Search

Unlike simple cells, complex cells of area 18 give a directionally selective response to motion of random textures, indicating that they may play a special role in motion detection. We therefore investigated how texture motion, and especially its velocity, is represented by area 18 complex cells. Do these cells have separable spatial and temporal tunings or are these nonseparable? To answer this question, we measured responses to moving random pixel arrays as a function of both pixel size and velocity, for a set of 63 directionally selective complex cells. Complex cells generally responded to a fairly wide range of pixel sizes and velocities. Variations in pixel size of the random pixel array only caused minor changes in the cells' preferred velocity. For nearly all cells the data much better fitted a model in which pixel size and velocity act separately, than a model in which pixel size and velocity interact so as to keep temporal-frequency sensitivity constant. Our conclusion is that the studied population of special complex cells in area 18 are true motion detectors, rather than temporal-frequency tuned neurons.

Pattern vision deprivation (BD) can induce permanent deficits in global motion perception. The impact of timing and duration of BD on the maturation of the central and peripheral visual field representations in cat primary visual areas 17 and 18 remains unknown. We compared early BD, from eye opening for 2, 4, or 6 months, with late onset BD, after 2 months of normal vision, using the expression pattern of the visually driven activity reporter gene zif268 as readout. Decreasing zif268 mRNA levels between months 2 and 4 characterized the normal maturation of the (supra)granular layers of the central and peripheral visual field representations in areas 17 and 18. In general, all BD conditions had higher than normal zif268 levels. In area 17, early BD induced a delayed decrease, beginning later in peripheral than in central area 17. In contrast, the decrease occurred between months 2 and 4 throughout area 18. Lack of pattern vision stimulation during the first 4 months of life therefore has a different impact on the development of areas 17 and 18. A high zif268 expression level at a time when normal vision is restored seems to predict the capacity of a visual area to compensate for BD. ispartof: Cerebral Cortex vol:25 issue:10 pages:3515-3526 ispartof: location:United States status: published

In the primary visual cortex and higher-order areas, it is well known that the stimulation of areas surrounding the classical receptive field of a neuron can inhibit its responses. In the primate area middle temporal (MT), this surround suppression was shown to be spatially organized into high and low suppression modules. However, such an organization has not been demonstrated yet in the primary visual cortex. Here, we used optical imaging of intrinsic signals to spatially evaluate surround suppression in the cat visual cortex. The magnitude of the response was measured in areas 17 and 18 for stimuli with different diameters, presented at different eccentricities. Delimited regions of the cortex were revealed by circumscribed stimulations of the visual field (“cortical response field”). Increasing the stimulus diameter increased the spread of cortical activation. In the cortical response field, the optimal stimulation diameter and the level of suppression were evaluated. Most pixels (≥3/4) exhibited surround suppression profiles. The optimal diameter, corresponding to a population of receptive fields, was smaller in area 17 (22°) than in area 18 (36°) in accordance with electrophysiological data. No difference in the suppression strength was observed between both areas (A17: 25%, A18: 21%). Further analysis of our data revealed the presence of surround modulation maps, organized in low and high suppression domains. We also developed a statistical method to confirm the existence of this cortical map and its neuronal origin. The organization for center/surround suppression observed here at the level of the primary visual cortex is similar to those found in higher order areas in primates (e.g., area MT) and could represent a strategy to optimize figure ground discrimination.

Several brightness illusions indicate that borders can dramatically affect the perception of adjoining surfaces. In the Craik–O’Brien–Cornsweet illusion, in particular, two equiluminant surfaces can appear different in brightness due to the contrast border between them. Although the psychophysical nature of this phenomenon has been well characterized, the neural circuitry underlying this effect is unexplored. Here, we have asked whether there are cells in visual cortex which respond to edge-induced illusory brightness percepts such as the Cornsweet. Using optical imaging and single unit recordings methods, we have studied responses of the primary (Area 17) and second (Area 18) visual cortical areas of the anesthetized cat to both real luminance change and Cornsweet brightness change. We find that there are indeed cells whose responses are modulated in phase with the modulation of the Cornsweet stimulus. These cells are present in both Area 17 and Area 18, but are more prevalent in Area 18. These responses are generally weak and are found even when receptive fields are distant from the contrast border. Consistent with perception, cells which respond to the Cornsweet border are modulated in antiphase to the Narrow Real (another border-induced illusory brightness stimulus). Remarkably, we also find evidence of edge-induced responses to illusory brightness change using intrinsic signal optical imaging. Both real luminance change and edge-induced brightness change produces a greater imaged response in Area 18 than in Area 17. Thus, in the absence of direct luminance stimulation, cells in visual cortex can respond to modulation of distant border contrasts. We suggest that the perception of surface brightness was encoded in the early visual cortical pathway by both surface luminance contrast signals in Area 17 (Rossi, A. F., Rittenhouse, C. D., & Paradiso, M. A. (1996). The representation of brightness in primary visual cortex. Science, 273, 1104–7) and border-induced contrast signals that predominate in Area 18. © 2001 Published by Elsevier Science Ltd.

Associated and commisural connections of visual areas 17 and 18 were studied in the light of the latest knowledge about the anatomo-functional organization of the cat's visual cortices. Injections of L-[5-3H] proline were placed, in different animals, in area 17 or 18 of the right hemisphere. Serial histological sections of the whole brain were processed by autoradiographic technique, after long (8-16 days) or short (30 hours) survival times. Cortical areas labelled by axonally transported radioactive material were then correlated with electrophysiological and cytoarchitectonical maps. Areas 17 and 18 were found to send associational projections to area 19, to the anterior and posterior subdivisions of the lateral suprasylvian visual area and to two regions lying on the crown of the suprasylvian gyrus (areas 21A and 20). In addition, area 18 sends projections to ipsilateral areas 17, 7 and 5. Contralaterally, projections from areas 17 and 18 reach the homonymous areas near the margin of the other. Homotopical callosal connections of area 17 affect the band of the contralateral 17 in which part of the ipsilateral visual hemi-field is represented. Heterotopical commisural projections from the areas studied affect areas 19 and LS in regions adjoining the central vertical meridian representations. These results suggest that, on an anatomical basis, the interactions between the cortical targets of the classical geniculo-striate and the estrageniculo-striate systems are more complicated than previously believed. Furthermore, the geniculo-striate system supplies some visual input to non-visual areas through area 18.