A further characterization of the spatial problem-solving deficit induced by lesions of the medial frontal cortex in the rat

Abstract

Two experiments were conducted to investigate the basis of the spatial impairment displayed by rats with lesions to the medial frontal cortex, using a three-table Y-shaped apparatus. In both experiments, animals were first given an exploratory experience of the maze, followed by a short feeding experience on one of the tables, and were then required to return to the location where they had just been fed. In Expt. 1, a spatial working memory procedure was used in which the location of the goal table was varied from day to day. When compared to normal animals frontal rats showed a marked impairment, despite the addition of (a) distinctive visual cues on the tables and their associated runways, or (b) a conspicuous visual pattern placed directly above the goal. Expt. 2 used a spatial learning procedure, in which the spatial location of the goal table remained constant over days. However, the whole apparatus was daily rotated so that animals could not learn to associate the goal table with specific cues located behind it. This procedure did not prevent frontal animals from learning the consistent location of the food by using the spatial relationships of the environment. These results, together with previous ones, suggest that frontal animals suffer from a specific (though not restricted to the domain of spatial information) working memory deficit, and their spatial reference memory is not impaired.