Memory for Public Events in Mild Cognitive Impairment and Alzheimer’s Disease: The Importance of Rehearsal

Abstract

Ribot's law refers to the better preservation of remote memories compared with recent ones that presumably characterizes retrograde amnesia. Even if Ribot-type temporal gradient has been extensively studied in retrograde amnesia, particularly in Alzheimer's disease (AD), this pattern has not been consistently found. One explanation for these results may be that rehearsal frequency rather than remoteness accounts for the better preservation of these memories. Thus, the aim of present study was to address this question by studying retrograde semantic memory in subjects with amnestic Mild Cognitive Impairment (aMCI) (n = 20), mild AD (n = 20) and in healthy older controls (HC; n = 19). In order to evaluate the impact of repetition as well as the impact of remoteness, we used a test assessing memory for enduring and transient public events that occurred in the recent and remote past. Results show no clear temporal gradient across time periods (1960-1975; 1976-1990; 1991-2005; 2006-2011), but a better performance was observed in all three groups for enduring compared with transient events. Moreover, although deficits were globally found in both patients groups compared with HC, more specific analyses revealed that aMCI patients were only impaired on transient events while AD patients were impaired on both transient and enduring events. Exploratory analyses also revealed a tendency suggesting preservation of remote transient events in aMCI. These findings are discussed with regards to memory consolidation models.

The impact of time and repeated exposure on famous person knowledge in amnestic mild cognitive impairment and Alzheimer’s disease.

“…Those subtle visuoperceptual impairments may thus PATTERNS OF SEMANTIC DEFICITS IN aMCI AND AD 23 exacerbate their semantic deficits when stimuli are presented in the visual modality. Finally, we wanted to compare the results of the Famous Names test with another test, which assesses memory for public events (Langlois et al, 2016). For uniformity purposes, we chose to present famous stimuli of both tests in the verbal modality.…”

“…Indeed, taking into account such factors should lead to a better understanding of the nature of the retrograde memory impairment in aMCI and AD. In a recent study, Langlois et al (2016) controlled for the enduring vs. transient nature of public events, and a complex pattern of impairment emerged.…”

Retrograde Amnesia for Episodic and Semantic Memories in Amnestic Mild Cognitive Impairment

“…However, conflicting results have been reported about the presence or absence of a Ribot-like temporal gradient, with some authors reporting a significant temporal-graded amnesia in AD and aMCI [14,15,18] and others reporting no differences in memory recall between remote and recent incidents [19][20][21]. Similarly, signs of semantic RA have been reported in samples of aMCI and AD patients using tests of famous public events [22][23][24][25][26][27] and tests of famous faces or famous names [28][29][30][31][32]. But also for this type of information mixed results regarding the temporal extent and gradient of RA have been reported [22][23][24][25].…”

“…Whether earlier studies have primarily focused on how RA declines as a function of the time periods considered, i.e., from the most remote to the most recent ones, only few studies [26,27,33] have tested the impact of retrieval frequency on the extent and severity of remote episodic and semantic amnesia, as postulated by the MTT, in neurodegenerative pathology. In the first work [26], the authors assessed the recall of famous public events in early AD patients using a novel approach that allows evaluating separately how memory accuracy changes as a function of the age of the event (remote versus recent events) and retrieval frequency (more frequently versus less frequently retrieved events).…”

“…They found that in all three tasks administered (subjective memory rating task, dating accuracy task, and contextual memory task) both early AD patients and normal controls derived similar benefits from greater retrieval frequency in terms of better memory performance independently of the age of the public events they had to recall. Langlois et al [27] also investigated semantic knowledge about public events in aMCI and AD patients. They contrasted enduring events (i.e., facts that were recalled many times after their occurrence) and transient events (i.e., facts that rapidly went out of the public eye after their occurrence) through a forcedchoice test.…”