A four-surface schematic eye of macaque monkey obtained by an optical method.

Schematic eyes for four Macaca fascicularis monkeys were constructed from measurements of the positions and curvatures of the anterior and posterior surfaces of the cornea and lens. All of these measurements were obtained from Scheimpflug photography through the use of a ray-tracing analysis. Some of these measurements were also checked (and confirmed) by keratometry and ultrasound. Gaussian lens equations were applied to the measured dimensions of each individual eye in order to construct schematic eyes. The mean total power predicted by the schematic eyes agreed closely with independent measurements based on retinoscopy and ultrasound results, 74.2 +/- 1.3 (SEM) vs 74.7 +/- 0.3 (SEM) diopters. The predicted magnification of 202 microns/deg in one eye was confirmed by direct measurement of 205 microns/deg for a foveal laser lesion. The mean foveal retinal magnification calculated for our eight schematic eyes was 211 +/- (SEM) microns/deg, slightly less than the value obtained by application of the method of Rolls and Cowey [Experimental Brain Research, 10, 298-310 (1970)] to our eight eyes but just 4% more than the value obtained by application of the method of Perry and Cowey [Vision Research, 12, 1795-1810 (1985)].

M and L cones in macaque fovea connect to midget ganglion cells by different numbers of excitatory synapses.

Visual acuity depends on the fine-grained neural image set by the foveal cone mosaic. To preserve this spatial detail, cones transmit through non-divergent pathways: cone-->midget bipolar cell-->midget ganglion cell. Adequate gain must be established along each pathway; crosstalk and sources of variation between pathways must be minimized. These requirements raise fundamental questions regarding the synaptic connections: (1) how many synapses from bipolar to ganglion cell transmit a cone signal and with what degree of crosstalk between adjacent pathways; (2) how accurately these connections are reproduced across the mosaic; and (3) whether the midget circuits for middle (M) and long (L) wavelength sensitive cones are the same. We report here that the midget ganglion cell collects without crosstalk either 28 +/- 4 or 47 +/- 3 midget bipolar synapses. Two cone types are defined by this difference; being about equal in number and distributing randomly in small clusters of like type, they are probably M and L.

A role for the corpus callosum in visual area V4 of the macaque.

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 V1 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.

Gap junctions between the pedicles of macaque foveal cones.

Cone terminals ("pedicles") in the fovea of macaque retina were studied in electron micrographs of serial sections. Pedicles were sheathed in glia except for small (0.2 microns 2) fenestrations, 4.8 +/- 1.7 per pedicle. At each fenestration the membranes of adjacent pedicles were contiguous and marked by an adherent junction, which in turn was invariably associated with gap junctions. There were 3.2 +/- 1.4 gap junctions per adherent junction and thus, about fifteen gap junctions per pedicle. The gap junctions were small, 1.6 x 10(-3) +/- 1.8 x 10(-3) microns 2 (mean +/- SD) and were formed indiscriminately with all neighboring pedicles. An upper bound was estimated of 170 connexons per pedicle and thus a coupling conductance of 1.7 x 10(4) pS. Available psychophysical data suggest that the junctions are uncoupled at high luminance. They may couple at lower luminance where spatial averaging would improve contrast sensitivity without cost to spatial acuity.

Detection and abundance of mRNA and protein encoded by transposable element activator (Ac) in maize.

The 3.5 kb long mRNA of the maize transposable element Ac contains an open reading frame (ORFa) which encodes a polypeptide of 807 amino acids, the putative transposase of Ac. The Ac mRNA is a rare transcript: we now estimate the fraction of Ac mRNA in wx-m7::Ac seedlings to be 2-13 x 10(-5) of the polyA RNA. Assuming that maize cells contain similar amounts of polyA RNA as another monocot (0.16 pg/cell), this is equivalent to 1.5-10 transcripts in each cell. A protein with an apparent molecular weight of 112 kDa is detected, by five antisera directed against different segments of ORFa, exclusively in nuclear extracts from Ac-containing maize. This protein is most likely the full-length Ac ORFa protein. We estimate its concentration to be in the range of 3 x 10(-7) of the nuclear proteins, or about 1000 molecules per triploid endosperm cell containing one Ac element.

Spectral properties of V4 neurons in the macaque.

Spectral properties of 129 cells in the V4 area of 5 macaque monkeys were studied quantitatively with narrow-band and broad-band colored lights. The large majority of cells exhibited some degree of wavelength sensitivity within their receptive fields. The half-bandwidth of the primary peak in the spectral-response curve was less than 50 nm for 72% of the cells; the mean half-bandwidth of these cells, 27 nm, is similar to that found for color-opponent ganglion cells and cells in the parvocellular dorsal lateral geniculate nucleus (dLGN). Contrast-response functions indicated that the narrow spectral tuning of these cells derived from cone opponent interactions. From comparison of receptive-field sizes, we suggest that a typical V4 neuron sums inputs that ultimately derive from several thousand ganglion or parvocellular dLGN cells. In spite of their wavelength sensitivity, most V4 cells had properties that would not fit some simple criteria for classification as "color selective." First, few cells showed overt signs of color opponency, namely, on-inhibition or off-excitation to spectrally opponent wavelengths. Second, about 30% of the cells in V4 had spectral-response curves with 2 peaks. (The wavelength distribution of these second peaks was almost identical to that of primary peaks, and combinations of peak wavelengths were fairly random.) Third, most cells responded to white light; overall, the response to white light was about 60% of that to the best narrow-band or broad-band colored light. Similarly, most V4 cells gave at least a small response to all or nearly all of the different broad-band colored lights we presented. Therefore, a given V4 cell is very likely to respond to most of the colored or white surfaces in natural scenes. These combinations of response properties probably explain the widely divergent percentages of "color" cells reported in previous studies of V4. The most unusual spectral property we found in V4 was a large, spectrally sensitive surround outside the "classical receptive field" of most cells. Although stimulation of the surround by itself did not cause any response, surround stimulation could completely suppress the response to even the optimally colored stimulus in the receptive field. In general, the optimal wavelengths for receptive-field excitation and surround suppression were the same or nearly so. Thus, "color contrast" may be computed in V4. In some cases, contrasting wavelengths in the surround caused moderate enhancement of response to a receptive-field stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)

Anatomy of macaque fovea and spatial densities of neurons in foveal representation.

Fine visual sampling in the macaque depends on the high density of cone outer and inner segments in the fovea. Cone pedicles, at the opposite, presynaptic end of the cone, are absent from the center of the fovea. Both ends of the cones, inner segments and pedicles, are closely packed within their respective monolayers, but the spatial density of foveal pedicles is lower because foveal pedicles are wider than inner segments. Because there is one pedicle for every inner segment, and because pedicles are wider than inner segments, increase in eccentricity finds increasing lateral displacement of the cone's pedicle from its inner segment. Further increase of eccentricity finds inner segment density falling below pedicle density, and so this lateral displacement declines. By 2-3 mm from the center, inner segments catch up with pedicles. Additional lateral displacements, of bipolar cells from pedicles and ganglion from bipolar cells, are largest for central-most elements and fall steeply with eccentricity. By taking into account all of these lateral displacements, the eccentricity of the cone inner segment(s) associated with a ganglion cell was determined, as was the area of inner segments represented by a unit area in the ganglion cell layer. Then raw ganglion cell densities were transformed to densities comparable to densities of inner segments and of cells in dorsal lateral geniculate nucleus. On average there appears to be close to 2 ganglion cells for each cone in the central fovea out to about 2.5 degrees. Thus, the density of foveal ganglion cells is sufficient to allow each red and each green cone to connect to 2 midget ganglion cells, and each blue cone to connect to 1 ganglion cell. Furthermore, there appears to be a single dorsal lateral geniculate cell for each ganglion cell.

Mapping of retinal and geniculate neurons onto striate cortex of macaque.

A unity ratio between geniculate and ganglion cells can be shown in the macaque visual system. Comparison of the densities (cells/deg2) in the dorsal lateral geniculate nucleus (dLGN) of parvocellular (P) and magnocellular (M) cells, respectively, representing color-opponent and broad-band ganglion cells, with cortical magnification (mm2/deg2) gives the number of afferents per square millimeter in striate cortex (V1). For P cells, this afferent density rises only slightly with eccentricity, indicating that V1 magnification is approximately proportional to the density of P cells. The density of cytochrome oxidase puffs in V1 also rises only slightly with eccentricity. As a result, the number of P-cell afferents per puff-centered module is remarkably constant throughout V1. Our findings thus support a novel hypothesis of peripheral scaling, in which V1 cortical magnification is based on the mapping of just 1 class of afferent onto V1 modules. This "P-cell module" in V1 may be composed of submodules corresponding anatomically to the honeycomb cell in layer 4A of V1 and physiologically to a minimal complete set of color-opponent ganglion cells. In contrast, the afferent density of M cells rises steeply with eccentricity, so that the reciprocal of their afferent density, the cortical "domain" of M cells, declines with eccentricity. This decline is similar to that of point-image area in V1. As a result, the number of M cells per point-image area is nearly constant. This quantity is analogous to the receptive-field coverage factor in the retina, which for M cells is fairly constant and greater than unity at all eccentricities. The results show fundamental differences between the neural maps of these 2 major cell types, differences that are likely to have psychophysical consequences.

Visual properties of neurons in area V4 of the macaque: sensitivity to stimulus form.

Area V4, a visuotopically organized area in prestriate cortex of the macaque, is the major source of visual input to the inferior temporal cortex, known to be crucial for object recognition. To examine the selectivity of cells in V4 for stimulus form, we quantitatively measured the responses of 322 cells to bars varying in length, width, orientation, and polarity of contrast, and sinusoidal gratings varying in spatial frequency, phase, orientation, and overall size. All of the cells recorded in V4 were located on the lower portion of the prelunate gyrus. Receptive fields were located almost exclusively within the representation of the central 5 degrees of the lower visual field, and receptive field size, in linear dimension, was 4-7 times greater than that in the corresponding representation of striate cortex (V1). Nearly all receptive fields consisted of overlapping dark and light zones, like "classic" complex fields in V1, but the relative strengths of the dark and light zones often differed. A few cells responded exclusively to light or dark stimuli. Many cells in V4 were selective for stimulus orientation, and a few were selective for direction of motion as well. Although the median orientation bandwidth of the orientation-selective cells (52 degrees) was wider than that reported for oriented cells in V1, approximately 8% of the oriented cells had bandwidths of less than 30 degrees, which is nearly as narrow as the most narrowly tuned cells in V1. The proportion of cells selective for direction of motion (13%) was not markedly different from that reported in V1. The large majority of V4 cells were tuned to the length and width of bars, and the "shape" of the optimal bar varied from cell to cell, as has been reported for cells in the dorsolateral visual area (DL) of the owl monkey, a possible homologue of V4 in the macaque. Preferred lengths and widths varied independently from approximately 0.05 to 6 degrees, with the smallest preferred bars about the size of the smallest receptive fields in V1 and the largest preferred bars larger than any fields in V1. The relationship between the size of the optimal bar and the size of the receptive field varied from cell to cell. Some cells, for example, responded best to bars much narrower or shorter than the field, whereas other cells responded best to bars that filled (but did not extend beyond) the excitatory field in the length, width, or both dimensions.(ABSTRACT TRUNCATED AT 400 WORDS)

Visual responses from cells in striate cortex of monkeys rendered chronically 'blind' by lesions of nonvisual cortex.

Chronic 'blindness' can be produced in monkeys by a large cortical removal that spares modality specific visual cortex (striate, prestriate, and inferior temporal cortex). To understand the reasons for the blindness we compared single unit activity recorded from striate cortex of these monkeys with the activity of units recorded from seeing animals. The results indicate that visual processing in the striate cortex of the blind monkeys, with the exception of changes attributable to a partial disruption of the geniculostriate pathway, is similar to that of the normal monkeys. The chronic blindness is therefore probably due not to dysfunction within striate cortex but rather to a disconnection from critical processing stages within the ablated territory. Feedback from this territory is apparently not necessary for information processing to occur in striate cortex.

Density profile of blue-sensitive cones along the horizontal meridian of macaque retina.

Intravitreal injection of some fluorescent and nonfluorescent tissue-reactive dyes results in selective intracellular staining of a specific population of cones of macaque retina that have been identified tentatively as blue-sensitive cones. This paper describes quantitative density profiles of these cones as a function of retinal eccentricity. These profiles were measured from 0 deg to about 60 deg eccentricity along the nasal and temporal segments of the horizontal meridian of macaque retina. Stained cones were found to be absent from the very center of the fovea. These cones reach peak densities at 0.75-1.50 deg eccentricity, and decrease with greater eccentricity, more rapidly on the temporal than on the nasal segment of the horizontal meridian. Peak densities were found to be slightly closer to the foveal center of the retinas of adult male than of adult female macaques. Packing patterns of stained and unstained cones are discussed as is the mathematic expression of stained cone distribution. The spatial properties of the retinal distribution of stained cones agree very closely with those obtained in psychophysical human studies and other anatomic simian studies of blue-sensitive cones.

Contour, color and shape analysis beyond the striate cortex.

The corticocortical pathway from striate cortex into the temporal lobe plays a crucial role in the visual recognition of objects. Anatomical studies indicate that this pathway is mainly organized as a serial hierarchy of multiple visual areas, including V1, V2, V3, V4, and inferior temporal cortex (IT). As expected from the anatomy, we have found that neurons in V4 and IT, like those in V1 and V2, are sensitive to many kinds of information relevant to object recognition. In the spatial domain, many V4 cells exhibit length, width, orientation, direction of motion and spatial frequency selectivity. In the spectral domain, many V4 cells are also tuned to wavelength. Thus, V4 is not specialized to analyze one particular attribute of a visual stimulus; rather, V4 appears to process both spatial and spectral information in parallel. A special contribution of V4 neurons to visual processing may lie in specific spatial and spectral interactions between their small excitatory receptive fields and large silent suppressive surrounds. Thus, although the excitatory receptive fields of V4 neurons are small, the responses of V4 neurons are influenced by stimuli throughout a much larger portion of the visual field. In IT, neurons also appear to process both spatial and spectral information throughout a large portion of the visual field. However, unlike V4 neurons, the excitatory receptive fields of IT neurons are very large. Many IT neurons, for example, are selective for the overall shape, color, or texture of a stimulus, anywhere within the central visual field. Together, these results suggest that within the areas of the occipito-temporal pathway, many different stimulus qualities are processed in parallel, but the type of analysis may become more global at each stage of processing.

Non-fluorescent dye staining of primate blue cones.

The intravitreal injection in macaque retina of the fluorescent dye Procion yellow can selectively label a specific cone population whose eccentricity distribution and angular separation are consistent with those of the blue-sensitive cones of human and non-human primate retinas. Because at the concentrations used the dye is poorly visible in conventional light microscopy, fluorescence microscopy is required for the observation of the stained cones. In this paper we describe several alternative methods for the staining of blue cones in primate retina, staining that can be visualized in conventional light microscopy and, with some methods, electron microscopy.

Is there a high concentration of color-selective cells in area V4 of monkey visual cortex?

1. Recordings were made from neurons located within the central-field representation of the V4 area of extrastriate visual cortex using a semichronic, nitrous-oxide preparation; the properties of 174 cells were examined in sufficient detail to permit their classification. Cyto- and myeloarchitectural studies confirmed the identification of the area. 2. Color-selective cells with either color-biased or color-opponent properties represented about 20% of the examined population. Their incidence was not significantly different from that of similar cells encountered in penetrations into the central-field representation of area V2. 3. Most color-selective cells had color-biased properties, responding best to wave-lengths shorter than 460 nm, or longer than 580 n, or both. No examples of "green-biased" cells were found. Some color-biased cells responded to photopically matched white light, while others did not. Very few cells showed overt color-opponent responses. The spectral sensitivity of color-selective cells was not unusually narrow. 4. Cells lacking color selectivity and responding equally well to chromatic and achromatic lights of equal photopic luminosity, were the most commonly encountered cell type in penetrations of different parts of the V4 area (56%). Other than color, these cells showed stimulus preferences like those of color-selective cells. 5. One-fourth of V4 cells could not be systematically driven with the various stimuli used. This finding is consistent with recent results of recordings from the prelunate gyrus of the behaving monkey suggesting that some V4 cells receive extraretinal signals. 6. Our results do not support recent claims that V4 is specialized in the detailed analysis of color information.

Spectral bandwidths of color-opponent cells of geniculocortical pathway of macaque monkeys.

1. The spectral-response bandwidth and peak sensitivity of the responses of color-opponent retinal ganglion cells of the macaque monkey were examined in conditions of neutral adaptation. Color-opponent cells showed specific "signatures" in plots of response bandwidth versus wavelength of the peak sensitivity that allow for an acceptable estimate of the cone types whose signals mediate cell responses. 2. Averaged spectral bandwidths of color-opponent ganglion cells were compared with published data from color-selective neurons of subsequent levels of the geniculocortical pathway, including the extrastriate area termed V4. No significant differences were found between color-selective cells of the retina, dorsal lateral geniculate body, striate cortex, and V4. 3. The spectral location of the peak sensitivity of responses of the various types of color-opponent ganglion cells showed a relatively broad distribution, loosely clustering at some spectral loci. Comparison of such distribution with that of recently reported V4 cells response indicates that a remarkable scarcity of "blue/yellow" opponent responses in such reports. 4. In association with more recent electrophysiological studies of V4 cells, the results do not support current claims of a color specialization of this extrastriate area, and suggest lack of significant spectral tuning of the retinal output in, so far known, higher visual centers having color-selective cells.

Staining of blue-sensitive cones of the macaque retina by a fluorescent dye.

Intravitreal injection of a fluorescent dye, Procion yellow, results in the complete and systematic staining of a cone population in the monkey retina. These cones form an approximately regular array whose separation varies with retinal eccentricity. They are absent in the very center of the fovea, and their density peaks at 1 degree. The distribution of stained cones resembles that reported for blue-sensitive cones of other primates and, consistent with such an identification, they are found with less incidence in species having lower concentrations of blue cones.

Protan-like spectral sensitivity of foveal Y ganglion cells of the retina of macaque monkeys.

1. The spectral sensitivity of two varieties of macaque Y ganglion cells with a centre-surround organization, type III (non-colour opponent) and type IV (broad-band colour opponent), was examined with test stimuli of different size, shape and wave-length. 2. The spectral sensitivity of type III cells to large stimuli decreased at the long wave-lengths with decreasing retinal eccentricity; this change was due to a lower sensitivity of green-sensitive than of red-sensitive cone input to the surround of foveal cells, which resulted in stronger surround antagonism at the long than at the short wave-lengths leading to a rudimentary form of colour opponency. 3. The spectral properties of foveal type III cells were intermediate between those of perifoveal type III cells, whose surrounds receive a rather similar input from both cone types, and of the predominantly foveal type IV cells, whose surrounds appeared to lack input from green-sensitive cones. 4. The results indicate that both cell types represent varieties within a continuum of a single macaque Y-cell system which has a reduced long-wave-length sensitivity in the foveal region. The fact that a similar reduction of long-wave-length sensitivity can be observed in (foveal) macaque photopic luminosity functions measured with different techniques by different authors suggest that both types of Y cell have an important role in the processing of luminance information.

Composition of geniculostriate input ot superior colliculus of the rhesus monkey.

1. In order to examine the composition of the geniculostriate input to the superior colliculus, microelectrode recordings were undertaken in this structure of the rhesus monkey while parvocellular or magnocellular laminae of the LGN were reversibly inactivated by injecting minute quantities of lidocaine or MgCl2. 2. The inactivation of magnocellular laminae disrupted the visually driven activity of most cells in the topographically corresponding areas of the colliculus, but not in the superficial retinotectal recipient zone. The inactivation of parvocellular lamina had no effect on the visually driven activity of collicular cells. 3. Several controls were carried out to rule out the possibility of intervention with fibers of passage. We ascertained that the LGN injections did not affect the direct retinotectal pathway by comparing the effect of such inactivation with the effect produced by reversibly cooling visual cortex. These two manipulations yielded similar results: cells in the most superficial regions of the superior colliculus were unaffected by both cortical cooling and by magnocellular injections, while below this region the response of collicular cells was reduced or eliminated in both cases. 4. These results suggest that the indirect visual pathway to the superior colliculus via cortex is activated selectively by the broad-band system, which is relayed through magnocellular LGN. The color-opponent system does not appear to have a corticotectal input sufficient to drive collicular cells independently.