Different Temporal Patterns of Specific and General Autobiographical Memories across the Lifespan in Alzheimer's Disease.

Nathalie Philippi,Liliann Manning,François Rousseau,Stéphane Kremer,Vincent Noblet,Frédéric Blanc,Benjamin Cretin,Anne Botzung,Olivier Després

doi:10.1155/2015/963460

Abstract

We compared specific (i.e., associated with a unique time and space) and general (i.e., extended or repeated events) autobiographical memories (AbM) in Alzheimer's disease (AD). The comparison aims at investigating the relationship between these two components of AbM across the lifespan and the volume of cerebral regions of interest within the temporal lobe. We hypothesized that the ability to elicit specific memories would correlate with hippocampal volume, whereas evoking general memories would be related to lateral temporal lobe. AbM was assessed using the modified Crovitz test in 18 patients with early AD and 18 matched controls. The proportions of total memories—supposed to reflect the ability to produce general memories—and specific memories retrieved were compared between AD patients and controls. Correlations to MRI volumes of temporal cortex were tested. We found different temporal patterns for specific and general memories in AD patients, with (i) relatively spared general memories, according to a temporal gradient that preserved remote memories, predominantly associated with right lateral temporal cortex volume. (ii) Conversely, the retrieval of specific AbMs was impaired for all life periods and correlated with bilateral hippocampal volumes. Our results highlight a shift from an initially episodic to a semantic nature of AbMs during AD, where the abstracted form of memories remains.

Highlights

Autobiographical memory, which includes both episodic memories and memories belonging to personal semantics, allows a person to remember their personal past recollections and is important for the construction process of personal identity [1]
To the existence of general autobiographical memory (AbM) in young and healthy subjects (e.g., [7]), studies of AbM during normal ageing (e.g., [8,9,10]), emotional disorders [11], and neurological disorders such as Alzheimer’s disease (AD; e.g., [12, 13]) have suggested that memories that were initially strictly episodic or “specific” may lose their contextual details and become “semanticized” or “general.” While general memories have only recently been individualized and considered as cognitively distinct from specific memories, some authors tend to assimilate them to personal semantic memory (PS) [14, 15], whereas others clearly contrast them from such personal knowledge that is not confined to a particular time or place [16] or even analyze them using the same phenomenological approach than for specific AbMs [17]
Since AD pathological processes are typically localized in the medial temporal lobe (MTL) and to a lesser extend in the lateral temporal neocortex during the early stages of the disease [38], these results suggest that the retrieval of specific memories relies on the MTL no matter how old the AbMs are

Summary

Introduction

Autobiographical memory, which includes both episodic memories and memories belonging to personal semantics, allows a person to remember their personal past recollections and is important for the construction process of personal identity [1]. Autobiographical memory (AbM) refers to personal events that a person is able to reexperience in a unique and detailed spatial and temporal context This mental time travel requires autonoetic awareness, which consists of the conscious state that accompanies the experience of remembering [2, 3]. Aside from their lack of contextual specificity, these memories differ from specific AbMs by their recollective qualities, being associated with more conceptual and less contextual details This type of memories constitutes an abstracted version of memories and stand as an intermediate level between personal knowledge and specific AbMs into the hierarchical AbM model described by Conway (the Self Memory System; [6]). Semantic knowledge stands as an integral component of specific AbMs, as well as contextual details [1, 10, 22]

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