Involvement of entorhinal cortex or parietal cortex in long-term spatial discrimination memory in rats: Retrograde amnesia

Twenty-four rats assigned to 1 of 3 matched groups (control, entorhinal cortex [EC], and parietal cortex [PC]) were trained on 6 successive discrimination problems (2 in an 8-arm for pretraining and 4 in a 12-arm radial maze for training per se). The training on the 12-arm maze started 6, 4, 2, and 0.5 weeks before surgery. On the day after the rats learned the last problem, they were given surgery according to groups. Postoperative retention was measured by presenting 16 trials per session for each of the problems during 4 sessions. Results indicate that the EC lesions produced a retention deficit for problems learned immediately and up to 4 weeks before surgery, but not for the problem acquired 6 weeks before the lesions. The PC lesions produced a significant retrograde amnesia that was not temporally graded. Results demonstrate that the EC and PC make important, albeit distinct, contributions to spatial memory storage and retrieval in rats.