Do Rats with Retrosplenial Cortex Lesions Lack Direction?

The retrosplenial cortex is seen as a convergence point for different classes of spatial cue, yet aside from allocentric processing, little is known about other cue types that depend on the integrity of this area. Rats with bilateral retrosplenial cortex lesions were, therefore, trained on a sequence of reinforced spatial alternation tasks designed to isolate different spatial strategies. Using a standard T-maze alternation procedure, which could be solved using multiple strategies, only a marginal lesion effect was observed. Next, by using two T-mazes set side-by-side in the light, and then the dark, it was possible to examine alternation around a fixed bearing (direction alternation). Retrosplenial cortex lesions only disrupted the latter (direction alternation) condition. Direction alternation is of particular interest as it presumably taxes head-direction information, and so provides a way of behaviourally assessing the contribution of this navigation system. Finally, rats were tested on a spatial working memory task in a radial-arm maze. A retrosplenial lesion deficit appeared when the maze was rotated mid-trial, as repeatedly found in previous studies. The pattern of findings in the present study strongly indicates that retrosplenial cortex lesions impair the use of direction cues for alternation, in addition to previously established impairments for allocentric-based navigation and path integration.