Hippocampal dysfunction during aging I: deficits in memory consolidation.

Numerous ablation studies indicate a critical role for the hippocampal system in establishing or consolidating certain types of memory. Normal aging manifests by selective neurobiological changes in the hippocampal formation and on performance of tasks that require a functional hippocampus, including retention of contextual fear conditioning. To determine if impairments in the consolidation process contribute to memory dysfunction in aging, middle-aged and aged rats were fear conditioned and subsequently received dorsal hippocampal lesions or sham surgery after a 1, 7, 14, or 28-day interval. During retention tests, middle-aged rats exhibited a temporally graded retrograde amnesia of contextual fear conditioning, whereas aged rats manifested contextual memory impairments at all intervals. We postulate that the lack of consolidation in aged animals relates to previous findings of age-related changes in neuroanatomy and neurophysiological plasticity. The present findings suggest that impaired hippocampal consolidation contributes to age-related learning and memory deficits.