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PubMed1989

Photoreceptor topography of the retina in the adult pigtail macaque (Macaca nemestrina).

In spite of the crucial role retinal photoreceptors play in mapping optical images into a pattern of neural excitation, there are no complete studies of photoreceptor topography in any primate retina. We have measured the spatial density and inner segment areas of cones and rods across the whole mounted retinas of three adult pigtail macaques (Macaca nemestrina) and constructed maps of photoreceptor density and inner segment diameter. These retinas contain an average of 3.1 million cones (2.8-3.3 million), with an average peak foveal cone density of 210,000 cones/mm2 (190,000-260,000 cones/mm2). Cone density falls steeply with increasing eccentricity, to 100,000 cones/mm2 at 200 microns from the fovea, and to 50,000 cones/mm2 at 750 microns. Imposed on this gradient is a "streak" of higher cone density along the horizontal meridian. At equivalent eccentricities, cone density is higher in nasal and inferior retina. Cone inner segments increase in diameter from 2.3 microns at the foveal center to 11 microns in far temporal retina and 10 microns in far nasal retina. These retinas contain an average of 60.1 million rods (44.9-75.3 million). Rod density is zero within 20 microns of the foveal center, increases to the crest of a "rod ring" at the eccentricity of the optic disk, and then declines. Central rod topography is asymmetric, with higher densities in superior retina. Density along the crest of the rod ring peaks in superior retina at 177,000 rods/mm2, dips as low as 120,000 rods/mm2 along the horizontal meridian, and increases to about 150,000 rods/mm2 in inferior retina. Far peripheral rod topography is relatively symmetric around the fovea. Rod inner segment diameter ranged from 1.5 microns in the fovea to 4 microns at the temporal edge and 3.4 microns at the nasal edge of the retina. At eccentricities exceeding 6 mm, rod inner segment diameter was greater temporally than nasally. Cone inner segments cover 85-90% of the central fovea, with extrareceptor space accounting for the remainder. Cone coverage declines with increasing eccentricity to 20% at the temporal edge and 35% at the nasal edge of the retina. In contrast, rod coverage increases from zero at the foveal center to a maximum of 65% in temporal retina and 50% in nasal retina. The photoreceptor topography of the pigtail macaque is qualitatively similar to that of other macaques and to humans. Photoreceptor topography is formed by a complex interaction between regional changes in cone and rod density and inner segment diameter.

Animals↗
PubMed1990

Human photoreceptor topography.

We have measured the spatial density of cones and rods in eight whole-mounted human retinas, obtained from seven individuals between 27 and 44 years of age, and constructed maps of photoreceptor density and between-individual variability. The average human retina contains 4.6 million cones (4.08-5.29 million). Peak foveal cone density averages 199,000 cones/mm2 and is highly variable between individuals (100,000-324,000 cones/mm2). The point of highest density may be found in an area as large as 0.032 deg2. Cone density falls steeply with increasing eccentricity and is an order of magnitude lower 1 mm away from the foveal center. Superimposed on this gradient is a streak of high cone density along the horizontal meridian. At equivalent eccentricities, cone density is 40-45% higher in nasal compared to temporal retina and slightly higher in midperipheral inferior compared to superior retina. Cone density also increases slightly in far nasal retina. The average human retina contains 92 million rods (77.9-107.3 million). In the fovea, the average horizontal diameter of the rod-free zone is 0.350 mm (1.25 degrees). Foveal rod density increases most rapidly superiorly and least rapidly nasally. The highest rod densities are located along an elliptical ring at the eccentricity of the optic disk and extending into nasal retina with the point of highest density typically in superior retina (5/6 eyes). Rod densities decrease by 15-25% where the ring crosses the horizontal meridian. Rod density declines slowly from the rod ring to the far periphery and is highest in nasal and superior retina. Individual variability in photoreceptor density differs with retinal region and is similar for both cones and rods. Variability is highest near the fovea, reaches a minimum in the midperiphery, and then increases with eccentricity to the ora serrata. The total number of foveal cones is similar for eyes with widely varying peak cone density, consistent with the idea that the variability reflects differences in the lateral migration of photoreceptors during development. Two fellow eyes had cone and rod numbers within 8% and similar but not identical photoreceptor topography.

Cell Count↗
PubMed1992

Callosal and superior temporal sulcus contributions to receptive field properties in the macaque monkey's nucleus of the optic tract and dorsal terminal nucleus of the accessory optic tract.

To assess the functional contribution of the cortical input to the receptive field properties of nucleus of the optic tract (NOT) and dorsal terminal nucleus (DTN) neurons, a first set of experiments evaluated the response properties of NOT-DTN cells in monkeys with split corpus callosum. With respect to visual latency, direction specificity, directional tuning width, velocity tuning, ocular dominance, and binocular interaction, they were indistinguishable from NOT-DTN neurons in normal monkeys. However, a clear difference was found regarding the extent of the receptive fields. Whereas, in normal monkeys, NOT-DTN receptive fields include the contralateral hemifield and the fovea as well as substantial parts of the ipsilateral visual field, receptive fields in callosum-split monkeys stop abruptly at, or close to, the vertical 0-meridian and do not extend into the ipsilateral visual field. In addition, the location of the highest sensitivity within the receptive fields in callosum-split monkeys is shifted away from the vertical 0-meridian in comparison to normal animals. In a second set of experiments, we antidromically identified cortical neurons within the superior temporal sulcus that project to the NOT-DTN. These neurons were found in area MT mostly near the border of MTp or MSTl. All of them are direction selective for ipsiversive stimulus movement, and their receptive fields extend substantially into the ipsilateral visual hemifield. Neurons with other preferred directions did not project to the NOT-DTN. These results contribute to the explanation of the ipsiversive directional deficits in slow eye movements after cortical lesions, as well as the asymmetries in optokinetic nystagmus with hemifield stimulation after transection of the corpus callosum. The more general implication of the results is that a particular function of a cortical area can only be understood by knowing its subcortical connections.

Animals↗
PubMed1992

Cytoarchitecture and visual field representation in area 17 of the tammar wallaby (Macropus eugenii).

Tritiated proline was injected into one eye in the tammar wallaby and transported label was studied in the cortex after transneuronal passage through the lateral geniculate nucleus. The autoradiographic label and cytoarchitecture were used to anatomically demarcate the borders of area 17. Electrophysiological recordings from single units were done to obtain a retinotopic map of area 17. Single units in area 17 were found to have orientation sensitivity comparable to those seen in placental mammals such as cat and monkey. They could also be classified as simple, complex, and hypercomplex cells. Changes in the cortical areal magnification factor with eccentricity were found to match the drop off in retinal ganglion cell density only along the vertical meridian representation. Along the horizontal meridian, the cortical magnification falls off significantly with eccentricity, whereas the ganglion cell density shows only a mild reduction. Thus central vision, especially the binocular segment, is heavily represented at the cost of the periphery.

Animals↗
PubMed1993

Retinotopic organization of the primary visual cortex of flying foxes (Pteropus poliocephalus and Pteropus scapulatus).

The representation of the visual field in the occipital cortex was studied by multiunit recordings in seven flying foxes (Pteropus spp.), anesthetized with thiopentone/N2O and immobilized with pancuronium bromide. On the basis of its visuotopic organization and architecture, the primary visual area (V1) was distinguished from neighboring areas. Area V1 occupies the dorsal surface of the occipital pole, as well as most of the tentorial surface of the cortex, the posterior third of the mesial surface of the brain, and the upper bank of the posterior portion of the splenial sulcus. In each hemisphere, it contains a precise, visuotopically organized representation of the entire extent of the contralateral visual hemifield. The representation of the vertical meridian, together with 8-15 degrees of ipsilateral hemifield, forms the anterior border of V1 with other visually responsive areas. The representation of the horizontal meridian runs anterolateral to posteromedial, dividing V1 so that the lower visual quadrant is represented medially, and the upper quadrant laterally. The total surface area of V1 is about 140 mm2 for P. poliocephalus, and 110 mm2 for P. scapulatus. The representation of the central visual field is greatly magnified relative to that of the periphery. The cortical magnification factor decreases with increasing eccentricity, following a negative power function. Conversely, receptive field sizes increase markedly with increasing eccentricity, and therefore the point-image size is approximately constant throughout V1. The emphasis in the representation of the area centralis in V1 is much larger than that expected on the basis of ganglion cell counts in flat-mounted retinas. Thus, a larger degree of convergence occurs at the peripheral representations in the retino-geniculo-cortical pathway, in comparison with the central representations. The marked emphasis in the representation of central vision, the wide extent of the binocular field of vision, and the relatively large surface area of V1 reflect the importance of vision in megachiropterans.

Animals↗
PubMed1995

Two rules for callosal connectivity in striate cortex of the rat.

In the rat, callosal cells occupy lateral as well as medial portions of striate cortex. In the region of the border between areas 17 and 18, which contains a representation of the vertical meridian of the visual field, cells projecting through the corpus callosum are concentrated throughout the depth of the cortex. In contrast, in medial portion of striate cortex, where peripheral portions of the visual field are represented, callosal cells are preferentially found in infragranular layers. These differences in topography and laminar distribution suggest that these callosal regions, referred to as medial and lateral callosal regions in the present study, subserve different functions. We explored this possibility by analyzing the patterns of callosal linkages in these two callosal regions. We charted the location of retrogradely labeled cells within striate cortex of one hemisphere after placing restricted injections of one or more fluorescent tracers into selected sites in the contralateral striate cortex. We found the medial and lateral callosal regions have distinctly different topographic organizations. Injections into medial striate cortex of one hemisphere produced labeled cells predominantly in mirror-symmetric loci in medial portions of contralateral striate cortex. The arrangement of these connections suggests that they mediate direct interactions between cortical regions representing visual fields located symmetrically on opposite sides of the vertical meridian of the visual field. In contrast, the mapping in the lateral callosal region is reversed: injections into the 17/18a border produced labeled fields located medial to the contralateral 17/18a border, while injections slightly medial to the 17/18a border produced labeled fields located at the contralateral 17/18a border.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Extrapolating global visual field indices from local parameters in the nasal region.

The local mean and the average difference of four pairs of test locations within the 26 degrees visual field, situated above and below the horizontal nasal meridian, were used to predict the global field indices MD and CLV of the Gl glaucoma program. Out of 539 examinations (194 eyes suspected of having glaucoma), the local indices NDIFF (describing asymmetrical behavior around the nasal horizontal meridian), ND0 (the mean defect in the nasal region), and the global indices MD and CLV were calculated. Seven hundred fifty-five examinations (446 normal eyes) served as a control group. First and second examinations of 146 glaucoma suspect eyes were used to calculate the retest reliability scores for the indices in question. When analyzing the glaucoma suspects, the local index NDIFF, together with the local mean defect, ND0, yielded highly reliable estimates of the global indices MD and CLV, with a retest correlation r = 0.86 for NDIFF, and r = 0.96 for ND0. The covariance of NDIFF with CLV was r = 0.67, while the co-variance of MD with ND0 was r = 0.95. The ranges of the local indices ND0 and NDIFF were each classified into 'normal range' and 'range of suspected pathology', in analogy to the normal and pathological ranges of the global field indices. Equivalence of the local indices with the corresponding ranges of MD and CLV was investigated and the results are shown. The establishment of local indices may prove to be a powerful tool in early detection of glaucomatous damage.

Glaucoma↗
PubMed1984

Objective and subjective evaluation of cyclovergence and cyclofusion.

There is a marked dispersion in the measured results of the angle formed by the intersection of the optic disc-center-meridian with the horizontal meridian, when the cycloposition of the eyes is determined through evaluation of the position of the optic disc (with fundus photographs or indirectly with perimetry). Values of the angle ranging from 0 degree at 12 degrees are still physiological. Inside this dispersion, individual right-left asymmetries of less than 4 degrees with photography and of less than 7 degrees with monocular perimetry are still normal as well. Positional differences of less than 4 degrees in sequential testings are also in a physiological range. The motor behaviour of both eyes during cyclofusion is evaluated by means of a perimetrical analysis of the blind spot at the phase-difference haploscope. Various sensory and motor adaptation phenomena are detected by comparing objective and subjective findings in patients with cyclotropia. These phenomena are discussed in detail.

Adaptation, Ocular↗
PubMed1988

Stimulus configuration and the format of the normal sensitivity gradient.

The study investigated the effect of three distinct types of stimulus configuration on the format of the normal sensitivity gradient derived by computer assisted perimetry namely: projected stimuli; light emitting diodes (LED) with the same luminance as the perimeter bowl; and 'black hole' LED stimuli. The study comprised two separate parts: 22 age matched subjects were examined with the Dicon AP3000 and with the Topcon SBP-1000 along the 15 degrees-195 degrees meridian of the visual field of the right eye; a further 22 subjects matched for age and gender were examined along the same meridian in an identical manner with the Dicon AP2025 and with the Humphrey Field Analyser 620. The various stimulus parameters were chosen in order to provide uniformity as far as possible between the instruments. The Topcon evoked greater relative sensitivity than the Dicon at all eccentricities although the rate of change of sensitivity with increase in peripheral angle varied between the two instruments at different locations. Centrally the Dicon profile followed more closely that of Humphrey stimulus size II and beyond 5 degrees that of stimulus size I. The Topcon profile followed that of the Humphrey stimulus size II both centrally and peripherally in spite of being geometrically closer to the size III stimulus. It is proposed that the variations in the sensitivity gradient are not exclusively related to stimulus size and spatial summation; the accommodative stimulus of the 'black hole' LED stimuli, stimulus colour and thresholding strategy may all be contributing factors.

Adult↗
PubMed1991

Gel injection adjustable keratoplasty.

Gel injection adjustable keratoplasty (GIAK) is a new refractive surgical procedure designed for the correction of myopia by injection of a gel substance into the peripheral corneal stroma. This paper describes the GIAK technique and reports the results obtained in 21 fresh cadaveric eyes using the procedure. After a deep interlamellar canal has been dissected with a helicoid spatula surrounding the visual axis, the gel is injected under keratometric control. In the 1st group of 14 eyes, the degree of correction varied from 2.2 to 12.8 D; there was a direct relationship between the amount of gel injected and the keratometric change. In the 2nd group of 7 eyes, the adjustability of the procedure was demonstrated. Through partial extraction of the gel and subsequent modification of the corneal curvature, the previously induced keratometric changes could be reversed or altered to a specific extent. Following the initial injection of gel to a targeted flattest meridian power of 35 D, an average value of 35.8 +/- 0.5 D was achieved in these eyes. We subsequently attempted to increase the flattest meridian to 40 D by partial removal of the gel and achieved a mean value of 40.2 +/- 0.4 D. Average presurgical astigmatism of 1.497 +/- 0.737 D was reduced to a postsurgical reading of 0.941 +/- 0.590 D (P = 0.005, Student's paired t-test), indicating an autocorrection by autodistribution of the gel inside the canaliculus (Laplace's law). GIAK is a simple, inexpensive procedure designed for the correction of myopia that has the added advantage of reducing preexisting astigmatism without encroaching on the visual axis.

Astigmatism↗
PubMed1993

A comparison of magnification functions in area 19 and the lateral suprasylvian visual area in the cat.

A retinotopic map can be described by a magnification function that relates magnification factor to visual field eccentricity. Magnification factor for primary visual cortex (V1) in both the cat and the macaque monkey is directly proportional to retinal ganglion cell density. However, among those extrastriate areas for which a magnification function has been described, this is often not the case. Deviations from the pattern established in V1 are of considerable interest because they may provide insight into an extrastriate area's role in visual processing. The present study explored the magnification function for the lateral suprasylvian area (LS) in the cat. Because of its complex retinotopic organization, magnification was calculated indirectly using the known magnification function for area 19. Small tracer injections were made in area 17, and the extent of anterograde label in LS and in area 19 was measured. Using the ratio of cortical area labeled in LS to that in area 19, and the known magnification factor for area 19 at the corresponding retinotopic location, we were able to calculate magnification factor for LS. We found that the magnification function for LS differed substantially from that for area 19: central visual field was expanded, and peripheral field compressed in LS compared with area 19. Additionally, we found that the lower vertical meridian's representation was compressed relative to that of the horizontal meridian. We also examined receptive field size in areas 17, 19, and LS and found that, for all three areas, receptive field size was inversely proportional to magnification factor.

Animals↗
PubMed1991

Topographical and topological organization of the thalamocortical projection to the striate and prestriate cortex in the marmoset (Callithrix jacchus).

In eleven hemispheres of nine marmoset monkeys (Callithrix jacchus), we have investigated the thalamo-cortical organization of the projections from the pulvinar to the striate and prestriate cortex. In each experiment, single or multiple injections of various retrograde fluorescent tracers were injected into adjacent regions or areas. In two experiments, horseradish peroxidase (HRP) was injected into the lateral geniculate nucleus (LGN) and the lateral pulvinar, respectively. The results show that the thalamo-cortical projection from LGN to striate cortex and from pulvinar to the prestriate cortex are similarly organized, but the geniculo-striate projection is more precise than the pulvinar-prestriate projection. The pulvinar-prestriate projection is topographically organized and preserves topological neighbourhood relations. Projection zones to the various visual areas are concentrically wrapped around each other. The projection zone to area 18 constitutes a central core region. It begins ventro-laterally in PuL where the pulvinar is in contact with the LGN. This contact zone we called the hilus region of the pulvinar. The area 18-projection zone stretches as a central cone into the posterior pulvinar through PuL and into PuM. It is surrounded by the projection zone to the posterior belt of area 19 and this in turn is surrounded by the projection zone to the anterior belt of area 19. The projection zones to area 19 are then surrounded medially and dorsally by zones projection to the temporal and parietal association cortex, respectively. The projection zone to area MT is located medio-ventrally in the posterior pulvinar (PuIP and surrounding nuclei) and coincides with a densely myelinated region. Area 17 also receives input from the pulvinar but probably predominantly in the region of the central visual field. The pulvinar zone projecting to area 17 is located ventrolaterally from the central core region projecting to area 18 and is contiguous laterally with the LGN. If the positions of the vertical and the horizontal meridian in the pulvinar correspond to those in the respective cortical projection zones, a second order visual field representation such as found in area 18, with the horizontal meridian split at an eccentricity of about 7-10 degrees, can also be recognized in the pulvinar.

Acetylcholinesterase↗
PubMed1991

Rostrocaudal and lateromedial density distributions of superior colliculus neurons projecting in the predorsal bundle and to the spinal cord: a retrograde HRP study in the cat.

Efferent neurons of the cat superior colliculus (SC) which project in the predorsal bundle (PDB) and to the spinal cord (PDB neurons) form a major pathway by which the SC controls the changes of the direction of gaze in response to stimuli of visual and other modalities. Knowledge of rostrocaudal and lateromedial density distributions of different groups of PDB neurons within the SC is necessary to analyse their relationships with the topography of sensory and motor maps. Density gradients may also bear on the efficacy of connections originating from topographically different collicular regions. In the present study, large injections of HRP/WGA-HRP were made in the C1 segment of the spinal cord and in the pontobulbar tegmentum. Judged by several morphological criteria, axons of passage, including those not subjected to a direct mechanical damage, were participating in the uptake of tracers. Therefore, labeled SC neurons corresponded to the nearly total populations of contralaterally projecting tectospinal neurons (TSNs) and neurons projecting in the PDB, respectively. Subtraction of the TSN density map from that of the whole PDB population was used to infer the distribution of tectal neurons terminating in the rhombencephalic tegmentum (TRhN). This subtotal labeling method proved useful in resolving the contradictions between the earlier HRP studies on the TSN and TRhN topography. The following density distributions were obtained for different groups of PDB neurons: 1) The mean TSN density is more than two times higher in the lateral half of the SC, representing the lower visual field. In this region the density remains constant from rostral to caudal, i.e., from the representation of vertical meridian to large contralateral azimuths. In the medial half, the average density decreases from rostral to caudal. Consequently, TSNs do not show the caudalward increment predicted by the higher efficacy of caudal stimulation points in eliciting head movements. 2) The distribution of PDB neurons is symmetrical with respect to the representation of the horizontal meridian. It is close to homogeneous at all azimuths of the retinotopic map and within the zone limited by small (10-15 degrees) upward and downward elevations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

On the spatial arrangement of iso-orientation bands in the cat's visual cortical areas 17 and 18: a 14C-deoxyglucose study.

The horizontal organization of iso-orientation bands in the cat's visual cortex has been investigated with the 14C-Deoxyglucose method (Sokoloff et al. 1977). Our findings suggest that in areas 17 and 18 the network formed by the bands representing one orientation comprises three basic patterns. Most frequently seen is a set of 2-4 iso-orientation bands which, straight or curved, run parallel to each other through cortical volumes usually less than 3 mm across. Beyond that distance the individual bands either end abruptly or fuse with adjacent bands. Less frequently seen are circular or triangular arrangements, or small isolated patches. Near the 17/18 border the predominant direction of the bands appears to be orthogonal to the vertical meridian, whereas in regions of areas 17 and 18 more distant from the vertical meridian the direction of the bands is more variable. In spite of irregularities in their spatial arrangement, the distance between bands and bandwidth remain constant throughout most parts of areas 17 and 18. The principles underlying the spatial arrangement of iso-orientation bands in the cat's visual cortex have yet to be identified.

Animals↗
PubMed1980

The distribution of interhemispheric projections in area 18 of the cat: coincidence with discontinuities of the representation of the visual field in the second visual area (V2).

In normal adult cats three regions with callosal projections from the contralateral visual areas 17, 18, and 19 have been identified at the lateral border of area 18 by degeneration techniques (Sanides, 1978). The visuotopic distribution of these callosal patches has now been investigated by combining anatomical with physiological techniques. The centers of the receptive fields recorded in the callosal patches are located on or close to the vertical meridian in the contralateral hemifield reaching eccentricities of about 15 deg. Some of these fields are of extraordinary size crossing the vertical meridian and covering large areas of the ipsilateral hemifield. On the other hand, receptive fields recorded from the acallosal parts of lateral area 18 may reach eccentricities of more than 50 deg. Thus, the callosal patches of lateral area 18 are wedged in between parts of lateral area 18 which represent the periphery of the contralateral hemifield. It is concluded that the retinotopic arrangement at lateral area 18 (the second visual area) distinguishes this area fundamentally from area 17, the primary visual area.

Animals↗
PubMed1985

Interhemispheric influences on area 19 of the cat.

Anatomical studies have shown an extensive network of homotopic and heterotopic interhemispheric connections in area 19 of the cat visual cortex (Segraves and Rosenquist 1982a; 1982b). We have investigated their functional organization by recording visual responses in area 19 of cats following a midsagittal section of the optic chiasm. This operation interrupts all crossed optic fibers coming both from the nasal and the temporal retinae; as a result, each hemisphere receives optic fibers only from the lateral hemiretina of the ipsilateral eye which conveys information from the contralateral visual field. Visual information transmitted to the same hemisphere from the contralateral retina and the ipsilateral visual field must be attributed to an indirect, interhemispheric pathway. We found that a rather high proportion of neurons (31.8%) in area 19 of seven split-chiasm cats responded to visual stimuli presented to the contralateral eye. All neurons receiving this interhemispheric activation were also driven by the ipsilateral eye via an intrahemispheric pathway. The property of binocularity was significantly related to the visuotopic map in that both receptive fields of each binocular neuron adjoined or were in the immediate vicinity of the vertical meridian. Due to the small size of receptive fields in area 19, the contribution of the interhemispheric pathway to the representation of the visual field is rather limited and it is certainly less extensive than that predicted by anatomical studies. The representation of the ipsilateral visual field in area 19 of intact cats, as assessed electrophysiologically, was comparable to that found in split-chiasm cats. Recordings in areas 17-18 of split-chiasm cats showed that the visual field represented through the corpus callosum in these visual areas is certainly not less and probably more, extensive than that found in area 19. The results support the conclusion that the relation to the vertical meridian and the receptive field size can explain the organization of the interhemispheric connections in the visual areas studied so far.

Animals↗
PubMed1981

Ocular dominance in striate cortex is altered by neonatal section of the posterior corpus callosum in the cat.

In adult cats that had previously undergone surgical section of the posterior corpus callosum at 13-18 days after birth, the striate cortex was examined using extracellular single unit recordings. The receptive fields of the cells examined were located from the vertical meridian to 39 degrees peripherally, and ranged from above to below the horizontal meridian. Cells were classified according to type (simple, complex), ocular dominance, receptive field size and location. Callosum sectioned cats had 53% of striate cells activated monocularly as compared to 25% for control cats. This increase in monocularly activated units primarily occurred for receptive fields in the paracentral region of the visual field, from 4-39 degrees. The age at which the neonatal surgery had occurred was correlated with the individual cat's proportion of monocularly activated cells. Therefore, the increase in monocular activation of striate units occurred within a large portion of the normal binocular visual field. This physiological change was partially predicted by a previous behavioral study showing a substantial loss in the extent of the binocular visual field following neonatal corpus callosum section (Elberger 1979).

Animals↗
PubMed1986

Visual properties and spatial distribution of neurones in the visual association area on the prelunate gyrus of the awake monkey.

We have analysed, in the awake monkey (Macaca sylvana) the functional properties of 489 neurones in the prelunate visual area (PVA, largely corresponding to V4). PVA has a coarse retinotopic organization with the lower quadrant of the visual field represented along the prelunate gyrus. The visual periphery is located medio-dorsally, the central visual field laterally near (and within?) the inferior occipital sulcus and the upper quadrant latero-ventrally. The vertical meridian runs caudally within the lunate sulcus, the horizontal meridian crosses the prelunate gyrus and continues into the superior temporal sulcus. Receptive field diameters of neurones vary between 1 degree and 10 degrees with increase towards the visual periphery, but are strictly confined to the contralateral visual field. 28% of the neurones showed spectral sensitivity. About half of these cells had strong spectral opponency, the other half showed only weak opponency with broader spectral response curves. 11 cells (2%) showed striking centre/surround interactions with inhibition, disinhibition or occlusion of the two mechanisms, and different spectral response ranges of the centre and the surround, respectively. 43% of the prelunate cells were responsive to various spatial features without spectral sensitivity. We distinguished on- and off-center cells (2%), direction and movement sensitive cells (10%) and cells sensitive to gratings of parallel lines within a limited range of orientations (about 10%). A special group were cells which responded strongly to stimuli which contained many contrasts (textures without specific orientations and without regular spatial arrangements) (9%). Many of these cells were specifically responsive to variations of the internal structure of such stimuli. 3% of the cells were strongly activated in connection with behaviour: 11 neurones discharged strongly when the monkey looked attentively at a human face or when he responded with facial expressions to a threatening expression of a person. Photographs of faces were not effective. Some neurones (1%) were activated in connection with eye movement. These neurones were found in the lateral part of the prelunate gyrus. Neurones with spectral or non-spectral properties were clustered within small, irregularly shaped patches of 1-4 mm diameter. It is concluded that the prelunate visual cortex, which we consider as part of area 19, is not just a "colour area", but represents various features of the visual environment (including colour, luminance, movement, texture and behavioral significance), and relates them - through its subcortical and cortical outputs - to behaviour.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗