An experimental test of the theory that visual information is stored in the inferotemporal cortex

Perception, learning and identification studied with reversible suppression of cortical visual areas in monkeys

We use cold to reversibly suppress cortical areas involved in visual perception, learning and retrieval and we found a localization of functions essential for performance of delayed match-to-sample (DMS) in anterior ventral temporal cortex, we call ventral TE (TEv). We also found a visual input for this area that is separate from the one going to the heart of inferotemporal cortex and suppressing this input also impairs performance of DMS. Suppressing the dorsal half of TE (TEd) disrupts retrieval of some, but not all complex images, and different images are disrupted in different animals. This variability within and between animals is extreme, with perfect performance on some complex images and below chance on others. We suggested that TEd represents some, but not all elements of the images. In attempting to discover what those elements might be, we found that TEd suppression disrupts the perception of small figures, but not the larger figures that they compose. We also found that it impaired the discrimination and matching of colors, without impairing the ability to detect and differentiate hues. We proposed that TEd represents the details and colors of things, but not global figures. Also, complex objects do not have a representation in one area, rather its representation involves the entire visual system, including TE with different elements of the image represented in different parts.

Learning and recall of form discriminations during reversible cooling deactivation of ventral-posterior suprasylvian cortex in the cat

Extrastriate visual cortex of the ventral-posterior suprasylvian gyrus (vPS cortex) of freely behaving cats was reversibly deactivated with cooling to determine its role in performance on a battery of simple or masked two-dimensional pattern discriminations, and three-dimensional object discriminations. Deactivation of vPS cortex by cooling profoundly impaired the ability of the cats to recall the difference between all previously learned pattern and object discriminations. However, the cats' ability to learn or relearn pattern and object discriminations while vPS was deactivated depended upon the nature of the pattern or object and the cats' prior level of exposure to them. During cooling of vPS cortex, the cats could neither learn the novel object discriminations nor relearn a highly familiar masked or partially occluded pattern discrimination, although they could relearn both the highly familiar object and simple pattern discriminations. These cooling-induced deficits resemble those induced by cooling of the topologically equivalent inferotemporal cortex of monkeys and provides evidence that the equivalent regions contribute to visual processing in similar ways.

Qualitative and quantitative features of axons projecting from caudal to rostral inferior temporal cortex of squirrel monkeys

On the basis of cortical and subcortical connections and architectonics, inferior temporal (IT) cortex of squirrel monkeys consists of a caudal region, ITC, with dorsal (ITCd) and ventral (ITCv) subdivisions; a rostral region, ITR; and possibly a third region intermediate to ITC and ITR, ITI (Weller & Steele, 1992; Steele & Weller, 1993). The present study qualitatively and quantitatively examined the terminal arborizations of 26 axons in ITR and ITI labeled by injections of biocytin or, in one case, horseradish peroxidase, in ITCv. The majority of axons gave rise to a single terminal arbor, with a small number branching into two overlapping or nearby arbors. Presumptive terminal specializations consisted of rounded, bead-like swellings, most often located en passant. All axons terminated in layer 4 of cortex, and most had additional terminations in layers 3 and 5. The total extent of each axon's terminal arbor was 125-750 microns dorsoventrally (mean = 360.6 microns) and 150-725 microns anteroposteriorly (mean = 328.1 microns; all values uncorrected for shrinkage). In most axons, especially those with larger terminal fields, boutons were not uniformly distributed, but formed 2-4 clumps (mean = 2.2), with a mean width of 149 microns, separated by narrower regions of fewer boutons. Based on a cluster analysis of characteristics of the 26 axons, axons projecting from caudal (ITCv) to rostral (ITR or ITI) IT cortex of squirrel monkeys comprised three groups that we called Type I, Type II, and Type III. Type I axons, the smallest in area extent of terminal arbor, terminated predominantly in dorsal ITR. Type III axons, largest in areal extent, and Type II axons, intermediate in areal extent, terminated in ventral ITR and throughout ITI. The three classes of axons may correspond to different types of visual information entering rostral IT cortex. The clumping of boutons suggests that individual axons terminate in limited patches within their terminal fields.

Retrieval of color and form during suppression of temporal cortex with cold

Five cryodes were implanted on each side over the dorsal aspect of inferotemporal cortex (TEd) of three monkeys. They were trained on a form discrimination and three color discriminations. Suppression of TEd with cold disrupted retrieval of the color, but not the form discriminations. The animals could find the colors in a background of shifting values of gray, indicating that the suppression did not reduce their color perception to gray. They initially had great difficulty matching red to red and green to green, although that recovered with experience. The animals tended to respond to one or the other of the colors, indicating that they could perceive and discriminate them, but, either lost information about the correct stimulus, or something from past experience was interfering with performance. We suggested that cooling TEd suppresses new and recent learning of color discriminations, but it does not suppress some previous experience that intrudes upon performance of new tasks. TEd might contain episodic information about colors necessary for performance of the immediate task.

The effects of number of stimuli and prior exposure on performance of concurrent visual discriminations during suppression of inferotemporal cortex with cold

The visual part of the temporal cortex, cytoarchitectural area TE has been split into dorsal (TEd) and ventral (TEv) subdivisions. TE has long been associated with the identification of objects. However, in order to explain retrieval deficits with suppression of prestriate cortex, but not with suppression of TE, we hypothesized that object identification might take place in a working memory in the prestriate cortex upstream from TE. Exposure to the stimuli before suppressing TEd was hypothesized to cause its contribution to be relayed to prestriate cortex in anticipation of further work with them. This predicts that during TEd suppression there is a loss of access to some long-term visual memory, and without that access, large numbers of stimuli should overwhelm the limited capacity working memory. It also predicts that prior exposure to stimuli should protect them from loss during TEd suppression. We challenged these predictions in two experiments. In the first, we tested the animals on three concurrent discriminations requiring them to retrieve 8 pairs of stimuli for each one. The animals performed well on some of the discriminations during TEd suppression, but failed on others, which is consistent with the prediction. Also, different animals failed with different stimuli. However, when we tested with only the failed discriminations, they still did badly with one or two pairs, which is not consistent with the prediction. In the second experiment, we tested them with 1, 4, 7 or 10 pairs of visual discriminations drawn from a set of 23 the animals had learned. Half of the discriminations were presented immediately before suppression and half were not.(ABSTRACT TRUNCATED AT 250 WORDS)

Retrieval of a face discrimination during suppression of monkey temporal cortex with cold

Cells in the monkey temporal cortex that respond selectively to faces suggest that monkeys might have a brain structure similar to that in humans where lesions produce prosopagnosia, but effects of lesions on retrieval of face discriminations have been ambiguous in monkeys. It is possible that the stimuli in the monkey experiments were contaminated with non-face elements that could be discriminated by other parts of the visual system. In this experiment we modified the image of a monkey face creating two faces that were identical except for their internal features. We trained monkeys to discriminate these faces and then reversibly suppressed the inferotemporal cortex with cold and tested their ability to recall them. Cooling the temporal cortex produced a severe impairment in retrieval of the discrimination that remained constant across six 40-trial replications.

Retrieval of active and inactive visual discriminations while temporal cortex is suppressed with cold

While local cooling of inferotemporal cortex (IT) impairs new visual learning, it has little effect on recall. However, in visual discriminations, there is typically extensive exposure to the stimuli before cortical inactivation. Perhaps if recall was prevented before suppression, it would fail during suppression. Three animals with cryodes covering a major part of IT were trained on two face discriminations. They were then run on one of these discriminations for 3 days to create the expectation that the task would be continued with the same stimuli, and on the 4th day, they were started with these stimuli, but after cold suppression, they were switched to a discrimination that they should not have anticipated. IT suppression prevented recall of the discrimination that had not been pre-exposed; performance dropped to chance and stayed there for 50 trials. When they were switched back to the initial pair, performance returned nearly to normal. The experiment was repeated with the role of anticipated and unanticipated stimuli reversed. It was suggested that pre-exposure to the discrimination created the expectation that the same stimuli would continue to be used, and induced information about them to be copied from IT into prestriate cortex.

Selective lesions in the temporal-hippocampal region of the rat: effects on acquisition and retention of a visual discrimination task

The first purpose of this study was to investigate whether lesions in the temporal region may affect acquisition or retention of a discrimination task. In Experiment 1, rats with lesions of the temporal cortex (TC), the lateral entorhinal cortex (LEC), or their interconnections were tested postoperatively in simultaneous brightness discrimination. The results show that neither TC lesions nor LEC lesions affected acquisition of the task, and only LEC lesions impaired retention. TC/LEC transections impaired both acquisition and retention. The second purpose was to investigate effects of hippocampal lesions and perforant path transections on the discrimination task (Experiment 2). Both hippocampal and perforant path lesions impaired acquisition of the task, whereas retention was unaffected. It is suggested that TC and LEC are primarily involved in information storing and that hippocampal function is primarily involved in information processing.