Selective Dysgranular Retrosplenial Cortex Lesions in Rats Disrupt Allocentric Performance of the Radial-Arm Maze Task (original) (raw)
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Effects of selective granular retrosplenial cortex lesions on spatial working memory in rats
Behavioural Brain Research, 2010
The rat retrosplenial cortex comprises two major subregions (granular and dysgranular) that differ in morphology and connectivity. Although the effects of selective dysgranular retrosplenial cortex (area 30) lesions and the effects of selective lesions within separate sub-areas of the granular retrosplenial cortex have been described, the effects of complete granular lesions (area 29) remain unknown. The present study, therefore, contrasted excitotoxic lesions of the total granular retrosplenial cortex with complete retrosplenial cortex lesions (dysgranular plus granular) using two spatial working memory tasks variably sensitive to complete retrosplenial damage. The granular retrosplenial and complete retrosplenial lesion groups were comparably impaired throughout most of radial-arm maze acquisition, including when subsequently challenged by having the maze rotated mid-trial or being tested in the dark. The other test, reinforced spatial alternation in a T-maze, provided a slightly different result as it was the rats with selective granular cortex lesions that were most impaired when the rats were tested in two, parallel mazes (one for the sample run, the other for the test run). These findings reveal the importance of the granular retrosplenial cortex for learning across a variety of different spatial tasks. Combining these findings with the results of previous functional and anatomical studies suggests that the granular and dysgranular retrosplenial subregions function in close conjunction to support spatial learning.
Testing the importance of the caudal retrosplenial cortex for spatial memory in rats
Behavioural brain research, 2003
Although there is evidence to suggest that the retrosplenial cortex is involved in spatial learning and memory, many lesion studies have left the more caudal part of this region intact so leaving its role untested. In the first experiment, rats with neurotoxic lesions of the caudal half of the retrosplenial cortex (RspC1) were tested on a reference memory task in the water-maze. The RspC1 animals were impaired on initial acquisition although they performed normally on a subsequent probe test. The second experiment looked at working memory in the radial-arm maze and water-maze. Animals with caudal retrosplenial lesions (RspC2) were unimpaired on the acquisition stage of the radial-arm maze task but were impaired when the task involved maze rotation to control for the possible use of intramaze cues. The RspC2 animals also took longer to learn the platform position on a delayed matching-to-place task in the water-maze. These results show a subtle impairment in spatial memory performanc...
Behavioural Brain Research, 2004
The present study: (1) tested the importance of the retrosplenial cortex for learning a specific heading direction and distance and, (2) determined if lesion size could explain apparent inconsistencies in the results of different research groups. Dark agouti rats received either 'complete' cytotoxic retrosplenial cortex lesions or 'standard' lesions, the latter sparing the caudal retrosplenial cortex. Animals were first tested on two versions of a "landmark" task in a water maze. In condition 1 animals could use both heading direction and allocentric position, while in condition 2 only heading direction was effective. In condition 1, animals with complete retrosplenial lesions were impaired by the end of training, their profile of performance being consistent with a failure to use allocentric position information. When the water maze task changed (condition 2) so that allocentric cues became redundant, the animals with complete retrosplenial lesions were able to head in the appropriate direction although they showed longer swim paths. Subsequent testing in the radial-arm maze provided more evidence that retrosplenial lesions can disrupt the use of distal (allocentric) room cues. The impairments seen with retrosplenial lesions were often mild but throughout the study performance of rats with 'complete' lesions was more disrupted than those with 'standard' lesions, who often did not differ from the controls. These findings show that lesion size is a critical factor and may explain why some studies have failed to find comparable deficits after retrosplenial cortex lesions.
The rat retrosplenial cortex as a link for frontal functions: A lesion analysis
Behavioural brain research, 2017
Cohorts of rats with excitotoxic retrosplenial cortex lesions were tested on four behavioural tasks sensitive to dysfunctions in prelimbic cortex, anterior cingulate cortex, or both. In this way the study tested whether retrosplenial cortex has nonspatial functions that reflect its anatomical interactions with these frontal cortical areas. In Experiment 1, retrosplenial cortex lesions had no apparent effect on a set-shifting digging task that taxed intradimensional and extradimensional attention, as well as reversal learning. Likewise, retrosplenial cortex lesions did not impair a strategy shift task in an automated chamber, which involved switching from visual-based to response-based discriminations and, again, included a reversal (Experiment 2). Indeed, there was evidence that the retrosplenial lesions aided the initial switch to response-based selection. No lesion deficit was found on an automated cost-benefit task that pitted size of reward against effort to achieve that reward ...
Behavioral Neuroscience, 2002
Despite the connections of the retrosplenial cortex strongly suggesting a role in spatial memory, the lesion data to date have been equivocal. Whether subjects are impaired after retrosplenial lesions seems to depend on whether the lesions were aspirative or excitotoxic, with the latter failing to produce an impairment. A shortcoming of previous excitotoxic lesion studies is that they spared the most caudal part of the retrosplenial cortex. The present study thus used rats with extensive neurotoxic lesions of the retrosplenial cortex that encompassed the entire rostrocaudal extent of this region. These rats were consistently impaired on several tests that tax allocentric memory. In contrast, they were unimpaired on an egocentric discrimination task. Although the lesions did not appear to affect object recognition, clear deficits were found for an object-in-place discrimination. The present study not only demonstrates a role for the retrosplenial cortex in allocentric spatial memory, but also explains why previous excitotoxic lesions have failed to detect any deficits.
The effect of retrosplenial cortex lesions in rats on incidental and active spatial learning
Frontiers in behavioral neuroscience, 2015
The study examined the importance of the retrosplenial cortex for the incidental learning of the spatial arrangement of distinctive features within a scene. In a modified Morris water-maze, rats spontaneously learnt the location of an escape platform prior to swimming to that location. For this, rats were repeatedly placed on a submerged platform in one corner of either a rectangular (Experiment 1) or square (Experiments 2, 3) pool with walls of different appearance. The rats were then released in the center of the pool for their first test trial. In Experiment 1, the correct corner and its diagonally opposite partner (also correct) were specified by the geometric properties of the pool. Rats with retrosplenial lesions took longer to first reach a correct corner, subsequently showing an attenuated preference for the correct corners. A reduced preference for the correct corner was also found in Experiment 2, when platform location was determined by the juxtaposition of highly salient...
Radial-maze performance in the rat following lesions of posterior neocortex
Behavioural Brain Research, 1981
The present experiment was designed to investigate the role of posterior neocortex (areas 17, 18 and 18a) in the maintenance of performance on the radial maze. Following training to criterion on the 8-arm radial maze, rats received either sham operations, bilateral eye enucleations, lesions of posterior neocortex, or combined enucleations and lesions of posterior neocortex. While the enucleated animals with intact brains showed a slight, but significant performance decrement relative to the sham-operated group, the other two groups, with lesions of areas 17, 18 and 18a, each showed a massive deficit. This large deficit was observed even in the group in which both the eyes and neocortex had been removed. These results suggest that the visual projection areas of cortex not only play an important role in the maintenance of accurate radial-maze performance in sighted animals, but that the integrity of these areas is necessary for the maintenance of criterion performance in blind animals.
A novel role for the rat retrosplenial cortex in cognitive control
Learning & Memory, 2014
By virtue of its frontal and hippocampal connections, the retrosplenial cortex is uniquely placed to support cognition. Here, we tested whether the retrosplenial cortex is required for frontal tasks analogous to the Stroop Test, i.e., for the ability to select between conflicting responses and inhibit responding to task-irrelevant cues. Rats first acquired two instrumental conditional discriminations, one auditory and one visual, set in two distinct contexts. As a result, rats were rewarded for pressing either the right or left lever when a particular auditory or visual signal was present. In extinction, rats received compound stimuli that either comprised the auditory and visual elements that signaled the same lever response (congruent) or signaled different lever responses (incongruent) during training. On conflict (incongruent) trials, lever selection by sham-operated animals followed the stimulus element that had previously been trained in that same test context, whereas animals with retrosplenial cortex lesions failed to disambiguate the conflicting response cues. Subsequent experiments demonstrated that this abnormality on conflict trials was not due to a failure in distinguishing the contexts. Rather, these data reveal the selective involvement of the rat retrosplenial cortex in response conflict, and so extend the frontal system underlying cognitive control.
Behavioral Neuroscience, 2003
Fornix-transected and sham-operated rats were trained on radial maze cue tasks in which the relative positions of the cues were either fixed (F condition) or varied (V condition) across trials. Proximal and distal visual stimuli were used in 2 different experiments. With proximal stimuli, fornix-transected rats were transiently impaired in the V condition and performed as well as controls in the F condition. However, using extramaze stimuli, fornix-transected rats were severely impaired in the V condition but performed normally in the F condition. According to histological analyses, performance on these cue tasks varied along with the extent of cholinergic depletion in the hippocampus. At the behavioral level, the location and stability of stimuli's relative positions seemed to have influenced rats' performance. 1 According to Eichenbaum (1994; Shapiro & Eichenbaum, 1999), Olton's concept of working memory should be more properly referred to as "episodic memory." In fact, normal rats remember a number of locations that exceeds the capacity of working memory (Roberts, 1979), and they can remember the stimuli associated with unbaited arms for durations (Knowlton, McGowan, Olton, & Gamzu, 1985) that exceed the temporal limit of working memory.
Dysgranular retrosplenial cortex lesions in rats disrupt cross-modal object recognition
Learning & Memory, 2014
The retrosplenial cortex supports navigation, with one role thought to be the integration of different spatial cue types. This hypothesis was extended by examining the integration of nonspatial cues. Rats with lesions in either the dysgranular subregion of retrosplenial cortex (area 30) or lesions in both the granular and dysgranular subregions (areas 29 and 30) were tested on cross-modal object recognition (Experiment 1). In these tests, rats used different sensory modalities when exploring and subsequently recognizing the same test objects. The objects were first presented either in the dark, i.e., giving tactile and olfactory cues, or in the light behind a clear Perspex barrier, i.e., giving visual cues. Animals were then tested with either constant combinations of sample and test conditions (light to light, dark to dark), or changed "cross-modal" combinations (light to dark, dark to light). In Experiment 2, visual object recognition was tested without Perspex barriers, but using objects that could not be distinguished in the dark. The dysgranular retrosplenial cortex lesions selectively impaired cross-modal recognition when cue conditions switched from dark to light between initial sampling and subsequent object recognition, but no impairment was seen when the cue conditions remained constant, whether dark or light. The combined (areas 29 and 30) lesioned rats also failed the dark to light cross-modal problem but this impairment was less selective. The present findings suggest a role for the dysgranular retrosplenial cortex in mediating the integration of information across multiple cue types, a role that potentially applies to both spatial and nonspatial domains.