Receptive-field properties of different classes of neurons in visual cortex of normal and dark-reared cats.
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Animals↗
Biomedical subjects
A G Leventhal
Publications and source records attributed to A G Leventhal.
Geniculate input to cat visual cortex: a comparison of area 19 with areas 17 and 18.
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Animals↗
Evidence that the different classes of relay cells of the cat's lateral geniculate nucleus terminate in different layers of the striate cortex.
Small electrophoretic injections of horseradish peroxidase (HRP) were made with recording microelectrodes in different layers of area 17 of the cat. The sizes and locations of labeled relay cells in the lateral geniculate nucleus (LGNd) were then studied. Layer I was found to receive inputs mainly from small LGNd cells (13--21 micrometer). These cells were located in the parvocellular C laminae and the MIN. Layer II and the upper portion of layer III were not found to receive LGNd afferents. Lower layer III was found to receive inputs mainly from small to medium-sized relay cells. These cells were located in the A laminae and the parvocellular C laminae. Layer IVab and the layer III--IV border region were found to receive afferents from predominantly large LGNd neurons (greater than 20 micrometers). These cells were located in alminae A, A1, C, and the MIN. Layer IVc was found to receive inputs from mostly small to medium-sized cells (15--23 micrometer). Nearly all of these cells were in the A laminae although some small cells in laminae C were observed following layer IVc injections which involved the layer IV--V border region. Layer V, away from the layer IV--V border region, was not found to receive LGNd afferents. Finally, layer VI was found to receive inputs from both large and small relay cells. These cells were all located in the A laminae. In the light of previous findings, these results suggest that the terminals of W, X, and Y cell axons are segregated within the cat's striate cortex: W cells projecting to layer 1, the deeper portion of layer III and the layer IV--V border region; X cells projecting heavily to layer IVc with a minor projection to layer VI and possibly also to lower layer III; Y cells projecting heavily to layer IVab and the layer III-IV border region with a smaller projection to layer VI.
Animals↗
Brain stem afferents to visual cortical areas 17, 18 and 19 in the cat, demonstrated by horseradish peroxidase.
The origins of brain stem projections to the cytoarchitectonically different areas 17, 18 and 19 of the cat's visual cortex were studied following small horseradish peroxidase (HRP) injections. Labelled cells were counted in a dopaminergic nucleus (nucleus linearis rostralis (NLR)), other catecholaminergic nuclei (locus coeruleus, parabrachialis nuclei and nucleus subcoeruleus) and serotonergic nuclei (nucleus raphe dorsalis (NRD) and nucleus centralis superior (NCS)). Area 18 receives afferents from more locus coeruleus cells than either of areas 17 or 19. The number of labelled cells in the catecholaminergic nuclei far exceeds that in the serotonergic nuclei.
Afferent Pathways↗
Physiological consequences for the cat's visual cortex of effectively restricting early visual experience with oriented contours.
1. The early visual experience of nine cats was restricted to viewing horizontal or vertical lines inside opaque goggles. 2. When the kittens were 3-4 mo old, extracellular recordings were made in the primary visual cortex. To obtain a representative sample of cortical cells, units were studied at regularly spaced intervals along the course of electrode penetrations traveling oblique to the cortical surface. An automated assessment of preferred orientation using a computer-driven optical display was employed, and during the recording session the experimenters did not know which orientation(s) each animal had viewed in early life. 3. In the cats that viewed horizontal lines with one eye and vertical lines with the other during rearing, two major findings of previous workers (14) were confirmed. First, a majority of units were not selective for orientation. Second, units with preferred orientations near vertical tended to be activated exclusively by the eye that had viewed vertical, and likewise for horizontal. 4. In cats that viewed lines of the same orientation with both eyes during rearing, a substantially smaller proportion of units were selective for orientation; the preferred orientations of these units also tended to match the orientation to which the cats had been exposed. 5. Portions of some electrode penetrations showed an orderly arrangement of cells according to preferred orientation similar to that seen in normal cats, but with regions over which only nonselective cells were found. Many penetrations appeared less orderly. 6. The results are consistent with a role for early visual experience in maintaining the responsiveness and innate selectivity of cortical neurons, although they cannot entirely rule out the possibility that experience may alter or determine the preferred orientation of some cells.
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Receptive-field properties of neurons in different laminae of visual cortex of the cat.
1. Receptive-field properties of neurons in the different layers of the visual cortex of normal adult cats were analyzed quantitatively. Neurons were classified into one of two groups: 1) S-cells, which have discrete on- and/or off-regions in their receptive fields and possess inhibitory side bands; 2) C-cells, which do not have discrete on- and off-regions in their receptive fields but display an on-off response to flashing stimuli. Neurons of this type rarely display side-band inhibition. 2. As a group, S-cells display lower relative degrees of binocularity and are more selective for stimulus orientation than C-cells. In addition, within a given lamina the S-cells have smaller receptive fields, lower cutoff velocities, lower peak responses to visual stimulation, and lower spontaneous activity than do the C-cells. 3. S-cells in all layers of the cortex display similar orientation sensitivities, mean spontaneous discharge rates, peak response to visual stimulation, and degrees of binocularity. 4. Many of the receptive-field properties of cortical cells vary with laminar location. Receptive-field sizes and cutoff velocities of S-cells and of C-cells are greater in layers V and VI than in layers II-IV. For S-cells, preferred velocities are also greater in layers V and VI than in layers II-IV. Furthermore, C-cells in layers V and VI display high mean spontaneous discharge rates, weak orientation preferences, high relative degrees of binocularity, and higher peak responses to visual stimulation when compared to C-cells in layers II and III. 5. The receptive-field properties of cells in layers V-VI of the striate cortex suggest that most neurons that have their somata in these laminae receive afferents from LGNd Y-cells. Hence, our results suggest that afferents from LGNd Y-cells may play a major part in the cortical control of subcortical visual functions.
Afferent Pathways↗
Effects of early experience upon orientation sensitivity and binocularity of neurons in visual cortex of cats.
The class of neurons within the visual cortex of normal adult cats that has the smallest receptive fields (less than or equal to 2.25 degrees2) and that responds only to low rates of stimulus motion (less than or equal to 50 degrees / sec) responds preferentially to lines oriented about either the horizontal axis (+/-22.5 degrees) or the vertical axis (+/-22.5 degrees). In animals reared without exposure to patterned visual stimulation, many of these cells display orientation preferences but are activated monocularly. In contrast, in normal animals, neurons that have larger receptive fields or that respond to higher rates of stimulus motion do not exhibit a similar bias in the distribution of their orientation preferences. Cells of this type, studied in animals reared without exposure to patterned visual stimuli, are activated binocularly but do not display orientation preferences.
Animals↗
Cortical effect of early selective exposure to diagonal lines.
Neurons in the visual cortex that respond preferentially to diagonal contours are present only in cats exposed to diagonal lines early in life. In contrast, cells that prefer horizontal or vertical contours are found following exposure to horizontal, to vertical, and to diagonal lines. Such cells do not require a specific visual input for maintenance or for development; neurons responding preferentially to diagonal lines do.
Age Factors↗
Selective depletion of beta cells affects the development of alpha cells in cat retina.
The results of previous studies suggest that class-specific interactions contribute to the development of the different classes of retinal ganglion cells. We tested this hypothesis by examining the morphologies and distributions of alpha (alpha) cells in regions of mature cat retina selectively depleted of beta (beta) cells as a result of visual cortex lesions at birth. We find that alpha cells in regions of central retina depleted of beta cells are abnormally large while alpha cells in regions of peripheral retina depleted of beta cells are abnormally small. The normal central-to-peripheral alpha cell soma-size gradient is absent in hemiretinae depleted of beta cells. The dendritic fields of alpha cells in the border of beta-cell-depleted hemiretina extend preferentially into the beta-cell-poor hemiretina. In spite of this, alpha cell bodies retain their normal retinal distribution and remain distributed in a nonrandom mosaic-like pattern. Thus, it appears that the development of alpha retinal ganglion cells is influenced by interactions both with other alpha cells (class-specific interactions) and with surrounding beta cells (nonclass-specific interactions).
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Direction-sensitive X and Y cells within the A laminae of the cat's LGNd.
Drifting sinusoidal gratings, moving bars, and moving spots were employed to study the direction sensitivity of 425 neurons in the A laminae of the cat's LGNd. Thirty-two percent of X- and Y-type LGNd relay cells exhibit significant direction sensitivity when tested with drifting sinusoidal gratings. X and Y cells exhibit the same degree of direction sensitivity. Moving spots and bars elicit direction specific responses from LGNd cells that are consistent with those elicited when drifting sinusoidal gratings are employed. For cells that are both orientation and direction sensitive, the preferred direction tends to be orthogonal to the preferred orientation. In general, direction sensitivity is strongest at relatively low spatial frequencies, well below the spatial-frequency cutoff for the cell. The presence of significant numbers of direction-sensitive LGNd cells raises the possibility that subcortical direction specificity is important for the generation of this property in the visual cortex.
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Stimulus dependence of orientation and direction sensitivity of cat LGNd relay cells without cortical inputs: a comparison with area 17 cells.
The cortical contribution to the orientation and direction sensitivity of LGNd relay cells was investigated by recording the responses of relay cells to drifting sinusoidal gratings of varying spatial frequencies, moving bars, and moving spots in cats in which the visual cortex (areas 17, 18, 19, and LS) was ablated. For comparison, the spatial-frequency dependence of orientation and direction tuning of striate cortical cells was investigated employing the same quantitative techniques used to test LGNd cells. There are no significant differences in the orientation and direction tuning to relay cells in the LGNd of normal and decorticate cats. The orientation and direction sensitivities of cortical cells are dependent on stimulus parameters in a fashion qualitatively similar to that of LGNd cells. The differences in the spatial-frequency bandwidths of LGNd cells and cortical cells may explain many of their differences in orientation and direction tuning. Although factors beyond narrowness of spatial-frequency tuning must exist to account for the much stronger orientation and direction preferences of cells in area 17 when compared to LGNd cells, the evidence suggests that the orientation and direction biases present in the afferents to the visual cortex may contribute to the orientation and direction selectivities found in cortical cells.
Animals↗
Neural correlates of boundary perception.
The responses of neurons in areas V1 (17) and V2 (18) of anesthetized and paralyzed rhesus monkeys and cats were recorded while presenting a set of computer-generated visual stimuli that varied in pattern, texture, luminance, and contrast. We find that a class of extrastriate cortical cells in cats and monkeys can signal the presence of boundaries regardless of the cue or cues that define the boundaries. These cue-invariant (CI) cells were rare in area V1 but easily found in V2. CI cortical cells responded more strongly to more salient boundaries regardless of the cue defining the boundaries. Many CI cortical cells responded to illusory contours and exhibited the same degree of orientation and direction selectivity when tested with boundaries defined by different cues. These cells have significant computational power inherent in their receptive fields since they were able to generalize across stimuli and integrate multiple cues simultaneously in order to signal boundaries. Cells in higher order cortical areas such as MT (Albright, 1992), MST (Geesaman & Anderson, 1996), and IT (Sary et al., 1993) have previously been reported to respond in a cue invariant fashion. The present results suggest that the ability to respond to boundaries in a cue-invariant manner originates at relatively early stages of cortical processing.
Animals↗