Abstract
Autobiographical memory is commonly impaired in Alzheimer’s disease (AD). However, little is known about the very recent past which is though highly important in daily life adaptation. In addition, the impact of sleep disturbances, also frequently reported in AD, on the consolidation, and retrieval of autobiographical memories remains to be assessed. Using an adaptation of the TEMPau task, we investigated the neural substrates of autobiographical memory for recent events and the potential relationship with sleep in 14 patients with mild AD. On day 1, autobiographical memory was explored across three periods: remote (18–30 years), the last 2 years and the last month. After testing, sleep was recorded using polysomnography. The next day, AD patients benefited a resting-state 18FDG-PET scan and a second exploration of autobiographical memory, focusing on the very recent past (today and yesterday). Total recall and episodic recall scores were obtained. In addition, for all events recalled, Remember responses justified by specific factual, spatial, and temporal details were measured using the Remember/Know paradigm. Retrieval of autobiographical memories was impaired in AD, but recall of young adulthood and very recent events was relatively better compared to the two intermediate periods. Recall of recent events (experienced the day and the day preceding the assessment) was correlated with brain glucose consumption in the precuneus and retrosplenial cortex, the calcarine region, the angular gyrus, and lateral temporal areas. AD patients also provided more Justified Remember responses for events experienced the previous-day than for those experienced the day of the assessment. Moreover, Justified Remember responses obtained for events experienced before sleep were positively correlated with the amount of slow-wave sleep. These data provide the first evidence of an association between the ability to retrieve recent autobiographical memories and sleep in mild AD patients.
Highlights
Autobiographical memory is a multifaceted concept which concerns information and experiences of one’s personal life and gives a sense of self-continuity (Piolino et al, 2009)
The results reported by Eustache et al (2004) support the idea that many autobiographical memories become “semanticized” over time and that preserved remote memories in Alzheimer’s disease (AD) patients are predominantly semantic by nature, even if some remote episodic memories can persist in these patients
We have shown that both slow-wave sleep and Rapid-Eye Movement (REM) sleep are necessary for the consolidation of rich, vivid episodic memories
Summary
Autobiographical memory is a multifaceted concept which concerns information and experiences of one’s personal life and gives a sense of self-continuity (Piolino et al, 2009). Patients exhibited a deficit of autonoetic consciousness, defined as the feeling of re-experiencing or reliving the past and mentally traveling back in subjective time Contrasting with this impairment of episodic autobiographical memories, Martinelli et al (2013b) documented a preservation of personal semantic memory assessed by asking AD patients to recall generic events memory. Using the TEMPau task exploring autobiographical memory from three time periods (the last 5 years, middle age, teenage/childhood) and resting-state FDGPET imaging, Eustache et al (2004) reported a temporal gradient of recalls in favor of remote past and that right hippocampal metabolism correlated uniquely with recent memories. In an fMRI study, Meulenbroek et al (2010) contrasted the patterns of brain activity during retrieval of episodic autobiographical memories and during the processing of semantic information They reported evidence of compensatory activations, notably within frontal areas, when AD patients retrieved episodic autobiographical memories. We aimed at investigating the impact of sleep on the recall of autobiographical memories, and expected to find significant correlations between indices of sleep quality and/or quantity (such as time spent in slow-wave sleep or REM sleep) and episodic autobiographical memories
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