Abstract
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 visual cues (black vs. white walls). In Experiment 3, less salient visual cues (striped vs. white walls) led to a robust lesion impairment, as the retrosplenial lesioned rats showed no preference for the correct corner. When subsequently trained actively to swim to the correct corner over successive trials, retrosplenial lesions spared performance on all three discriminations. The findings not only reveal the importance of the retrosplenial cortex for processing various classes of visuospatial information but also highlight a broader role in the incidental learning of the features of a spatial array, consistent with the translation of scene information.
Highlights
The study examined the importance of the retrosplenial cortex for the incidental learning of the spatial arrangement of distinctive features within a scene
Whether the retrosplenial cortex is important for compiling scene information or using that information to navigate within the environment remains, uncertain
The current experiments examined the impact of retrosplenial cortex lesions (RSC) lesions on the ability of rats to learn the location of a spatial goal with reference to either the geometric properties of the surrounding environment or the relative positions of different walls with distinctive appearances
Summary
One way to address these problems for water-maze tasks is to train the rats so that the arrangement of available spatial cues is acquired incidentally In this way, the animal learns the location of an escape platform by being repeatedly placed on the platform without being allowed to swim to the escape platform (Horne et al, 2012; Gilroy and Pearce, 2014; Kosaki et al, 2014). Part of the rationale came from the finding of retrosplenial activation in humans when viewing permanent landmarks (Auger et al, 2012) For these experiments the location of the correct corner was determined by the particular juxtaposition of distinctive colored walls, for example a black wall to the right of a white wall (Figure 1; Gilroy and Pearce, 2014). These probe trials were followed by active training in the square pool with the escape platform in the same location as had been used for passive learning
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