Episodic memory false recognition for familiar information in Alzheimer's disease

Patients with Alzheimer's disease (AD) suffer from various types of memory distortions. We showed that confabulations are plausible memories, mainly reflecting the recall of repeated personal events mistakenly considered by confabulating patients as specific and unique events. The aim of this study is to see whether the notion that over-learned information interferes in episodic memory recall, as it does in confabulation, can be extended to another type of memory distortion, namely false recognition (i.e., a claim to recognize something that was not encountered previously). If this is the case, it should be expected that in an episodic recognition memory task AD patients produce more false recognition for well known non-studied, non to-be-remembered material than for unknown non-studied, non to-be-remembered material. In order to verify this prediction, AD patients and normal controls (NC) were administered two experiments. In Experiment 1, we presented pictures, of which half were supposed to be well known and the other half unknown monuments. For each picture, participants were asked to say whether or not the monument was known or not to them. Immediately following this semantic encoding task, participants were administered an episodic recognition memory task in which, in the same way as in the previous phase, among the non-studied items, half were supposed to be well known and the other half unknown. In Experiment 2 the same procedure was used employing well known and unknown symbols. It was predicted that AD patients make more false recognitions for non-studied well-known items than for non-studied unknown items. The results show that this is actually the case, suggesting that confusion between "uniqueness," i.e., specific unique events, and "multiplicity," i.e., repeated events, is also involved in false recognition.