Anterograde and retrograde amnesia in rats with large hippocampal lesions

A test of socially acquired food preferences was used to study the effects of large lesions to the hippocampal formation (HPC) on anterograde and retr ograde memory in rats. In the anterograde test, rats with HPC lesions norma lly acquired the food preference but showed a faster rate of forgetting tha n control groups. When the food preference was acquired preoperatively, HPC groups exhibited a temporally graded retrograde amnesia in which memory wa s impaired when the preference was acquired within 2 days of surgery but no t at longer delays. The results support the traditional theory that the HPC contributes to the consolidation of newly acquired information into a dura ble memory trace that is represented in other brain areas. Consistent with this view, the results indicate that, once a memory trace is consolidated, the HPC does not participate in its storage or retrieval. The possibility i s considered that extrahippocampal areas in the medial temporal lobe are ne eded to maintain a memory trace throughout its existence. (C) 2001 Wiley-Li ss, Inc.