Biomedical subjects

G A Orban

Publications and source records attributed to G A Orban.

At least 19 recordsLinked to original sources

PubMed1992

First-order analysis of optical flow in monkey brain.

Optical flow is a rich source of information about the three-dimensional motion and structure of the visual environment. Little is known of how the brain derives this information. One possibility is that it analyzes first-order elementary components of optical flow, such as expansion, rotation, and shear. Using a combination of physiological recordings and modeling techniques, we investigated the contribution of the middle superior temporal area (MST), a third-order cortical area in the dorsal visual pathway that receives inputs from the medial temporal area (MT). The results show (i) that MST cells, but not MT cells, are selective for elementary flow components (EFCs) alone or their combination with translation, (ii) that MST cells selective for an EFC do not extract this component from a more complex motion pattern, and (iii) that position invariance as observed in MST is compatible with an input arrangement from MT cells matching the selectivity of MST neurons.

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PubMed1992

Longterm impairment of cat optokinetic nystagmus following visual cortical lesions.

Binocular and monocular gain of optokinetic nystagmus (OKN), OKN dynamics, vestibulo-ocular reflex (VOR) and VOR adaptation were measured in 5 normal cats and in 5 cats which underwent bilateral visual cortical lesions involving the 17-18 complex at least 4 months before testing. We observed longterm deficits after bilateral lesions involving area 17 and variable parts of area 18 but failed to observe deficits after 18-19 lesions. These deficits were limited to the OKN gain and the build-up time constant of OKN; the VOR and the optokinetic after-nystagmus (OKAN) time constant were within normal limits. Our results suggest that areas 17-18 operate in parallel to control the encoding of retinal slip velocity at the level of the nucleus of the optic tract (NOT) and the accessory optic system (AOS), which are known to represent the initial stage of the optokinetic pathways.

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PubMed1992

Texture segregation in the cat: a parametric study.

We have investigated how different texture parameters affect texture segregation in the cat, and which strategies cats use to solve the segregation task. Five cats were presented with stimuli consisting of two adjacent panels. One side contained a square area of a particular texture embedded in a different background texture; the other side was filled with only the background texture. The animal's task was to detect at which side the texture difference was presented. Sensitivity for the texture difference was assessed by making one aspect of the texture (in most instances the size of the texture elements) dependent upon performance by means of a staircase procedure. Among the most prominent parametric effects are those of density and element position randomization. In general, segregation was optimal at intermediate densities and deteriorated at larger and smaller densities. Element position randomization caused a slight but systematic decrease in segregation performance. Furthermore, we found texture elements at the border between different textures to be of primary importance for segregation. Which strategy the animals used for solving the segregation task depended upon the presence of random figure/background reversals in subsequent stimulus presentations during training. The animals learned to detect texture differences if these reversals were present, and without reversals, they learned to identify the particular texture in the target square. Interestingly, parameter dependencies of segregation did not depend upon the detection strategy used. We have speculated that the two different strategies used by the cats to solve the segregation tasks are related to different hierarchical levels of texture segregation which can be traced back to different stages of texture processing in human models of segregation performance.

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PubMed1991

Distribution of somatostatin receptors in the cat and monkey visual cortex demonstrated by in vitro receptor autoradiography.

Somatostatin (SRIF, S14) receptors in the cat and monkey visual cortex were visualized by means of in vitro autoradiography with an iodinated agonist of SRIF, [125I-Tyr0,DTrp8]S14. The kinetics, performed on tissue sections, revealed an apparently single, saturable site (KD = 3.92 +/- 0.31 10(-10) M for the cat, and 3.82 +/- 0.28 10(-10) M for the monkey visual cortex) with pharmacological specificity for S14 and [DTrp]-substituted S14. Autoradiography, performed on frontal sections of the cat and monkey visual cortex, revealed a heterogeneous regional and laminar distribution of SRIF receptors. In cat areas 17, 18, and 19, SRIF receptors occur mainly in the supragranular layers, although small interareal and intra-areal differences are observed. The infragranular layers (V-VI) in area 19 contain a significantly higher proportion of SRIF receptors compared to both areas 17 and 18. In the antero- (AMLS) and posteromedial lateral suprasylvian area (PMLS), layers V and VI contain the highest proportion of SRIF receptors. This latter pattern is also observed in the area prostriata medially adjoining area 17 in the splenial sulcus. In the monkey visual cortex, areas 17 and 18 exhibit similar distribution patterns, SRIF receptors being primarily concentrated in layers V and VI. Neither in the cat nor the monkey visual cortex could we observe significant differences in SRIF receptor distribution between different retinotopic subdivisions within one area.

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PubMed1991

Subtraction inhibition combined with a spiking threshold accounts for cortical direction selectivity.

We have modeled simple-cell direction selectivity by a nonlinearity consisting of a subtraction inhibition followed by half-wave rectification and compared the performance of this model to that of different versions of the elaborated Reichardt detector for similar inputs and parameter settings. Not only does the subtraction model fit the experimental data more closely than the elaborated Reichardt detector, but the subtraction model also is more plausible from a physiological and anatomical point of view. Moreover, the subtraction model operates optimally at plausible spatiotemporal parameter settings. Therefore, we conclude that there is no need to invoke specific synaptic interactions, such as implied in the Reichardt detector, to account for simple-cell direction selectivity.

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PubMed1991

Orientation discrimination in the cat: its cortical locus. I. Areas 17 and 18.

An elementary unit of visual pattern and form perception is thought to be the orientation of edges; this element has been studied extensively by neurophysiologists using oriented line segments or bars. These same stimuli have been used in the present study to measure threshold discriminations in cats before and after cortical lesions of areas 17 and/or 18. Control experiments showed that the discriminations were made by using a single cue, orientation, and that other stimulus parameters, width, length and contrast of the bar, were optimized. The extent of the lesions was evaluated anatomically from cell and fiber stained sections through cortex and thalamus, matched to retinotopic maps of Tusa et al. (Cortical Sensory Organization, Vol. 2, Humana Press, pp. 1-31, '81) and Sanderson (Journal of Comparative Neurology 143:101-118, '71), and physiologically from visual field position of receptive fields of cells recorded in areas neighboring the lesions. Lesions involving area 17 and large parts of area 18 produced a marked deficit in orientation discrimination which included a loss in retention, and after retraining a substantial increase in thresholds for up to 3 years when tested with long bars. There was no recovery of discrimination when the animals were tested with short bars. Lesions which involved area 17 plus small parts of 18, or lesions of areas 18 and 19, produced no retention deficit and resulted in an increase in thresholds only at low contrast and narrow width. These experiments revealed an excellent correlation between lesion locus and size and behavioral deficit. They indicate that the cortical representation of bar orientation used for discrimination is distributed within and across areas 17 and 18. The spread of the distribution depends on other stimulus parameters such as bar width and length. Furthermore the experiments show that neither the most narrowly tuned cells nor the X-cell system is required for fine orientation discrimination of a long bar.

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PubMed1991

Laminar and regional distribution of galanin binding sites in cat and monkey visual cortex determined by in vitro receptor autoradiography.

The distribution of galanin (GAL) binding sites in the visual cortex of cat and monkey was determined by autoradiographic visualization of [125I]-GAL binding to tissue sections. Binding conditions were optimized and, as a result, the binding was saturable and specific. In cat visual cortex, GAL binding sites were concentrated in layers I, IVc, V, and VI. Areas 17, 18, and 19 exhibited a similar distribution pattern. In monkey primary visual cortex, the highest density of GAL binding sites was observed in layers II/III, lower IVc, and upper V. Layers IVA and VI contained moderate numbers of GAL binding sites, while layer I and the remaining parts of layer IV displayed the lowest density. In monkey secondary visual cortex, GAL binding sites were mainly concentrated in layers V-VI. Layer IV exhibited a moderate density, while the supragranular layers contained the lowest proportion of GAL binding sites. In both cat and monkey, we found little difference between regions subserving central and those subserving peripheral vision. Similarities in the distribution of GAL and acetylcholine binding sites are discussed.

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PubMed1991

Calcium binding proteins as molecular markers for cat geniculate neurons.

Immunocytochemistry revealed that in the cat dorsal lateral geniculate nucleus (dLGN) almost all parvalbumin-positive cells are GABAergic and about 56% of the calbindin D-28K (calbindin-immunoreactive neurons are also GABA-positive. On the other hand, in the same nucleus, almost all GABAergic neurons contain parvalbumin, and about 89% of the GABA-immunoreactive neurons contain calbindin. Double-labeling with calbindin and parvalbumin revealed that approximately 50% of the immunoreactive neurons are double-stained. In the PGN, virtually all neurons are GABA and parvalbumin-positive. Only a few scattered cells were also calbindin-immunoreactive. These results show that GABAergic geniculate cells can be differentiated on the basis of their calcium-binding protein immunoreactivity. Four types of immunoreactive cells are described here: (1) cells positive for GABA, parvalbumin and calbindin, (2) cells positive for GABA and parvalbumin, but negative for calbindin, (3) cells negative for GABA and parvalbumin, but positive for calbindin, (4) cells negative for GABA, parvalbumin and calbindin.

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PubMed1991

Calcium binding proteins and neuropeptides as molecular markers of GABAergic interneurons in the cat visual cortex.

In the cat visual cortex, almost all parvalbumin-positive cells are GABAergic, and about 80% of the calbindin D-28K-positive neurons are also GABA-immunoreactive. About 37% of the GABAergic neurons contain parvalbumin and a smaller fraction (about 18%) contains calbindin. Furthermore, parvalbumin and calbindin are localized in two separate neuronal populations in the cat visual cortex, suggesting that two GABAergic populations can be distinguished, one containing parvalbumin and one containing calbindin. Double staining for parvalbumin and neuropeptides (CCK, SRIF and NPY), revealed no double-labeled cells, with the exception of a few SRIF- and parvalbumin-positive neurons. These results show that cortical GABAergic cells can be differentiated on basis of their calcium binding protein and neuropeptide immunoreactivity.

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PubMed1991

Quantitative study of striate single unit responses in monkeys performing an orientation discrimination task.

Contour orientation discrimination accuracy is determined by the orientation bandwidth, response variance and response strength of single units that code for orientation. We measured the latter three properties for V1 cells of monkeys which were performing an orientation discrimination of the grating stimulating the cell under study. We recorded from 285 cells, of which 76% responded to the grating. The orientation bandwidth, measured as full width at half height of the tuning curve, varied over a wide range amongst cells. The median bandwidth was 41 degrees. The response variance of the cells also varied considerably between cells; on average it was about two times the response strength. We also studied the temporal properties of the responses. Most of our cells had a latency between 40 and 100 ms. The response variance was found to be smaller in the initial phases of the response than at the later response stages. In some cells the orientation tuning varied in successive stages of the response, while in others the orientation bandwidth and preferred orientation remained stable throughout the response. However, all orientation sensitive cells were orientation tuned from the start of the response, a property which contribute to the fast and reliable coding of contour orientation. These results provide for the first time an estimation of the orientation tuning properties of V1 cells during visual orientation discrimination. They will be very useful to compare single cell properties of other areas to as well as in simulation studies of models of primate visual discriminations.

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PubMed1990

Staircase procedure and constant stimuli method in cat psychophysics.

We measured 73.5% correct just noticeable differences (JNDs) in bar orientation with the method of constant stimuli and with a Wetherill and Levitt staircase procedure, using a total of 25 cats. For the same number of trials per threshold assessment, the variability of the threshold remained independent of the testing method used. However, the JNDs measured using the method of constant stimuli were significantly influenced by the range of the orientation differences (ODs) utilized for measuring the JND. This effect was particularly large in incompletely trained cats, but it also was significant in extensively trained subjects. On the other hand, staircase threshold measurements were not affected by the starting OD, independently of how well the animals had been trained. This shows that the staircase procedure is a more efficient instrument with which to measure JNDs in orientation than is the method of constant stimuli. With the staircase procedure, we found that the JNDs measured at oblique reference orientations did not exceed those measured at principal reference orientations (no oblique effect). Two earlier studies from this laboratory using the method of constant stimuli did report an oblique effect. Our data suggest that this oblique effect might stem from a less efficient training at the right oblique reference orientation in these studies, combined with a relatively inefficient testing procedure such as the constant stimuli method.

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PubMed1990

Illusory contour orientation discrimination in the cat.

We present the first evidence that a non-human species (the cat) is able to discriminate the orientation of illusory contours. Following Vogels and Orban45, we used two types of illusory contours. In one type, the illusory contour was defined by a number of contour-inducing semicircles, of which the endpoints were separated by a gap. In the other pattern, the inducing semicircles were shifted in phase along their diameter and their endpoints were aligned along the contour. Just noticeable differences in orientation were measured (at the 73.5% correct level), using a Wetherill and Levitt49 staircase procedure. Values in the order of 11 degrees were obtained when using the first type of illusory contour. Just noticeable differences with the second type were in the order of 17 degrees. Reducing the salience of the illusory contour, whether by scrambling the contour, or by decreasing the number or the contrast of inducing semicircles, systematically increased discrimination thresholds.

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PubMed1990

Regional distribution of binding sites for neuropeptide Y in cat and monkey visual cortex determined by in vitro receptor autoradiography.

The goal of this study was to elucidate the precise regional and laminar distribution of neuropeptide Y (NPY) binding sites in feline and primate visual cortex. By means of in vitro receptor autoradiography, NPY binding sites in primate and feline visual cortex were specifically labeled with 3H-NPY. In cat area 17, the highest density of NPY-binding sites was present in lamina I and the upper half of lamina II. The density then gradually decreased towards lamina VI. Areas 18 and 19 exhibited a similar binding site-density profile. The decrease in density from superficial to deep layers was more gradual in area 18 than in areas 17 and 19. In monkey primary visual cortex (V1), layer IVc presented a high concentration of NPY binding sites, in addition to a dense zone of binding sites in layer I. Monkey secondary visual cortex (V2) displays a similar dense zone in layer I, but lacks such high density of NPY binding sites in layer IV. Therefore, the border between primary and secondary visual cortex coincides with the abrupt disappearance of this latter high density in layer IV. In cat as well as in monkey visual cortex, no significant differences were found between regions representing central vision and those representing the peripheral parts of the visual field. Comparison of our results for NPY binding sites with the distribution of alpha 1-adrenergic receptors, as recently described by Rakic et al. (J. Neurosci. 8(10):3670-3690, 1988) for primate and Parkinson et al. (Brain Res. 457:70-78, 1988) for feline visual cortex, revealed that those two patterns are very similar.

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PubMed1990

Influence of retinal lesions on grating acuity of the cat.

Grating acuity was investigated behaviorally in the cat. Retinal lesions of increasing diameter centered on the area centralis were made by photocoagulations in one eye, while the intact eye was used as control. Lesion size evaluated from fundus photographs was precisely correlated with the anatomical lesion size measured in retinal whole mounts. Grating acuity improved with increasing grating area in cats with intact retinae and after small (less than 3 degrees diameter) retinal lesions but not after large lesions (greater than 4 degrees diameter). Overall, grating acuity clearly decreased when lesions became larger than 4 degrees in diameter. The acuity-eccentricity relationship closely fits the cutoff frequency of brisk sustained cells at the corresponding eccentricities.

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PubMed1990

Speeding up visual discrimination learning in cats by differential exposure of positive and negative stimuli.

We have developed an adaptive training method which considerably reduces the total time required to train cats to threshold in an orientation discrimination task. During training, the animals are given greater exposure in time to the positive stimulus compared to the negative one. Therefore, this method has been coined the differential exposure method (DEM). The greater exposure to the positive stimulus reduces the number of errors an animal commits during training and thereby enhances speed of learning. Indeed, with the DEM, 34 daily sessions sufficed to train cats to threshold for 2 different reference orientations. Furthermore, the DEM was effective not only for simple stimuli such as real bars but also for complex stimuli such as illusory contours. Finally, the DEM was equally effective for training naive cats which had undergone large visual cortical lesions as it was for normal animals.

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PubMed1990

Corticofugal feedback influences the responses of geniculate neurons to moving stimuli.

Geniculate cell responses to moving bars and moving texture were compared in normal cats and in cats in which the corticofugal feedback was removed by cortical ablation. In experimental animals the response strength and the velocity upper cutoff assessed with a moving bar was reduced compared to control animals. The strength of response to texture decreased even more after cortical ablation, which also changed the response pattern of X cells to moving texture. These data suggest that corticofugal feedback contributes to the geniculate responses to moving stimuli and in particular to moving texture.

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PubMed1990

Responses of visual cortical neurons to curved stimuli and chevrons.

Single cells were recorded in area 17 of anaesthetized and paralyzed cats and their responses to curved stimuli and chevrons compared. Striate cells exhibited three different response patterns. A first group responded optimally to a straight line (i.e. zero curvature) and responded similarly to chevrons and to curved lines. A second group responded to all curvatures and was broadly tuned for the straight line when tested with chevrons. A third group responded only to large curvatures, many (2/3) to both signs of curvature and a number (1/3) to only one sign. Cells in this group responded differently to chevrons and curved lines. Cells in these three classes differed both in length-response curve and in width of orientation tuning. Laminar analysis revealed that the three classes are distributed differently across cortical layers. These data shed new light on the finding of Malpeli and coworkers that orientation is extracted at least twice in a cortical column.

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PubMed1990

Bar orientation discrimination in the cat.

We have measured orientation-discrimination thresholds of 4 deg in the cat, confirming an earlier study of Vandenbussche and Orban (1983). Unlike Vandenbussche and Orban (1983), we found that orientation-discrimination performance is not better at principal, as compared to oblique, reference orientations (no oblique effect). Despite the absence of the oblique effect, and despite the discrimination thresholds which were elevated by a factor of 4 compared to humans, orientation-discrimination performance of cats and humans is qualitatively similar in a number of aspects. First, orientation-discrimination performance as a function of length and contrast is qualitatively similar to human performance. Second, as in humans, detection and discrimination of the stimuli are closely related. Finally, randomizing the contrast between the stimuli does not affect orientation-discrimination performance. This suggests that similar computations underlay orientation-discrimination performance in both species. In summary, our results confirm that the cat is a useful model for human orientation-discrimination performance.

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