Meynert cells in the primate visual cortex

The solitary cells of Meynert are distinguished by their specific location in layer V of the striate cortex, very large size, argyrophilia, and the profusion of neurofilaments in their dendrites and perikarya. They occur with greater frequency in the macular region of the cortex, spaced a minimal distance of 110 mum apart, at a maximum density of about 8000/cm-2. In the perifoveal cortex, Meynert cells are spaced about 400 mum apart and packed at a density of approximately 625/cm-2. Each Meynert cell has an apical dendrite and many large basal dendrites. The perikaryon and primary segments of all dendrites are spine-free; however, more distally a total of 36 000 spines are present, differentially disposed upon the dendritic surfaces. The basal dendrites bear over 77% of the spines on the Meynert cell, although they account for only 66% of the total length of the dendritic arborization. The first part of the apical dendrite is the most densely decorated with appendages, accounting for almost 10% of the spines on the whole dendritic tree. The apical dendrite becomes progressively less spiny as it passes through the superficial part of layers IV and III; less than 2.5% of the total number of spines of the Meynert cell project from this part of the apical dendrite. When the dendrite reaches layer II it bursts into an umbel of rapidly tapering branches. These are highly spinose, accounting for 8-13% of the cell's total, dispersed over only 23% of the linear dendritic length. It is suggested that this differential distribution of thorns can be correlated with the axonal inputs in the various cortical layers, and that the Meynert cell is designed to receive maximal information from layers I and II, and from layers V and VI, which are sources mainly of intracortical inputs. Thus the Meynert cell may be principally concerned with integrative information. In the perifoveal cortex, the basal dendrites of adjacent Meynert cells overlap considerably, and the apical terminal bouquet dendrites do not. In the macular cortex, because of the increased frequency of these neurons, both basaal and apical terminal dendritic fields overlap. A model is developed to illustrate these hypotheses.

Cells responding to changing image size and disparity in the cortex of the rhesus monkey

1. The cells of the cortex of the posterior bank of the superior temporal sulcus of the monkey appear to be specialized to signal motion in the visual field. In this paper, cells in this cortical area capable of signalling motion towards or away from the animal are described.2. Two such types of cell were encountered. One type, the opposed movement complex and opposed movement hypercomplex cells, responded to two edges at a given orientation moving towards or away from each other within the receptive fields. These cells were driven either monocularly or binocularly, but when binocularly driven the cells responded in an identical manner to stimulation of each eye, thus suggesting that such cells must receive a double, and opposed, input from each eye. The other type of cell, always binocularly driven, responded to movement in opposite directions on the two retinas, thus suggesting that such cells must receive diametrically opposite connexions from the two eyes.3. Long penetrations made to study the manner in which such cells were grouped together in the cortex revealed that they were arranged in small groups or clusters, separated from each other by the common directionally selective cells so prominently present in this area. Thus, cells with one type of wiring mechanism were separated from each other by cells receiving another, and more common, type of anatomical wiring.

Cell structure and function in the visual cortex of the cat

1. The organization of the visual cortex was studied with a technique that allows one to determine the physiology and morphology of individual cells. Micro-electrodes filled with the fluorescent dye Procion yellow were used to record intracellularly from cells in area 17 of the cat. The visual receptive field of each neurone was classified as simple, complex, or hypercomplex, and the cell was then stained by the iontophoretic injection of dye.2. Fifty neurones were successfully examined in this way, and their structural features were compared to the varieties of cell types seen in Golgi preparations of area 17. The majority of simple units were stellate cells, whereas the majority of complex and hypercomplex units were pyramidal cells. Several neurones belonged to less common morphological types, such as double bouquet cells. Simple cells were concentrated in layer IV, hypercomplex cells in layer II + III, and complex cells in layers II + III, V and VI.3. Electrically inexcitable cells that had high resting potentials but no impulse activity were stained and identified as glial cells. Glial cells responded to visual stimuli with slow graded depolarizations, and many of them showed a preference for a stimulus orientation similar to the optimal orientation for adjacent neurones.4. The results show that there is a clear, but not absolute correlation between the major structural and functional classes of cells in the visual cortex. This approach, linking the physiological properties of a single cell to a given morphological type, will help in furthering our understanding of the cerebral cortex.

Opponent-colour cells in different layers of foveal striate cortex

1. The majority of cells in layer 4B have opponent-colour properties indicating that colour opponency plays an important role in the early stages of visual processing in foveal striate cortex. In contrast to cells in the lateral geniculate nucleus many of these cells receive centre-surround antagonism from the same cone mechanism. Some cells show this spatial antagonism at threshold; others require suprathreshold stimuli for its demonstration.2. The majority of cells in layer 4B do not show orientation or directional selectivity. The proportion of cells with orientation and directional selectivity increases and the proportion of opponent-colour cells decreases with increasing distance above and below layer 4B so that the majority of cells in the outer layers exhibit considerable spatial selectivity without apparent colour opponency. These changing proportions suggest that the latter cells may be receiving their inputs from different types of opponent-colour cells making them sensitive to different types of colour contrast but not to colour per se.3. More opponent-colour cells receive inputs from the red- and green- sensitive cone mechanisms than from the blue-sensitive one. This difference is more marked in layer 4B than 3B suggesting that the latter cortical layer may be more involved in colour vision than the former.

Interocular transfer of a visual after-effect in normal and stereoblind humans

1. Following inspection of a high contrast grating a test grating of a slightly different orientation will briefly appear rotated from its true orientation in a direction opposite to that of the adapting grating.2. The extent of interocular transfer of this phenomenon (the tilt after-effect) was measured in a number of normal subjects and in four subjects (three of whom had a strabismus) who lacked stereopsis.3. In contrast to the normal subjects, none of the four stereoblind subjects showed any interocular transfer of the tilt after-effect. Amongst the normal subjects the extent of transfer of this after-effect was positively correlated with the subject's stereoacuity. Maximum transfer (70%) was found in the subject with the best stereoacuity. In many subjects transfer was greater from the dominant eye to the non-dominant eye than vice versa.4. By analogy with experiments on cats deprived of congruent visual input to the two eyes early in life it is argued that the stereoblind subjects lack any binocularly driven cortical neurones.

Neurons in rhesus monkey visual cortex: systematic relation between time of origin and eventual disposition

Autoradiographic evidence after injection of tritiated thymidine indicates that cell position in the laminae of the monkey visual cortex is systematically related to time of cell orgin. The earliest-formed neurons, destined for the deepest stratum, arise at about embryonic day 45, and the last ones, destined for the outermost cell stratum, form at about day 102; cells of intervening layers are generated at intervening times. No neocortical neurons are produced in the last two prenatal months or after birth. Compared to cortical neurons in rodents, those in the monkey arise earlier, and the "inside-out" relation of cell position to time of origin is more rigid.

Neural correlate of perceptual adaptation to gratings

Exposure of simple cells of the cat striate cortex to high-contrast drifting gratings greatly reduces the subsequent response of the cells to low-contrast gratings. This adaptation effect has an average duration of 30 seconds and shows interocular transfer and selectivity for spatial frequency and orientation. This effect is strikingly similar to the perceptual adaptation to high-contrast gratings.

Visual experience without lines: effect on developing cortical neurons

Kittens were reared in a planetarium-like visual environment that lacked straight line contours. Cortical neurons were subsequently highly sensitive to spots of light but not to straight lines, in marked contrast to those from a normal cat. If linear contour processing is an innate function it appears to be subject to substantial modification by early visual experience.

Gamma-aminobutyric acid antagonism in visual cortex: different effects on simple, complex, and hypercomplex neurons

Intravenous bicuculline was used to examine how removing gamma-aminobutyric acid-mediated inhibition affects the visual response properties of single cortical neurons. Simple neurons were depressed and complex neurons showed increase in the vigor and range of responses. Hypercomplex cells were no longer inhibited by elongated stimuli. The results are consistent with present evidence concerning the origin and distribution of inhibitory connections within the cortex.