Cognitive control and memory in healthy ApoE-ε4 carriers with a family history of Alzheimer’s disease.

Abstract

A major risk factor for late-onset Alzheimer’s type dementia (DAT) is the carriage of the ε4 allele of the apolipoprotein E (ApoE) gene. Identifying cognitive deficits in healthy ApoE-ε4 carriers is valuable in order to develop interventions to prevent them from developing DAT. Existing evidence about cognitive deficits in the domains of episodic memory and cognitive control specific to ApoE-ε4 is contradictory. The objective of our research was to assess episodic memory and cognitive control in healthy ApoE-ε4 carriers. Cognitively healthy ApoE-ε4 carriers (13 ε4/ε4 heterozygotes) and noncarriers (22 ε3/ε3 homozygotes), who were matched on age and family history of DAT, were compared on episodic-memory and cognitive-control tasks. Episodic-memory tasks were verbal and visual recognition tasks with a systematic variation of distractor-to-target similarity. Executive functions were assessed by a task for updating working memory, an inhibition task, and a switching task. Working-memory capacity was also assessed. The results showed that executive functions were generally not impaired in the carriers, but carriers showed a specific increase in accuracy-related switch costs. Workingmemory capacity was not reduced in the carriers. In the domain of episodic memory, the carriers were found to make more errors with phonetic distractors in the verbal episodicmemory task. They also tended to make more errors with visually dissimilar distractors in the visual episodic-memory task. The results are indicative of an episodic-memory deficit specific to the carriage of ApoE-ε4. This deficit may be driven either by deficits in storage or by deficits in the encoding of the to-be-remembered material. Contradictory results concerning the presence of an episodic-memory deficit obtained in previous studies may stem from small effect sizes, the use of specific materials, and the employment of attention-intensive encoding strategies. The carriers also showed a switching deficit that possibly is related to difficulty in retrieving task rules from episodic memory. Existing empirical contradictions concerning the presence of an executive deficit in carriers may in part depend on the extent to which tasks used to assess an executive deficit draw on the switching function. In this study, there was no general executive deficit in the carriers of ApoE-ε4.

Keywords

• apolipoprotein E
• Alzheimer’s type dementia
• episodic memory
• cognitive control
• executive functions
• working memory
• attention
• task switching