Episodic, but not semantic, autobiographical memory is reduced in amnestic mild cognitive impairment

Abstract

Amnestic mild cognitive impairment (aMCI) is characterized by decline in anterograde memory as measured by the ability to learn and remember new information. We investigated whether retrograde memory for autobiographical information was affected by aMCI. Eighteen control (age 66-84 years) and 17 aMCI (age 66-84 years) participants described a personal event from each of the five periods across the lifespan. These events were transcribed and scored according to procedures that separate episodic (specific happenings) from semantic (general knowledge) elements of autobiographical memory. Although both groups generated protocols of similar length, the composition of autobiographical recall differentiated the groups. The aMCI group protocols were characterized by reduced episodic and increased semantic information relative to the control group. Both groups showed a similar pattern of recall across time periods, with no evidence that the aMCI group had more difficulty recalling recent, rather than remote, life events. These results indicate that episodic and semantic autobiographical memories are differentially affected by the early brain changes associated with aMCI. Reduced autobiographical episodic memories in aMCI may be the result of medial temporal lobe dysfunction, consistent with multiple trace theory, or alternatively, could be related to dysfunction of a wider related network of neocortical structures. In contrast, the preservation of autobiographical semantic memories in aMCI suggests neural systems, such as lateral temporal cortex, that support these memories, may remain relatively intact.

Figures

Figure 1

The number of details generated during autobiographical recall, for each life period according to (A) internal and (B) external detail categories. There is no group difference in the total number of details generated, but there is a significant group-by-detail-category interaction. Controls generate more internal details and aMCI participants more external details when recollecting personal events. Error bars represent 95% confidence intervals. aMCI = amnestic mild cognitive impairment.

Figure 2

Categorization of details comprising autobiographical memories, with the number of details averaged across the five life periods, for each participant group. (A) Internal details representing episodic information. The event subcategory represents the majority of the output. (B) External details are comprised primarily of semantic information, with the semantic subcategory representing the majority of the output. There is also a significant group-by-external-detail-type interaction whereby semantic details are significantly elevated in the aMCI group as compared to the control group. Error bars represent 95% confidence intervals. Percep. = Perceptions, Em/Th = Emotion / Thought, Ex. Event = External Event, and aMCI = amnestic mild cognitive impairment.

Figure 3

The ratio of internal-to-total number of details generated, representing an index of episodic re-experiencing in autobiographical recall, shows no clear temporal gradient and is greater in the control as compared to the aMCI group. Error bars represent 95% confidence intervals. aMCI = amnestic mild cognitive impairment.