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Biomedical subjects

T N Wiesel

Publications and source records attributed to T N Wiesel.

At least 55 records · Page 3Linked to original sources
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.

Animals↗
PubMed1971

Aberrant visual projections in the Siamese cat.

1. Guillery has recently shown that the Siamese cat has a grossly abnormal lateral geniculate body. His anatomical study suggested that certain fibres originating in the temporal retina of each eye cross in the chiasm instead of remaining uncrossed. They thus reach the wrong hemispheres, but in the geniculate they terminate in the regions that the missing fibres from the ipsilateral eye would normally have occupied. The result is that each hemisphere receives an input from parts of the ipsilateral field of vision, this input being entirely from the opposite eye. The purpose of the present work was to study the physiological consequences of this aberrant projection, in the lateral geniculate body and visual cortex.2. Single-cell recordings from the lateral geniculate body confirmed the presence of projections from the ipsilateral visual field of the contralateral eye. The part of layer A(1) receiving these projections was arranged so that the receptive fields of the cells were situated at about the same horizontal level and at the same distance from the vertical meridian as the fields of cells in the layers above and below (layers A and B), but were in the ipsilateral visual field instead of the contralateral. They thus occupied a region directly across the mid line from their normal position.3. In the cortex of all animals studied, we found a systematic representation of part of the ipsilateral visual field, inserted between the usual contralateral representations in areas 17 and 18. When the visual cortex was crossed from medial to lateral the corresponding region of visual field moved from the contralateral periphery to the mid line, and then into the ipsilateral field for 20 degrees . The movement then reversed, with a return to the mid line and a steady progression out into the contralateral field. The entire double representation was, with some possible exceptions, a continuous one. The point of reversal occurred at or near the 17-18 boundary, as judged histologically, and this boundary was in about the same position as in ordinary cats.4. Cells in the part of the cortex representing the ipsilateral fields had normal receptive fields, simple, complex, or hypercomplex. These fields tended to be larger than those in corresponding parts of the contralateral visual fields. Receptive-field size varied with distance from the area centralis, just as it does in the normal cat, so that cells with the smallest fields, in the area centralis projection, were situated some distance from the 17-18 border.5. Projections originating from the first 20 degrees from the midvertical in both visual half-fields had their origin entirely in the contralateral eye, as would be expected from the abnormal crossing at the chiasm. Beyond this visual-field region, and out as far as the temporal crescents, there were projections from both eyes, but we found no individual cells with input from the two eyes. The cells were aggregated, with some groups of cells driven by one eye and some by the other.6. From previous work it is known that ordinary cats raised with squint show a decline in the proportion of cells that can be driven binocularly, whereas animals raised with both eyes closed show little or no decline. A Siamese cat raised with both eyes closed had binocular cells in the regions of 17 and 18 subserving the peripheral visual fields, suggesting that the absence of binocular cells seen in the other Siamese cats was indeed secondary to the squint.7. In two Siamese cats there were suggestions of an entirely different projection pattern, superimposed upon that described above. In the parts of 17 and 18 otherwise entirely devoted to the contralateral visual field, we observed groups of cells with receptive fields in the ipsilateral field of vision. The electrode would pass from a region where cells were driven from some part of the contralateral visual field, to regions in which they were driven from a part of the ipsilateral field directly opposite, across the vertical mid line. The borders of these groups were not necessarily sharp, for in places there was mixing of the two groups of cells, and a few cells had input from two discrete regions located opposite one another on either side of the vertical mid line. The two receptive-field components of such cells were identical, in terms of orientation, optimum direction of movement, and complexity. Stimulation of the two regions gave a better response than was produced from either one alone, and the relative effectiveness of the two varied from cell to cell. These cells thus behaved in a way strikingly reminiscent of binocular cells in common cats.8. The apparent existence of two competing mechanisms for determining the projection of visual afferents to the cortex suggests that a number of factors may cooperate in guiding development. There seems, furthermore, not to be a detailed cell-to-cell specificity of geniculocortical connexions, but rather a tendency to topographic order and continuity, with one part of a given area such as 17 able to substitute for another. Whether or not these tentative interpretations are ultimately proved correct, it seems clear that this type of genetic anomaly has potential usefulness for understanding mechanisms of development of the nervous system.

Animals↗
PubMed1970

The period of susceptibility to the physiological effects of unilateral eye closure in kittens.

1. Kittens were visually deprived by suturing the lids of the right eye for various periods of time at different ages. Recordings were subsequently made from the striate cortex, and responses from the two eyes compared. As previously reported, monocular eye closure during the first few months of life causes a sharp decline in the number of cells that can be influenced by the previously closed eye.2. Susceptibility to the effects of eye closure begins suddenly near the start of the fourth week, remains high until some time between the sixth and eighth weeks, and then declines, disappearing finally around the end of the third month. Monocular closure for over a year in an adult cat produces no detectable effects.3. During the period of high susceptibility in the fourth and fifth weeks eye closure for as little as 3-4 days leads to a sharp decline in the number of cells that can be driven from both eyes, as well as an over-all decline in the relative influence of the previously closed eye. A 6-day closure is enough to give a reduction in the number of cells that can be driven by the closed eye to a fraction of the normal. The physiological picture is similar to that following a 3-month monocular deprivation from birth, in which the proportion of cells the eye can influence drops from 85 to about 7%.4. Cells of the lateral geniculate receiving input from a deprived eye are noticeably smaller and paler to Nissl stain following 3 or 6 days' deprivation during the fourth week.5. Following 3 months of monocular deprivation, opening the eye for up to 5 yr produces only a very limited recovery in the cortical physiology, and no obvious recovery of the geniculate atrophy, even though behaviourally there is some return of vision in the deprived eye. Closing the normal eye, though necessary for behavioural recovery, has no detectable effect on the cortical physiology. The amount of possible recovery in the striate cortex is probably no greater if the period of eye closure is limited to weeks, but after a 5-week closure there is a definite enhancement of the recovery, even though it is far from complete.

Age Factors↗
PubMed1970

Consequences of monocular deprivation on visual behaviour in kittens.

1. Kittens were raised for a period with one of their eyes closed by suture of the lids. The age at suture and the duration of deprivation were varied systematically. When the cat was a year or more old, the normal and deprived eyes were compared using behavioural procedures which made graded demands on visual function.2. In kittens deprived from birth, the duration of eye closure determined the severity of the defect in vision with the deprived eye. A cat with an eye closed for the first 4-6 weeks showed as a permanent effect only a lowering of the visual acuity. When closure was extended through the first 7 weeks the visual acuity was further lowered but the animal still showed good visual guidance of paw placement. Further extension of deprivation through the first 16 weeks led to a still more severe defect; such animals showed no indication of visual guidance of paw placement or of pattern discrimination. They were influenced visually by stimuli that differed in luminosity.3. The upper age limit of the susceptibility to deprivation was determined by varying the age at eye closure. Waiting until 1 month of age before closing the eye conferred no appreciable protection. Waiting until 2 months of age, however, reduced the damage. Deprivation starting at 4 months of age or later produced no effect we could detect. Thus, susceptibility is greatest during the second month after birth and then falls until by 4 months of age the kitten, like the adult cat, suffers no permanent consequences of monocular light and form deprivation.4. After exclusive use of the deprived eye for a period, brought about by closure of the normal eye, visual control with the deprived eye was better than in similarly deprived cats whose normal eye was never closed. Improvement in the deprived eye was also seen in an animal whose normal eye was closed after both eyes had been open for more than one year.5. Relating the behavioural results to the neurophysiological findings in the visual cortex in the same or similarly deprived cats shows that the grading of visual defects with age and length of deprivation was generally paralleled by a change in proportion of cortical cells driven by stimulation of the deprived eye. The effect of reversal of eye closure in improving behavioural control was not, however, accompanied by an increase in the ability of the deprived eye to drive cortical cells.

Age Factors↗
PubMed1969

Visual area of the lateral suprasylvian gyrus (Clare-Bishop area) of the cat.

On anatomical and physiological grounds a zone of cat cortex deep in the medial bank of the suprasylvian sulcus (the Clare-Bishop area) is known to receive strong visual projections both from the lateral geniculate body and area 17. We have mapped receptive fields of single cells in this area in eight cats. Active responses to visual stimuli were found over most of the medial bank of the suprasylvian sulcus extending to the depths and over to the lowest part of the lateral bank. The area is clearly topographically arranged. The first responsive cells, recorded over the lateral convexity and 2-3 mm down the medial bank, had receptive fields in the far periphery of the contralateral visual fields. The receptive fields tended to be large, but showed considerable variation in size and scatter in their positions. As the electrode advanced down the bank, fields of successively recorded cells gradually tended to move inwards, so that in the depths of the sulcus the inner borders of many of the fields reached the vertical mid line. Here the fields were smaller, though they still varied very much in size. Receptive fields were larger than in 17, 18, or 19, but otherwise were not obviously different from the complex and lower-order hypercomplex fields in those areas. No simple fields, or concentric fields of the retino-geniculate type, were seen. Cells with common receptive-field orientation were grouped together, but whether or not the grouping occurs in columns was not established. Most cells were driven independently by the two eyes. Fields in the two eyes seemed to be identical in organization. Cells dominated by the contralateral eye were much more common than ipsilaterally dominated ones, but when cells with parafoveal and peripheral fields were considered separately, the asymmetry was seen to apply mainly to cells with peripheral fields.

Animals↗
PubMed1968

Receptive fields and functional architecture of monkey striate cortex.

1. The striate cortex was studied in lightly anaesthetized macaque and spider monkeys by recording extracellularly from single units and stimulating the retinas with spots or patterns of light. Most cells can be categorized as simple, complex, or hypercomplex, with response properties very similar to those previously described in the cat. On the average, however, receptive fields are smaller, and there is a greater sensitivity to changes in stimulus orientation. A small proportion of the cells are colour coded.2. Evidence is presented for at least two independent systems of columns extending vertically from surface to white matter. Columns of the first type contain cells with common receptive-field orientations. They are similar to the orientation columns described in the cat, but are probably smaller in cross-sectional area. In the second system cells are aggregated into columns according to eye preference. The ocular dominance columns are larger than the orientation columns, and the two sets of boundaries seem to be independent.3. There is a tendency for cells to be grouped according to symmetry of responses to movement; in some regions the cells respond equally well to the two opposite directions of movement of a line, but other regions contain a mixture of cells favouring one direction and cells favouring the other.4. A horizontal organization corresponding to the cortical layering can also be discerned. The upper layers (II and the upper two-thirds of III) contain complex and hypercomplex cells, but simple cells are virtually absent. The cells are mostly binocularly driven. Simple cells are found deep in layer III, and in IV A and IV B. In layer IV B they form a large proportion of the population, whereas complex cells are rare. In layers IV A and IV B one finds units lacking orientation specificity; it is not clear whether these are cell bodies or axons of geniculate cells. In layer IV most cells are driven by one eye only; this layer consists of a mosaic with cells of some regions responding to one eye only, those of other regions responding to the other eye. Layers V and VI contain mostly complex and hypercomplex cells, binocularly driven.5. The cortex is seen as a system organized vertically and horizontally in entirely different ways. In the vertical system (in which cells lying along a vertical line in the cortex have common features) stimulus dimensions such as retinal position, line orientation, ocular dominance, and perhaps directionality of movement, are mapped in sets of superimposed but independent mosaics. The horizontal system segregates cells in layers by hierarchical orders, the lowest orders (simple cells monocularly driven) located in and near layer IV, the higher orders in the upper and lower layers.

Animals↗