Episodic autobiographical memory in amnestic mild cognitive impairment: what are the neural correlates?

Abstract

Autobiographical memory in amnestic Mild Cognitive Impairment (aMCI) is characterized by impaired retrieval of episodic memories, but relatively preserved personal semantic knowledge. This study aimed to identify (via FDG-PET) the neural substrates of impaired episodic specificity of autobiographical memories in 35 aMCI patients compared with 24 healthy elderly controls. Significant correlations between regional cerebral activity and the proportion of episodic details in autobiographical memories from two life periods were found in specific regions of an autobiographical brain network. In aMCI patients, more than in controls, specifically episodic memories from early adulthood were associated with metabolic activity in the cuneus and in parietal regions. We hypothesized that variable retrieval of episodic autobiographical memories in our aMCI patients would be related to their variable capacity to reactivate specific sensory-perceptual and contextual details of early adulthood events linked to reduced (occipito-parietal) visual imagery and less efficient (parietal) attentional processes. For recent memories (last year), a correlation emerged between the proportion of episodic details and activity in lateral temporal regions and the temporo-parietal junction. Accordingly, variable episodic memory for recent events may be related to the efficiency of controlled search through general events likely to provide cues for the retrieval of episodic details and to the ability to establish a self perspective favouring recollection.

Keywords: attention; autobiographical memory; episodic memory; mild cognitive impairment; neuroimaging; self.

Figure 1

Number of internal and external details contained in autobiographical memories narrated by aMCI patients and healthy controls either spontaneously (A) or after general probing (B) for both time periods.

Figure 2

Proportion of internal details in the production of autobiographical memories by patients with aMCI and control participants.

Figure 3

Results of the SPM analyses showing metabolic regional activity significantly correlated (P < 0.001 uncorrected) with the proportion of internal details during spontaneous recall and after general probing in the two time periods in aMCI patients (contrast: aMCI > controls, with inclusive masking by aMCI at P < 0.05) rendered on a single subject brain.