Episodic vs. Autobiographical Memory in Patients with Amnestic Mild Cognitive Impairment (aMCI): Are they Different Systems?

Is there a difference between autobiographical memory and episodic memory? Are they identical, as some researchers have treated them, or is autobiographical memory “a superordinate system with episodic memory as a subsystem,” as claimed by this article by Martin Conway, which holds that “Episodic memory is reconceived as a memory system that retains highly detailed sensory perceptual knowledge of recent experience over retention intervals measured in minutes and hours. Episodic knowledge has yet to be integrated with the autobiographical memory knowledge base and so takes as its context or referent the immediate past of the experiencing self (or the ‘I’). When recalled, it can be accessed independently of content and is recollectively experienced. Autobiographical memory, in contrast, retains knowledge over retention intervals measured in weeks, months, years, decades, and across the life span. Autobiographical knowledge represents the experienced self (or the ‘me’), is always accessed by its content and, when accessed, does not necessarily give rise to recollective experience. Instead, recollective experience occurs when autobiographical knowledge retains access to associated episodic memories. In this reworking of the ‘episodic memory’ concept autobiographical memory provides the instantiating context for sensory—perceptual episodic memory.”

If these two memory systems are identical, claimed Silke Matura, Laboratory for Neurophysiology and Neuroimaging, Department of Psychiatry, University Clinic, Frankfurt am Mein, and colleagues in a poster presented at ICAD 2009, then “aMCI patients should also show impaired recall of personal lifetime events.”

To determine whether this is the case, the researchers investigated autobiographical and episodic memory “on a behavioral level,” looking for “morphological alterations in neuronal structures associated with episodic and autobiographical memory” using voxel-based morphometry (VBM).

The authors studied 12 patients with aMCI (average age 68.2 years, average education of 13.4 years, and mean MMSE score of 29.3) and 13 controls. Subjects were administered the CERAD Clinical and Neuropsychology Assessment to “capture episodic memory dysfunction.” Subjects also participated in semi-structured interviews (using the Bielefelder Autobiographical Memory Inventory, known as BAGI) prior to screening, and were asked to recall recent memories as well as those from their early childhood, late childhood, adolescence, and early adulthood. The authors also analyzed subjects’ MRI data with VBM under SPM%, using the VBM5 toolbox developed by Christian Gaser.

They reported that “there were no significant differences in the [BAGI] Episodic Index among aMCI patients and controls.” However, they reported that analysis of the CERAD results indicated that aMCI patients differed significantly from the controls in terms of their recall performance. VBM results revealed that aMCI patients “showed a widespread pattern of reduced grey matter concentration,” and that “performance in episodic memory task was correlated with atrophy in the right hippocampus in the aMCI group.” The authors found no correlation between brain atrophy and performance in autobiographical memory recall. These findings, they concluded, suggest that episodic and autobiographical memory are not identical systems.