Cortex and Lateral Geniculate Body.- Neuronal Structure of the Visual Cortex and Lateral Geniculate Body in Some Mammals.- Visual System of the Hedgehog (Insectivora).- Visual System of the Rabbit (Rodentia).- Visual System of the Dog (Carnivora).- Visual System of Monkeys (Primates).- Visual System of Man.- Size of the Neurons and Density of Their Arrangement.- Characteristics of the Layers of the Visual Cortex.- Similarities and Differences Between Neurons of Monkey and Man.- Distinctive Structural Features of Neurons in Areas 17, 18, and 19 of the Human Occipital Cortex.- 2. Connections Between Neurons and Details of Their Structure.- Endings and Branches of Axons.- Dendrites, Their Endings and Ramifications.- Varieties of Connections Between Neurons in the Cortical and Subcortical Parts of the Visual System.- Axo-dendritic Contacts of Cortical Pyramidal Cells.- Axo-somatic Connections of Cortical Pyramidal Cells.- Axo-dendritic Contacts of Cortical Stellate Cells.- Axo-somatic Contacts of Cortical Stellate Cells.- Axo-axonal Connections in the Cortex.- Axo-dendritic and Axo-somatic Contacts of Cells of the Lateral Geniculate Body.- Connections in the Retina.- Reality of the Systems of Spines on Dendrites Their Origin and Role.- Structure of Interneuronal Connections in the Cortex.- 3. Differences in Structure and Connections of the Visual System at Cortical and Subcortical Levels.- The Cortical Level.- Connections of Pyramidal Cells and Their Significance.- Connections of the Long-Axon Star Cells of Cajal.- Connections of Short-Axon Stellate Cells and Their Significance.- The Subcortical Level.- Neurons of the Lateral Geniculate Body.- The Main Differences Between Neurons of the Visual Cortex and Lateral Geniculate Body.- 4. Structure of the Central Visual System and Pathways.- Cortical Analyzer and Diffuse Elements.- Efferent Connections of the Visual Cortex.- Centrifugal Connections of the Retina.- A Scheme of the Structure of the Visual System.- 5. Specificity of Structure of the Central Visual System.- Structure of Neurons of the Visual System and Their Comparison with Other Neurons.- Specificity of Structure in Relation to the Problem of Color Vision.- New Data on the Structure and Function of the Lateral Geniculate Body in Primates Relative to the Problem of Color Vision.

The contribution of the dorsal lateral geniculate nucleus to the total pattern of thalamic terminations in striate cortex of the virginia opossum

Abstract: These studies were carried out to show the manner of projection of the dorsal lateral geniculate nucleus and other thalamic nuclei to striate cortex in the Virginia opossum. In order to demonstrate these projections, lesions were made in the dorsal lateral geniculate nucleus, in the ventral lateral geniculate nucleus, in most of the thalamus on one side except for the dorsal lateral geniculate nucleus, and in the entire unilateral thalamus. Following various survival times, usually seven days, the brains were appropriately prepared and stained with procedure I of the Fink-Heimer technique. Dorsal lateral geniculate neurons project in a topographical manner only to certain layers of striate cortex. These projections from the lateral geniculate are compared with the same system in other mammals, and it is concluded that it is similar in all mammals studied, except for the cat. In the cat the lateral geniculate projects beyond the border of striate cortex, but even in the cat the layers of termination within striate cortex are apparently similar. The ventral lateral geniculate nucleus does not project to visual cortex. Dorsal thalamic nuclei other dian the lateral geniculate project to peristriate cortex and to layers VI and I of striate cortex. The finding that thalamic nuclei, other than the lateral geniculate nucleus, project to striate cortex has never been described as part of the visual pathways in other mammals. It is suggested that these additional projections arise mainly from the lateral nuclear group of the thalamus in the opossum, and must be considered in relation to any response characteristics and organization of striate cells determined from physiological studies. These multiple thalamic projections can provide the substrate for more than one representation or “map” of sensory information in striate cortex.

Simple Cells of the Striate Cortex

Abstract: Publisher Summary This chapter provides an overview of the simple cells of the striate cortex. Cortical neurons have a hierarchical order where successive transformations of receptive field properties take place from simple up to higher-order hypercomplex cells. The properties of the more complex cells are derived from the convergence of afferents cells with simpler properties. The simple cells in Layer IV of the striate cortex are predominately of the stellate type. The neural pathways from the eyes are largely independent until they reach the level of the cortex and come together for the first time on the cells in the striate cortex. Because a majority of neurons in the striate cortex may be discharged from either eye, the possibility exists of producing a discharge via one eye and the testing for inhibition via the other. In the striate cortex of the cat or monkey, a number of classes of neurons exist—such as, simple, complex, hypercomplex, and, nonoriented.

Sequential change in receptive fields of striate neurons in dark adapted cats

Abstract: 1. A general purpose, digital computer was employed to map quantitatively the receptive fields of units in cat's striate cortex. 2. Receptive fields were studied as a function of barbiturate anesthetic level under dark adapted conditions. 3. Receptive fields obtained from lateral geniculate axons were topographically simple and usually represented a single peak with concentric zones of decreasing excitability. Such fields were stable under all anesthetic and electroencephalographic conditions. 4. Responses were recorded from striate cells, both simple and complex in the sense of Hubel and Wiesel. These demonstrated varied field configurations such as an excitatory cylinder in an inhibitory field, excitatory vertical axis flanked by asymmetric inhibitory areas, and more complex patterns including potentially direction and velocity sensitive ones. 5. Many cortical maps were unstable over time, especially in the presence of low voltage, fast electroencephalographic activity. Changes were not random nor did they represent simple linear displacements of peaks, but included axis shifts, gradient change, and expansion or contraction of excitatory and inhibitory zones with centers at fixed relative positions. 6. Heavy barbiturate anesthesia and spontaneous spindling in the EEG markedly reduced the variability in these maps; the encephale isole preparation was more stable than spinally intact animals. This association suggests a role of the midbrain reticular formation in cortical variability. 7. Random rather than iterative presentation of matrix points resulted in higher mean firing rates and more stable receptive fields, probably the result of photochemical recovery in dispersed receptors and time averaging of cellular excitability. 8. When stability was analyzed as a function of time interval of response (early on, late on, early off, late off), initial on responses were often more stable than longer latency late on- or off-responses. This factor, among others discussed, makes eye movement an unlikely explanation for map variability. It suggests additionally that late on- and off- responses represent input to the cortical cell from units other than those producing the early on-response. 9. The effects of pentobarbital, in addition to stabilization of the receptive field, included striking phase reversals in which inhibitory regions became excitatory and visa versa. Firing rate often changed substantially, but both increases and decreases were observed. 10. It is argued that visual response under pentobarbital is a special and not the general case of visual perception and that sequential receptive field changes during aroused brain states reflect integrative, purposive processes at the cortical level.

Is there lateral inhibition in the visual cortex

Abstract: AN acute angle appears to be less acute than it really is1,2. The effect has an obvious similarity to the tilt after-effect, the only difference in procedure being that the lines forming the acute angle are presented simultaneously in one case and successively in the other. Nevertheless, Blakemore et al.2 consider that the effect they studied is not the tilt after-effect, on the grounds of different temporal properties: their effect builds up and dissipates very rapidly, which, they argue, is inconsistent with known adaptation phenomena, such as Gibson after-effects3,4, which have long time constants.

Functional significance of arrangement of neurones in cell assemblies.

Abstract: An account is given of the columnar arrangement in the cerebral cortex that has been discovered for neurones having a similar receptivity. This has been observed in the somaesthetic cortex for neurones with similar modality sensitivities and in the visual cortex for neurones with similar directional sensitivities. The anatomical basis is discussed. In the motor cortex also there is an arrangement in clusters of pyramidal cells that are responsible for particular movements. The functional significance of this organization in clusters in the cerebral cortex is discussed in relationship to the problem of securing a reliable performance despite the irregular background discharge of the individual neurones. It is proposed that reliability is secured by the in-parallel arrangement of neurones with similar receptivities in the clusters. The neurones of a cluster tend to converge onto common target neurones, which, as it were, read out the summed performance of the cluster from moment to moment. Recent work on the cerebellum also discloses that there is an arrangement of Purkyně cells in clusters with somewhat similar receptive fields and that their axons tend to converge onto neurones of the cerebellar nuclei (fastigial nucleus), which likewise are arranged in functional clusters. The general concept emerges that the arrangement of neurones in clusters both in the cerebrum and in the cerebellum, achieves functional significance not only in giving opportunity for amplification and integration of incoming signals and for their sharpening by surround inhibition, but it is also important in the output performance. Signals are lifted out of noise by the spatial summation deriving from the many similarly performing neurones that project by their axons to the same cluster of target neurones; and this orderly projection can go on sequentially through all the complexities of on-going actions initiated by some input.