Human, macaque monkey, and rat retinas were immunostained with a polyclonal antibody preparation against purified recoverin, a 23-kD calcium-binding protein isolated from bovine retina that localizes to rods and cones (Dizhoor et al., 1991). In addition to immunoreactive photoreceptors, we have identified subpopulations of recoverin-positive bipolar cells in all three species. Results from immunostaining with progressive dilutions of anti-recoverin and preadsorption of the antibody with a dilution series of purified recoverin showed that photoreceptors and bipolar cells had similar affinities for the antibody and suggested that the molecule recognized by the antibody in both cell types is recoverin. Immunoreactivity for recoverin and protein kinase C, a selective marker for all rod bipolar cells, was found in separate bipolar cell populations. Recoverin immunoreactivity is therefore a characteristic of certain cone bipolar cell types.

In rat retina, anti-recoverin labeled two morphologically distinct subpopulations of cone bipolar cells whose axonal arbors stratified at different depths in the inner plexiform layer (IPL). The bipolar cells labeled with anti-recoverin did not correspond to those that were reactive for calbindin, another cone bipolar cell marker.

Human and monkey retinas also had two populations of cone bipolar cells that were recoverin-positive. One population showed a distinct pattern of narrow bistratification at the outer border of the IPL and a regular mosaic arrangement of its axonal arbors, suggesting that the entire population of a single cone bipolar type was labeled. Cell density, dendritic morphology, and axonal-field size and stratification indicate that anti-recoverin selectively stains the flat midget (presumed OFF-center) cone bipolar cell type observed previously in Golgi preparations. By contrast the second bipolar cell population had axonal stratification in the inner half of the IPL and showed an unusual but consistent morphology and spatial distribution. Individual cells were intensely stained but were present at an extremely low density (~2−5 cells/mm2). These cells had multibranched dendritic trees characteristic of the diffuse bipolar cell class, but very small axonal fields in the size range of the midget bipolar class. Neither of the two recoverin-positive bipolar cell types in monkey was labeled with anti-calbindin or anti-cholecystokinin. An antibody preparation against bovine pineal hydroxyindole-O-methyltransferase (HIOMT) labeled photoreceptors and bipolar cells that closely resembled the recoverin-positive bipolar cells in human and rat retinas. Preadsorption of this antibody preparation with purified recoverin abolished immunostaining of the bipolar cells, suggesting that the anti-HIOMT preparation contains antibodies against recoverin, which is known to be present in the bovine pineal gland.

Two dots may be aligned vertically with a precision much higher than that expected from two-point resolution provided they are separated by a visual angle of 3–5 min of arc. This precision suffers when the two dots are not exposed synchronously. Neither onset nor offset asynchronies can be tolerated; exposure differences of the two components of the vernier task as low as 30 ms can lead to a reduction in performance when the total exposure is below 90 ms. This effect cannot be compensated for by synchronizing the onset of one stimulus component with the offset of the other, even when the two are of opposite contrast. The data suggest that vernier acuity may be subserved by a dynamical linking of cortical excitation generated by the synchronous arrival of signals within a range of locations in the cortex whose spatial separation is critical for optimal hyperacuity performance. The evidence presented in this paper must be taken into account when a physiological substrate for hyperacuity is considered.

The responses of single cells to luminance, color and computer-generated spots, bars, kinematograms, and motion-in-depth stimuli were studied in the nucleus rotundus of pigeons. Systematic electrode penetrations revealed that there are several functionally distinct subdivisions within rotundus where six classes of visual-selective cells cluster. Cells in the dorsal-posterior zone of the nucleus respond selectively to motion in depth (i.e. an expanding or contracting figure in the visual field). Most cells recorded from the dorsal-anterior region responded selectively to the color of the stimulus. The firing rate of the cells in the anterior-central zone, however, is dramatically modulated by changing the level of illumination over the whole visual field. Cells in the ventral subdivision strongly respond to moving occlusion edges and very small moving objects, with either excitatory or inhibitory responses. These results indicate that visual information processing of color, ambient illumination, and motion in depth are segregated into different subdivisions at the level of nucleus rotundus in the avian brain.

We have studied the organization of receptive fields of ganglion cells in the isolated mouse retina and have shown that the organization is similar to that of the cat. Based upon responses to circular and annular stimuli, most ganglion cells (90%; N = 83) had receptive fields with concentric center-surround organization, either ON or OFF center. The plot of response amplitude vs. stimulus area for these cells increased to a maximum (corresponding to a diameter of 10.0 ± 2.8 deg S.E.M.; N = 13) and then decreased for larger stimuli, demonstrating the presence of an antagonistic surround. The dark-adapted sensitivity (205 ± 43.8 impulses quantum−1 rod−1; mean ± S.E.M.) did not differ from that measured for the intact preparation. We found a subset of OFF-center cells for which the dark discharge was very regular (mean coefficient of variation = 0.30). Using sinusoidal grating stimuli, we classified ganglion cells as X-like (87%) and Y-like (13%) based on spatial summation properties and the presence of subunit activity in the receptive-field center. We found no difference in the spatial-frequency preference between X-like and Y-like cells in the central retina (high cutoff frequency, 0.20 ± 0.014 cycle/deg, mean ± S.E.M.), in contrast to the marked difference between X cells and Y cells in the cat. Thus, ganglion cell receptive fields in the mouse retina resemble those of the cat, although the spatial characteristics of the receptive fields in the central retina are more homogeneous. This homogeneity would simplify the comparison of retinas from normal and mutant strains of the mouse.

Cytochrome-oxidase (CO) histochemistry has revealed important functional subdivisions, modules, and processing streams in the macaque visual cortex. The present study is aimed at analyzing the development and characteristics of CO patterns in the human visual cortex by means of histochemistry and immunohistochemistry. At 26 weeks of gestation, both the ventricular and subventricular zones had low levels of CO, while the cortical plate had moderate levels of CO. At birth, supragranular CO-rich zones (puffs) were not clearly organized, indicating that the development of puffs in the neonatal striate cortex lags behind that of the macaque monkey, whose puffs appear weeks before birth. Puffs were more clearly discernible in human cortex at postnatal day 24, and became well organized by the fourth postnatal month. Layer IVcα in the neonate exhibited a higher level of activity and amount of CO than the central portion of IVcβ, which contained a dense aggregate of small neurons. The base of IVcβ, however, was often as CO reactive as IVcα. In contrast, the majority of specimens available to us from the fourth postnatal month and from adults with no known neurological diseases had significantly greater CO reactivity in layer IVcβ than in IVcaβ. Layer VI was moderately reactive for CO throughout development. In V2, stripes with globular zones of high CO activity were sporadically present at birth, suggesting that their development may parallel or precede that of puffs in VI. These stripes with CO-rich globular zones became more prominent in the adult and radiated orthogonally from the V1/V2 border. They were not, however, clearly organized into alternating thick and thin stripes as they are in the squirrel monkey. Visual cortical areas beyond V2 exhibited high CO activity mainly in layers III and IV and moderate levels in VI, suggesting that sites associated with cortico-cortical pathways may be metabolically most active.

To investigate the subcortical connections of the object vision and spatial vision cortical processing pathways, we injected the inferior temporal and posterior parietal cortex of six Rhesus monkeys with retrograde or anterograde tracers. The temporal injections included area TE on the lateral surface of the hemisphere and adjacent portions of area TEO. The parietal injections covered the posterior bank of the intraparietal sulcus, including areas VIP and LIP. Our results indicate that several structures project to both the temporal and parietal cortex, including the medial and lateral pulvinar, claustrum, and nucleus basalis. However, the cells in both the pulvinar and claustrum that project to the two systems are mainly located in different parts of those structures, as are the terminals which arise from the temporal and parietal cortex. Likewise, the projections from the temporal and parietal cortex to the caudate nucleus and putamen are largely segregated. Finally, we found projections to the pons and superior colliculus from parietal but not temporal cortex, whereas we found the lateral basal and medial basal nuclei of the amygdala to be reciprocally connected with temporal but not parietal cortex. Thus, the results show that, like the cortical connections of the two visual processing systems, the subcortical connections are remarkably segregated.

In previous experiments we established that a light flash reduced cGMP levels of toad rod outer segments within the transduction time interval, but that recovery of the dark level of cGMP occurred more slowly than reported electrophysiological recovery of membrane potential. We now report that a second light flash accelerates the recovery rate of total cGMP following an initial flash, but that this acceleration is blocked in a medium which is both sodium and calcium deficient. We also noted that calcium deficiency only elevated cGMP levels when sodium was present. For other experiments, we recorded ERG or aspartate isolated PIII responses from eyecups or retinas mounted on our quick-freeze apparatus, the light stimuli originating from the double light-bench of the latter. Whereas background illumination depressed cGMP, no detectable further cGMP loss accompanied the electrical response to a flash superimposed on the background.

The effects of small changes in the calcium and sodium concentrations and in the pH of superfusion medium on the membrane potential and light-evoked responses of cone horizontal cells in the goldfish retina were examined. Conventional intracellular recording, a bicarbonate-based superfusion medium, and a specially designed superfusion apparatus that reduced pressure wave disturbances were used. An increase in the extracellular calcium concentration, [Ca2+]∘ from control levels (0.1 mM) to 1.0 mM hyperpolarized cone horizontal cells and reduced the magnitude of their light responses at all stimulus intensities. Addition of 20 mM NaCl to the 1.0 mM Ca2+ Ringer’s solution reversed the hyperpolarizing effect of the 1.0 mM Ca2+ but addition of 20 mM choline, a monovalent cation that does not pass through cyclic GMP-activated channels, did not. Reduction of the superfusate pH from 7.6 to 7.2 by switching from a Ringer’s solution gassed with 3% CO2 to one gassed with 10% CO2 hyperpolarized horizontal cells and reduced the magnitude of their light responses at all stimulus intensities for both 0.1 and 1.0 mM Ca,2+ Ringer’s solutions. An increase in pH to 8.2 by gassing the superfusate with 1% CO2 slightly depolarized the cells in 0.1 mM Ca2+ Ringer’s solution but slightly hyperpolarized the cells in the 1.0 mM Ca2+ Ringer’s solution. Following pharmacological isolation of the horizontal cells from synaptic input with high doses of glutamate (4–5 mM) and/or Co2+ (4 mM) treatment, no effect on horizontal cell membrane potential due to changes in pH or [Ca2+]∘ was observed. These findings are discussed with respect to the cellular mechanisms and sites of action in the outer retina that are affected by changes in pH∘ and [Ca2+]∘.

Extracellular recordings from single neurons have been made from presumed area 21a of the cerebral cortex of the cat, anesthetized with N2O/O2/sodium pentobarbitone mixture. Area 21a contains mainly a representation of a central horizontal strip of contralateral visual field about 5 deg above and below the horizontal meridian.

Excitatory discharge fields of area 21a neurons were substantially (or slightly but significantly) larger than those of neurons at corresponding eccentricities in areas 17, 19, or 18, respectively. About 95% of area 21a neurons could be activated through either eye and the input from the ipsilateral eye was commonly dominant. Over 90% and less than 10% of neurons had, respectively, C-type and S-type receptive-field organization. Virtually all neurons were orientation-selective and the mean width at half-height of the orientation tuning curves at 52.9 deg was not significantly different from that of neurons in areas 17 and 18. About 30% of area 21a neurons had preferred orientations within 15 deg of the vertical.

The mean direction-selectivity index (32.8%) of area 21a neurons was substantially lower than the indices for neurons in areas 17 or 18. Only a few neurons exhibited moderately strong end-zone inhibition. Area 21a neurons responded poorly to fast-moving stimuli and the mean preferred velocity at about 12.5 deg/s was not significantly different from that for area 17 neurons.

Selective pressure block of Y fibers in contralateral optic nerve resulted in a small but significant reduction in the preferred velocities of neurons activated via the Y-blocked eye. By contrast, removal of the Y input did not produce significant changes in the spatial organization of receptive fields (S or C type), the size of the discharge fields, the width of orientation tuning curves, or direction-selectivity indices.

Our results are consistent with the idea that area 21a receives its principal excitatory input from area 17 and is involved mainly in form rather than motion analysis.

The objective of this study was to determine when the retina, lateral geniculate nucleus (LGN), and striate cortex first send out axons, and first connect with each other, during embryonic development in the ferret. Specifically, we were interested in the timing relationship between axon outgrowth and known temporal patterns of neurogenesis in the LGN and striate cortex. Ferrets (Mustela putorius furo) were selected for study because of their immature developmental state in late gestation and relatively large litters.

We examined axon outgrowth from the retina, and anlagen of presumptive LGN and striate cortex between embryonic day 21–30 (E21–E30) using in situ inoculations of two fluorescent lipophilic dyes, Dil and DiA. Dil inoculations were made into the cortex and contralateral thalamus, and DiA inoculations were made into the contralateral eye. Retinal axon termination zones in the diencephalon following the DiA inoculations were used to validate the location of the LGN.

Visual cortex and LGN neurogenesis begins at E20 in ferrets. No axon outgrowth could be documented from retina or anlagen of striate cortex and LGN until E24. At E24 some retinal axons reach and cross the chiasm, cortical axons extend some distance within the cortical radiations, and thalamic axons are within the internal capsule. Retinogeniculate, geniculocortical, and corticogeniculate axons extend to their target structures by E27, as evidenced by retrograde labeling in cells of origin.

These data suggest that in the ferret retina, and developing LGN and striate cortex, (1) axon outgrowth from each visual area begins within 24-h of each other, after neurogenesis has begun at the source but before it is complete in the target; (2) axons may be generated before parent cell bodies have completed migration; and (3) arriving axons are in a position to influence target structures almost from their inception.

Lateral suprasylvian visual cortex in the cat has been studied extensively, but its retinotopic organization remains controversial. Although some investigators have divided this region into many distinct areas, others have argued for a simpler organization. A clear understanding of the region’s retinotopic organization is important in order to define distinct areas that are likely to subserve unique visual functions. We therefore reexamined the map of the lower visual field in the striate-recipient region of lateral suprasylvian cortex, a region we refer to as the lateral suprasylvian area, LS.

A dual mapping approach was used. First, receptive fields were plotted at numerous locations along closely spaced electrode penetrations; second, different anterograde tracers were injected at retinotopically identified sites in area 17, yielding patches of label in LS. To visualize the resulting data, suprasylvian cortex was flattened with the aid of a computer.

Global features of the map reported in many earlier studies were confirmed. Central visual field was represented posteriorly, and elevations generally shifted downward as one moved anteriorly. Often (though not always) there was a progression from peripheral locations towards the vertical meridian as the electrode moved down the medial suprasylvian bank.

The map had some remarkable characteristics not previously reported in any map in the cat. The vertical meridian’s representation was split into two pieces, separated by a gap, and both pieces were partially internalized within the map. Horizontal meridian occupied the gap. The area centralis usually had a dual representation along the posterior boundary of the lower field representation, and other fragments of visual field were duplicated as well. Finally, magnification appeared to change abruptly and unexpectedly, so that compressed regions of representation adjoined expanded regions. Despite its complexity, we found the map to be more orderly than previously thought. There was no clearcut retinotopic basis on which to subdivide LS’s lower field representation into distinct areas.

The classically defined receptive fields of V4 cells are confined almost entirely to the contralateral visual field. However, these receptive fields are often surrounded by large, silent suppressive regions, and stimulating the surrounds can cause a complete suppression of response to a simultaneously presented stimulus within the receptive field. We investigated whether the suppressive surrounds might extend across the midline into the ipsilateral visual field and, if so, whether the surrounds were dependent on the corpus callosum, which has a widespread distribution in V4. We found that the surrounds of more than half of the cells tested in the central visual field representation of V4 crossed into the ipsilateral visual field, with some extending up to at least 16 deg from the vertical meridian. Much of this suppression from the ipsilateral field was mediated by the corpus callosum, as section of the callosum dramatically reduced both the strength and extent of the surrounds. There remained, however, some residual suppression that was not further reduced by addition of an anterior commissure lesion. Because the residual ipsilateral suppression was similar in magnitude and extent to that found following section of the optic tract contralateral to the V4 recording, we concluded that it was retinal in origin. Using the same techniques employed in V4, we also mapped the ipsilateral extent of surrounds in the foveal representation of VI in an intact monkey. Results were very similar to those in V4 following commissural or contralateral tract sections. The findings suggest that V4 is a central site for long-range interactions both within and across the two visual hemifields. Taken with previous work, the results are consistent with the notion that the large suppressive surrounds of V4 neurons contribute to the neural mechanisms of color constancy and figure-ground separation.

Electroretinogram (ERG) flicker photometry was used to examine the photopigment complements of representatives of four genera of Canid: domestic dog (Canis familiaris), Island gray fox (Urocyon littoralis), red fox (Vulpes vulpes), and Arctic fox (Alopex lagopus). These four genera share a common cone pigment complement; each has one cone pigment with peak sensitivity of about 555 nm and a second cone pigment with peak at 430–435 nm. These pigment measurements accord well with the conclusions of an earlier investigation of color vision in the dog, and this fact allows some predictions about color vision in the wild canids. An additional set of measurements place the peak of the dog rod pigment at about 508 nm.

The effects of vasoactive intestinal peptide (VIP) on the extracellularly recorded activity of ganglion cells were studied in superfused rabbit retinas. VIP, applied to the bathing solution, significantly increased the maintained activity of both OFF-center and ON-center brisk ganglion cells. The transient, excitatory responses of these cells to flashes of light (spots or annuli centered over the receptive field) were either unaffected or moderately reduced. VIP did not affect the responses of most ON/OFF directionally selective ganglion cells to a moving light stimulus. Furthermore, maintained activity of most of these cells remained absent.

Effects of VIP on the light responses of ganglion cells were pronounced in retinas that were bathed with the dopamine D1 antagonist (+)-SCH 23390. For OFF-center brisk ganglion cells, VIP brought out both the center and surround excitatory responses that were selectively reduced by (+)-SCH 23390. Similarly, VIP brought out the leading edge responses that were reduced by (+)-SCH 23390 in ON/OFF directionally selective ganglion cells to a moving light stimulus. VIP did not however reverse the effects of (+)-SCH 23390 on ON-center brisk ganglion cells. It is argued that VIP counteracts the effects of (+)-SCH 23390 on OFF-center brisk ganglion cells and ON/OFF directionally selective ganglion cells by stimulating adenylate cyclase activity in dopamine-receptive cells of the retina.

Hartveit, E. & Heggelund, P. (1992). The effect of contrast on the visual response of lagged and nonlagged cells in the cat lateral geniculate nucleus. Visual Neuroscience9, 515–525.