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.

Retinal ganglion cell classes in the Old World monkey: morphology and central projections.

Labeled ganglion cells were studied in whole-mount retinas of Old World monkeys after electrophoretic injections of horseradish peroxidase into physiologically characterized sites. A number of different morphological classes have been identified, each of which has a distinctive pattern of central projection. Since different functional classes of primate retinal ganglion cells also have distinctive patterns of central projection, correspondences between functional and morphological cell types have been inferred. There prove to be parallels between morphological types of cat monkey ganglion cells.

Abnormal visual pathways in normally pigmented cats that are heterozygous for albinism.

The various forms of albinism affect about one in 10,000 births in the United States. An additional 1 to 2 percent of the population has normal pigmentation but is heterozygous and carries a recessive allele for albinism. The retinogeniculocortical pathways were studied in normally pigmented cats that carry a recessive allele for albinism. The cats exhibited abnormalities in their visual pathways similar to those present in homozygous albinos. These results imply that visual anomalies like those found in albinos may be present in 1 to 2 percent of the human population.

The nasotemporal division in primate retina: the neural bases of macular sparing and splitting.

In primates, each hemisphere contains a representation of the contralateral visual hemifield; unilateral damage to the visual pathways results in loss of vision in half of the visual field. Apparently similar severe, unilateral lesions to the central visual pathways can result in two qualitatively different central visual field defects termed macular sparing and macular splitting. In macular sparing a 2 degrees to 3 degrees region around the fovea is spared from the effects of unilateral damage to the visual pathways. In macular splitting there is no such spared region and the scotoma produced by unilateral brain damage bisects the fovea. The patterns of decussation of the different classes of retinal ganglion cells in both New World (Saimiri sciureus) and Old World (Macaca fascicularis) monkeys have been determined by horseradish peroxidase injection. In both species the distributions of ipsilaterally and contralaterally projecting ganglion cells in the central retina are different from those in other mammals and suggest neural bases for macular sparing and splitting, respectively.

Aging affects contrast response functions and adaptation of middle temporal visual area neurons in rhesus monkeys.

In the present study we studied the effects of aging on the coding of contrast in area V1 (primary visual cortex) and MT (middle temporal visual area) of the macaque monkey using single-neuron in vivo electrophysiology. Our results show that both MT and V1 neurons in old monkeys are less sensitive to contrast than those in young monkeys. Generally, contrast sensitivity is affected by aging more severely in MT cells than in V1 cells. Specifically, MT cells were affected more severely than motion direction selective V1 cells. Particularly, we found that MT neurons in old monkeys exhibited enhanced maximum visual responses, higher levels of spontaneous activity and decreased signal-to-noise ratios. In addition, we also found age-related changes in neuronal adaptation to visual motion in MT. Compared with young animals, the contrast gain of MT neurons in old monkeys is less affected, but the response gain by adaptation of MT neurons is more affected. Our results suggest that there may be an anomalous visual processing in both the magnocellular and parvocellular pathways. The neural changes described here are consistent with an age-related degeneration of intracortical inhibition and could underlie some deficits in visual function during normal aging.

Degradation of stimulus selectivity of visual cortical cells in senescent rhesus monkeys.

Human visual function declines with age. Much of this decline is probably mediated by changes in the central visual pathways. We compared the stimulus selectivity of cells in primary visual cortex (striate cortex or V1) in young adult and very old macaque monkeys using single-neuron in vivo electrophysiology. Our results provide evidence for a significant degradation of orientation and direction selectivity in senescent animals. The decreased selectivity of cells in old animals was accompanied by increased responsiveness to all orientations and directions as well as an increase in spontaneous activity. The decreased selectivities and increased excitability of cells in old animals are consistent with an age-related degeneration of intracortical inhibition. The neural changes described here could underlie declines in visual function during senescence.

Functional degradation of extrastriate visual cortex in senescent rhesus monkeys.

The receptive field properties of striate cortical (V1) cells degrade in senescent macaque monkeys. We have now carried out extracellular single unit studies of the receptive field properties of cells in extrastriate visual cortex (area V2) in very old rhesus (Macaca mulatta) monkeys. This study provides evidence that both the orientation and direction selectivities of V2 cells in old monkeys degrade significantly. Decreased selectivity is accompanied by increased visually driven and spontaneous responses. As a result, V2 cells in old animals exhibit markedly decreased signal-to-noise ratios. A significant degradation of neural function in extrastriate cortex may underlie the declines in higher order visual function that accompany normal aging.

Relationship between preferred orientation and receptive field position of neurons in cat striate cortex.

It has been known for two decades that neurons in mammalian visual cortex respond selectively to stimuli falling on the retina at a particular angular orientation (Hubel and Wiesel, '62). Recent evidence suggests that most cat retinal ganglion cells (Levick and Thibos, '82) and relay cells (Vidyasagar and Urbas, '82) in the cat's dorsal lateral geniculate nucleus are also orientation selective. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis, most retinal ganglion cells have oriented dendritic fields (Leventhal and Schall, '83) and respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick an Thibos, '82). This relationship is strongest close to the horizontal meridian (the visual streak) of the retina (Leventhal and Schall, '83). To determine if a relationship between preferred orientation and polar angle exists in visual cortex, the preferred orientations and receptive field positions of 768 striate cortical neurons were studied. As in the retina, a systematic relationship exists between preferred orientation and visual field position in area 17. In parts of striate cortex 15--80 degrees from the area centralis projection there is a strong tendency for cells to respond best to lines oriented radially. In regions 4--15 degrees from the area centralis projection this relationship appears weaker. In regions subserving the central 4 degrees of visual angle no such relationship exists. Throughout area 17 the relationship between preferred orientation and polar angle is strongest in regions subserving the horizontal meridian.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal development of different classes of cat retinal ganglion cells.

Previous investigators have documented the postnatal development of alpha and beta type ganglion cells in cat retinae (Ramoa et al. [1987] Science 237:522-525; Ramoa et al. [1988] J. Neurosci. 8:4239-4261; Dann et al. [1987] Neurosci. Lett. 80:21-26; Dann et al. [1988] J. Neurosci. 8(5):1485-1499). The development of the remaining cells (about 50%), which constitute a heterogeneous group and are referred to here collectively as gamma cells (Boycott and Wässle, '74), has not been studied in detail. The purpose of this study was to compare the postnatal development of alpha, beta, and gamma cells in kitten and adult retinae using horseradish peroxidase histochemistry and the fluorescent dye DiI. In the kitten, alpha, beta, and gamma cells are recognizable. We find, as have others, that kitten alpha and beta cell bodies and dendritic fields are significantly smaller than in the adult. However, kitten gamma cells are nearly adult sized. In fact, at birth the cell bodies of beta cells throughout the retina are significantly smaller than those of gamma cells. During the first 12 weeks of life, alpha and beta cell bodies increase in size from 90% to 680% depending upon eccentricity. Gamma cells hardly increase in size at all. Also, the normal adult center-to-peripheral cell size gradient for alpha and beta cells is not seen in the neonate. Gamma cells show no such gradient in the neonate or adult. Our results suggest that the morphological development of alpha and beta cells occurs later than that of gamma cells and may explain some of the differences in the effects of visual deprivation and surgical manipulation upon the parallel Y-, X-, and W-cell pathways.

Structural basis of orientation sensitivity of cat retinal ganglion cells.

We investigated the structural basis of the physiological orientation sensitivity of retinal ganglion cells (Levick and Thibos, '82). The dendritic fields of 840 retinal ganglion cells labeled by injections of horseradish peroxidase into the dorsal lateral geniculate nucleus (LGNd) or optic tracts of normal cats. Siamese cats, and cat deprived of patterned visual experience from birth by monocular lid-suture (MD) were studied. Mathematical techniques designed to analyze direction were used to find the dendritic field orientation of each cell. Statistical techniques designed for angular data were used to determine the relationship between dendritic field orientation and angular position on the retina (polar angle). Our results indicate that 88% of retinal ganglion cells have oriented dendritic fields and that dendritic field orientation is related systematically to retinal position. In all regions of retina more that 0.5 mm from the area centralis the dendritic fields of retinal ganglion cells are oriented radially, i.e., like the spokes of a wheel having the area centralis at its hub. This relationship was present in all animals and cell types studied and was strongest for cells located close to the horizontal meridian (visual streak) of the retina. Retinal ganglion cells appear to be sensitive to stimulus orientation because they have oriented dendritic fields.

Effects of visual deprivation upon the geniculocortical W-cell pathway in the cat: area 19 and its afferent input.

We studied the receptive field properties of 206 single units in area 19 of normal cats and 228 single units in area 19 of cats deprived of vision for 9-14 months by monocular lid suture. The ocular dominance of a sample of cells in area 17 of normal cats was studied for comparison. In some of these monocularly deprived animals, we also studied the sizes of relay cells in the parvocellular C laminae of the dorsal lateral geniculate nucleus labeled by electrophoretic injections of horseradish peroxidase into area 19. In area 19 of normal cats, the large majority of cells, regardless of their laminar location and the retinal eccentricity of their receptive fields, were binocular. Most responded equally well to the two eyes. In area 17, (see also Leventhal and Hirsch, '78, '80) but not in area 19, the cells which had the narrowest receptive fields tended to be activated unequally by the two eyes. In area 19 of monocularly deprived cats, virtually all cells (97%), regardless of their laminar location and receptive field eccentricity, responded only to stimulation of the normal eye. Thus, the effects of monocular deprivation upon area 19 are apparently more severe than those reported for area 17. In area 17 significant numbers of neurons in layer 4 can be activated by the deprived eye (Shatz and Stryker, '78). Within the limits of our technique, measurements of relay cells in the parvocellular C laminae labeled by injections into area 19 of deprived cats indicated that cell size in the deprived C laminae was unaffected by the deprivation. In contrast, cells in the deprived A laminae of these cats were severely shrunken. These findings suggest that the types of relay found in the parvocellular C laminae (referred to collectively as W-cells) are not affected by visual deprivation as severely as are the X- and Y-cells in the A laminae. Since laminar location and receptive field width are related to binocularity in area 17 but not in area 19 and the sizes of relay cells in the parvocellular C laminae (see also Hickey, '80) are not seriously affected by monocular deprivation, it is suggested that binocular interactions in area 19 are mainly determined by connections among cortical cells.

Relationships between ganglion cell dendritic structure and retinal topography in the cat.

The morphology of ganglion cell dendritic trees varies across the cat retina. Evidence is presented that the variation in two attributes of ganglion cell dendritic structure can be accounted for by specific aspects of the topography of the adult and developing retina. The first attribute considered was the displacement of the center of the dendritic field from the cell body in the plane of the retina. The results of this study provide evidence that most ganglion cell dendritic fields are displaced away from neighboring cells, i.e., down the retinal ganglion cell density gradient. Because of the systematic dendritic displacement locally, the centers of the dendritic fields are arranged in a more precise mosaic than are their cell bodies. The second attribute considered was the elongation and orientation of the dendritic fields. From approximately embryonic day 50 to postnatal day 10 the cat retina undergoes a process of maturation (reviewed by Rapaport and Stone: Neuroscience 11:289-301, '84) that begins at the area centralis and spreads over the retina in a horizontally elongated wave. We found that the elongation and orientation of retinal ganglion cell dendritic fields is significantly correlated with the shape of the wave of maturation. The orientation of a dendritic field is not predicted by the direction of its displacement nor is it directly related to the distribution of neighboring retinal ganglion cells. These results indicate that the displacement of a ganglion cell's dendritic field from its cell body results from mechanisms different from those responsible for the orientation of the dendritic field. Factors that may be responsible for these two attributes of ganglion cell dendritic morphology are discussed.

Retinal ganglion cells within the foveola of New World (Saimiri sciureus) and Old World (Macaca fascicularis) monkeys.

The morphology and distribution of retinal ganglion cells within the foveola of New World (Saimiri sciureus) and Old World (Macaca fascicularis) monkeys labeled as a result of horseradish peroxidase injections into the dorsal lateral geniculate nucleus were studied. The results indicate that monkey's foveola normally contains significant numbers of retinal ganglion cells. Most of these project ipsilaterally. Cells within the foveola are larger than other cells in monkey central retina; their dendritic fields are up to 50 times larger in area than those of cells in the foveal slope. The dendritic fields of the ganglion cells within the foveola cover at least 70-100% of its area. Among ganglion cells within the foveola (as in most ganglion cells), there was a strong tendency for the axon and dendritic tree to arise from opposite poles of the soma. The axon-dendrite axes of ganglion cells within the foveola did not show a consistent pattern. In contrast, the axes of ganglion cells in the transition zone between the foveola and the foveal slope were directed tangentially to the circumference of the fovea. The dendritic coverage of the foveola by retinal ganglion cells suggests functional significance and provides a possible neural basis for 2-3 degrees of bilateral representation of the fovea within the central visual pathways. Alternatively, or in addition, these cells may be "remnants of foveation" and provide insight into the developmental processes that mediate the development of the fovea.

The afferent ganglion cells and cortical projections of the retinal recipient zone (RRZ) of the cat's pulvinar complex'.

A retino-pulvinar projection in the cat was confirmed using anterograde (autoradiography) and retrograde (horseradish peroxidase (HRP)) tracing techniques. The part of the "pulvinar complex" receiving retinal afferents is referred to as the retinal recipient zone (RRZ). The cortical projections of the RRZ were studied by injecting HRP into different cortical areas. The retrograde labeling of the cell bodies and dendritic fields of the retinal ganglion cells projecting to the RRZ was accomplished by injecting HRP electrophoretically into the RRZ. Our results indicate that the RRZ projects to areas 19 and the lateral suprasylvian area (LS) but not to areas 17 or 18. Virtually all RRZ cells, including those that project to the cortex, are small (10-20 micron in diameter); they are the same size as the relay cells of the parvocellular C laminae of the lateral geniculate nuclear complex (LGNd) that project to areas 19 and LS. The majority of the ganglion cells projecting to the RRZ had medium-sized somas (15-25 micron in diameter), large (up to 800 micron in diameter), diffuse dendritic fields with a characteristic morphology, and appeared different from the alpha, beta, gama, and delta cells of Boycott and Wässle ('74). These cells provide evidence for another morphological class of ganglion cells, termed epsilon cells. Our results suggest that the RRZ relays the activity of specific types of retinal ganglion cells to extrastriate visual cortex and, thus, functions in parallel with the different subdivisions of the LGNd.

Central projections of cat retinal ganglion cells.

The central projections of different groups of cat retinal ganglion cells were studied following small iontophoretic injections of horseradish peroxidase (HRP) into physiologically characterized sites. Analysis was restricted to labeled cells in the upper periphery of the nasal retina, contralateral to the injection site. Injections were made to the A lamina and C lamina of the dorsal lateral geniculate nucleus (LGNd-A,C), the geniculate wing (LGNd-W), the ventral lateral geniculate nucleus (LGNv), the pretectum (PT), and the superior colliculus (SC). The dendritic fields of alpha, beta, and epsilon cells were well labeled by the procedures we employed. A group, termed "g1," had somal sizes within the range of the smaller beta and epsilon cells, but dendritic morphologies distinct from either class. The g1 group may consist of a number of types, but our material provided no basis for further distinguishing them. Many cells were observed that had smaller somas; all had thin axons, and few had dendritic fields that labeled to any significant extent. We were not able to further distinguish these cells, and refer to this group, which may include a number of types, as "g2" cells. From the peripheral nasal retina, alpha cells project to LGNd-A, LGNd-C, PT, and SC. Beta cells project to LGNd-A, LGNd-C, and PT. Epsilon and g1 cells project to the LGNd-C, LGNd-W, LGNv, PT, and SC. We determined the total spatial density of cells in the region of the retina analyzed, using a Nissl-stained preparation. We then estimated the relative fraction of cells in each of the above groupings by injecting HRP throughout a cross section of the optic tract. Multiplying this relative fraction by the total spatial density gave an estimate of the spatial density of each of these groupings. From the spatial density of cells labeled from the injection site, we were able to estimate the fraction of cells of each retinal grouping that project to each of the zones investigated. By these calculations, almost all alpha cells from the upper nasal retina project to LGNd-A and LGNd-C; most project to SC, and about a third to PT. Beta cells, by contrast, project almost exclusively to LGNd-A, with about 10% going to LGNd-C, and about 1% to the PT. The great majority of epsilon cells, if not all, project to LGNd-W, and up to half of this population also project to the other zones noted above.(ABSTRACT TRUNCATED AT 400 WORDS)

Relationship between preferred orientation and receptive field position of neurons in extrastriate cortex (area 19) in the cat.

Orientation sensitivity is a characteristic of most retinal ganglion cells (Levick and Thibos, '82), most relay cells in the dorsal lateral geniculate nucleus (Vidyasagar and Urbas, '82), and most neurons in the visual cortex (Hubel and Wiesel, '62) in the cat. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis most retinal ganglion cells respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick and Thibos, '82). This relationship is strongest along the horizontal meridian (the visual streak) and appears to reflect the innate, radial orientation of retinal ganglion cell dendritic fields (Leventhal and Schall, '83). A relationship between preferred orientation and polar angle also exists in cat striate cortex; outside of the area centralis representation most cells respond best to lines oriented radially. This relationship is strongest for S-type cells, the most orientation-selective cells, and cells in regions representing the horizontal meridian (Leventhal, '83). To determine if similar relationships exist in cat extrastriate cortex, the preferred orientations and receptive field positions of 226 neurons in area 19 were studied. We find that, as in area 17, most area 19 cells outside of the representation of the area centralis respond best to lines oriented radially; this relationship is strongest for the cells having the narrowest receptive fields and in regions subserving the horizontal meridian. Unlike in striate cortex, in area 19 the relationship between preferred orientation and polar angle is not dependent upon cell type (S or C) or to the degree of orientation sensitivity exhibited. Also, in area 19, but not in area 17, the relationship between preferred orientation and polar angle fails for the cells having the widest receptive fields.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology, central projections, and dendritic field orientation of retinal ganglion cells in the ferret.

Retinal ganglion cells were studied in pigmented ferrets that received small electrophoretic injections of horseradish peroxidase (HRP) into the dorsal lateral geniculate nucleus (LGNd) or optic tract. Ferret retina contains a number of types of retinal ganglion cells of which the relative cell body sizes, dendritic field structures, and central projections correspond closely to those of retinal ganglion cell types in the cat. Ferret retina contains about the same proportion of alphalike cells, a lower proportion of betalike cells, and thus a high proportion of other types of ganglion cells than cat retina. Ferret retina has a visual streak and somewhat weaker area centralis than cat retina. Changes in ganglion cell morphology associated with eccentricity are less pronounced in the ferret than in the cat. The adult ferret retina is about 12.5 mm in diameter, and the nasotemporal division is about 2.7 mm from the temporal margin. Interestingly, virtually all alpha cells in the pigmented ferrets studied projected contralaterally. Studies of infant ferrets indicate that 4 days after birth (P4) the area of ferret retina is 25% that of the adult. The neonatal ferret retina contains numerous small, densely packed cells in the presumptive ganglion cell layer. At P4 these cells appear to be uniformly distributed across the retina. The area centralis and visual streak are not obvious as late as 8 days after birth.

Ganglion cell dendritic structure and retinal topography in the rat.

The dendritic field size, the distribution of the dendrites relative to the cell body, and the overall shape of the dendritic field of type I ganglion cells in the rat retina were analyzed. These features of neuronal structure were related to the topography of the rat retina. As in the cat, the cell bodies of type I ganglion cells are arranged in a nonrandom mosaic. Previous work has demonstrated that the density of type I cells in the rat retina does not covary with the density of all ganglion cells. Type I dendritic field size varies over the retina; the increase in dendritic field size is accounted for better by the decrease in type I density than by the decrease in overall ganglion cell density. The center of the dendritic field of most type I cells is displaced in the plane of the retina from the cell body. Unlike in carnivore retina (Schall and Leventhal: J. Comp. Neurol. 257:149-159, '87), the dendritic fields in the rat are not displaced down the ganglion cell density gradient. Rather, there is a tendency for the dendritic trees, especially in temporal retina, to be displaced toward dorsal retina. Most of the dendritic fields are elongated, but the degree of elongation is less than that observed in carnivore or primate retina. Unlike in carnivore and primate retina (Leventhal and Schall: J. Comp. Neurol. 220:465-475, '83; Schall et al.: Brain Res. 368:18-23, '86), there is no relationship between dendritic tree orientation and position relative to any point on the retina in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Extrinsic determinants of retinal ganglion cell development in primates.

As in all mammals studied to date, primate retina contains morphologically distinct classes of retinal ganglion cells (Polyak: The Retina. Chicago: University of Chicago Press, '41; Boycott and Dowling: Philos. Trans. R. Soc. Lond. [Biol.] 225:109-184, '69; Leventhal et al.: Science 213:1139-1142, '81; Perry et al.: Neuroscience 12:1101-1123, '84; Rodieck et al.: J. Comp. Neurol. 233:115-132, '85; Rodieck: In H.D. Steklis and J. Erwin (eds): Comparative Primate Biology, Volume 4: Neurosciences. New York: Alan R. Liss, Inc., pp. 203-278, '88). We have now studied the morphologies, central projections, and retinal distributions of the major morphological classes of ganglion cells in the normal adult monkey, the newborn monkey, and the adult monkey in which restricted regions of retina were depleted of ganglion cells at birth as a result of small lesions made around the perimeter of the optic disc. Both old-world (Macaca fascicularis) and new-world (Saimiri sciureus) monkeys were studied. Our results indicate that, at birth, the major morphological classes of monkey retinal ganglion cells are recognizable; cells in central regions are close to adult size whereas cells in peripheral regions are much smaller than in the adult. As in the adult (Stone et al.: J. Comp. Neurol. 150:333-348, '73), in newborn monkeys there is a very sharp division between ipsilaterally and contralaterally projecting retinal ganglion cells (nasotemporal division). Consistent with earlier work (Hendrickson and Kupfer: Invest. Ophthalmol. 15:746-756, '76) we find that the foveal pit in the neonate is immature and contains many more ganglion cells than in the adult. In the adult monkey in which the density of retinal ganglion cells in the central retina was reduced experimentally at birth, the fovea appeared immature, and an abnormally large number of retinal ganglion cells were distributed throughout the foveal pit. The cell bodies and dendritic fields of ganglion cells that developed within cell-poor regions of the central retina were nearly ten times larger than normal. In peripheral regions the effects were smaller. The dendrites of the abnormally toward the foveal pit. They did not extend preferentially into the cell-poor region as do the abnormally large cells on the borders of experimentally induced cell-poor regions of cat central retina (Leventhal et al.: J. Neurosci. 8:1485-1499, '88) or, as we found here, in paracentral regions of primate retina.(ABSTRACT TRUNCATED AT 400 WORDS)

Abnormal retinotopic organization of the dorsal lateral geniculate nucleus of the tyrosinase-negative albino cat.

Visual defects associated with hypopigmentation have been studied extensively in Siamese and albino cats. Previous research on tyrosinase-negative albino cats has shown that (1) approximately 95% of all nasal and temporal retinal fibers cross at the optic chiasm, and (2) ocular dominance columns normally found in cortex are replaced with hemiretinal domains. In this study, we compared the retinotopic organization of the dorsal lateral geniculate nucleus (LGNd) and visual cortex in albino cats. Extracellular recordings were conducted in the LGNd, area 17, and area 18 of six albino cats. Receptive fields (RFs) were plotted for all sites. We find that, as in albino visual cortex, the albino LGNd contains (1) normal cells with RFs in the visual hemifield contralateral to the recording site (RFc), (2) abnormal cells with RFs in the ipsilateral hemifield (RFi), (3) abnormal cells with dual, mirror-symmetric RFs, one in each hemifield (RFd), and (4) abnormal cells with broad RFs that span the vertical meridian (RFb). Our data indicate that lamina A and lamina A1 consist predominantly of normal RFc and abnormal RFi cells, respectively. The C laminae contain a mixture of RFc, RFi, RFd, and RFb cells. The interlaminar zones contained RFd cells, RFb cells, or both. Thus, the albino LGNd is arranged into hemiretinal and not ocular dominance laminae. Finally, the percentage of normal cells is significantly larger in area 17 (84%) and area 18 (70%) than in the LGNd (46%), suggesting a suppression of abnormal activity in albino cat cortex, which could underlie the existing competence of visual function in albinos.