Everyday episodic memory in amnestic mild cognitive impairment: a preliminary investigation.

Muireann Irish,Brian A Lawlor,Robert F Coen,Shane M O'Mara

doi:10.1186/1471-2202-12-80

Abstract

BackgroundDecline in episodic memory is one of the hallmark features of Alzheimer's disease (AD) and is also a defining feature of amnestic Mild Cognitive Impairment (MCI), which is posited as a potential prodrome of AD. While deficits in episodic memory are well documented in MCI, the nature of this impairment remains relatively under-researched, particularly for those domains with direct relevance and meaning for the patient's daily life. In order to fully explore the impact of disruption to the episodic memory system on everyday memory in MCI, we examined participants' episodic memory capacity using a battery of experimental tasks with real-world relevance. We investigated episodic acquisition and delayed recall (story-memory), associative memory (face-name pairings), spatial memory (route learning and recall), and memory for everyday mundane events in 16 amnestic MCI and 18 control participants. Furthermore, we followed MCI participants longitudinally to gain preliminary evidence regarding the possible predictive efficacy of these real-world episodic memory tasks for subsequent conversion to AD.ResultsThe most discriminating tests at baseline were measures of acquisition, delayed recall, and associative memory, followed by everyday memory, and spatial memory tasks, with MCI patients scoring significantly lower than controls. At follow-up (mean time elapsed: 22.4 months), 6 MCI cases had progressed to clinically probable AD. Exploratory logistic regression analyses revealed that delayed associative memory performance at baseline was a potential predictor of subsequent conversion to AD.ConclusionsAs a preliminary study, our findings suggest that simple associative memory paradigms with real-world relevance represent an important line of enquiry in future longitudinal studies charting MCI progression over time.

Highlights

Decline in episodic memory is one of the hallmark features of Alzheimer’s disease (AD) and is a defining feature of amnestic Mild Cognitive Impairment (MCI), which is posited as a potential prodrome of AD
Progression from MCI to AD At follow-up, 6 of the 16 MCI participants (37.5%) had converted to probable AD (MCIc), and 1 case was diagnosed with behavioural-variant frontotemporal dementia, with the remaining 9 participants representing stable MCI (MCIs)
Two participants showed an increase in MMSE scores at follow-up; this was not sufficient to denote a return to healthy cognitive functioning, as evidenced by persistent cognitive deficits, with neuropsychological test scores falling below 1.5 standard deviations of ageadjusted norms

Summary

Introduction

Decline in episodic memory is one of the hallmark features of Alzheimer’s disease (AD) and is a defining feature of amnestic Mild Cognitive Impairment (MCI), which is posited as a potential prodrome of AD. FaceName associative tasks represent an interesting analogue of the associative encoding individuals are faced with in daily life, and the formation of cross-modal associations between inherently unrelated items of information is likely to be hippocampal-dependent [11] This branch of associative memory appears to be compromised in the earliest stages of AD whereas mixed results have been obtained for MCI individuals [11]. Neuroimaging studies have shown marked reduction in hippocampal and entorhinal cortex volumes in MCI [12], with such pathology at a transitional level to normal aging and AD [13] These medial temporal lobe regions are typically involved in episodic memory [11] with a central role ascribed to the hippocampus for relational or associative memory [14,15].

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