Entorhinal cortex lesions impair the use of distal but not proximal landmarks during place navigation in the rat.

Rats with entorhinal cortex lesions were trained in two versions of the place navigation task in the Morris water maze. In the distal condition, they had to locate the hidden platform on the basis of remote landmarks, while in the proximal condition, they had to rely only on a configuration of proximal objects, placed directly in the pool. Entorhinal rats were impaired in using distal landmarks but were able to use proximal landmarks to navigate toward the platform. These results suggest that the use of distal and proximal landmarks during navigation involves activation of different neural structures. They also suggest, in agreement with previous data, that there are two distinct landmark-processing systems, one devoted to the processing of proximal landmarks and the other to the processing of distal landmarks.