Consolidation of object-discrimination memory is independent of the hippocampus in rats

We examined whether retrograde amnesia would be more likely for object discriminations learned an hour before hippocampal damage than object discriminations learned days before. Specifically, rats were trained on two object-discrimination problems 72 h before surgery and another discrimination problem and the reversal of one of the previously learned problems 1 h before surgery. Importantly, novel procedures that minimized overtraining on the object discriminations were used to increase the possibility of the lesions causing amnesia. After either receiving sham or neurotoxic-induced hippocampal damage, rats were tested for retention using an extinction procedure. Control rats and rats with extensive hippocampal damage displayed a strong bias for the rewarded object on each object-discrimination problem and a significant bias for the most recent contingency learned on the reversal problem. These results suggest that, despite the use of very sensitive training and testing procedures, hippocampal damage did not cause retrograde amnesia. The findings imply that the hippocampus is not critical for the consolidation, storage, or retrieval of object-reward associations, or any other information required for accurate performance of an object discrimination.