Deterioration of the memory for historic events in patients with mild cognitive impairment and early Alzheimer's disease.

Retrograde memory decline in Alzheimer's disease (AD) and mild cognitive impairment (MCI) has been evaluated using tests of past public knowledge, such as famous personalities and events, and tests of autobiographical memory. Reports of temporal gradients (TG) in retrograde amnesia have been inconclusive. Here, we compared the remembrance of famous historic events by patients with amnesic MCI and early AD using the newly developed Historic Events Test (HET). The HET demands knowledge about famous public events of the past 60 years divided into five time segments, and consists of three tasks, Recognition, Dating Accuracy, and Contextual Memory. In both patient groups, the performance was worse than in healthy controls. Memory performance of all time segments was uniformly affected by this kind of retrograde amnesia. There was no evidence of a TG, and memory decline was similar in all three tasks of the HET. In contrast, for the same patients tested at the same time, we had previously found a TG for autobiographical memory with better preservation of remote than recent memories (Leyhe, Müller, Milian, Eschweiler, & Saur, 2009). We propose that recall of more frequently retrieved remote autobiographical facts and incidents has become independent of the hippocampus, whereas more seldomly retrieved recent autobiographical memory and knowledge of famous events remain dependent on the hippocampus and will thereby be susceptible to the early neurodegenerative damage of the hippocampus in AD. Our assumption may reconcile the Cortical Reallocation Theory and the Multiple Trace Theory.