Effects of cognitive reserve depend on executive and semantic demands of the task

Abstract

Background: Cognitive reserve (CR) is one factor that helps to maintain cognitive function in patients with Alzheimer's disease (AD). Whether the effects of CR depend on the semantic/executive components of the task remains unknown.

Methods: 470 patients (138 with AD, 332 with mild cognitive impairment (MCI)) were selected from the Alzheimer's Disease Neuroimaging Initiative database. Linear regression models were used to determine the effects of CR (years of education) on cognitive performance after controlling for demographic factors and regional cortical atrophy. First, we assessed memory tasks with low (Auditory Verbal Learning Test (AVLT) discriminability), moderate (AVLT delayed recall) and high (Logical Memory Test (LMT) delayed recall) executive/semantic components. Next, we assessed tasks with lower (digit span forward, Trails A) or higher (digit span backwards, Trails B) executive demands, and lower (figure copying) or higher (naming, semantic fluency) semantic demands.

Results: High CR was significantly associated with performance on the LMT delayed recall, approached significance in the AVLT delayed recall and was not significantly associated with performance on AVLT discriminability. High CR was significantly associated with performance on the Trails B and digit span backwards, mildly associated with Trails A performance and was not associated with performance on digit span forwards. High CR was associated with performance on semantic but not visuospatial tasks. High CR was associated with semantic tasks in patients with both MCI and AD, but was only associated with executive functions in patients with MCI.

Conclusion: CR may relate to executive functioning and semantic knowledge, leading to preserved cognitive performance in patients with AD pathology.

Keywords: Alzheimer’s disease; Cognitive reserve; Mild cognitive impairment; executive functioning; neural compensation.

Figure 1

Hierarchical linear regression model and predictions. Cognitive task performance is first controlled for age, gender and regional cortical atrophy. Next, the effects of cognitive reserve (CR) on task performance are plotted on the graph (y-axis) in relation to CR (x-axis). We predict that CR will not modulate cognitive performance on tasks with lower executive/semantic demands, but will improve cognitive performance on tasks with higher executive/semantic demands.

Figure 2

Cognitive reserve (CR) improves memory performance on tasks with high executive/semantic components. Relationship between standardised Z-scores of test performance (controlled for age, gender and regional cortical atrophy) and CR (years of education) for memory tasks with low (A), moderate (B) or high (C) executive/semantic demands. AVLT, Auditory Verbal Learning Test; LMT, Logical Memory Test.

Figure 3

Cognitive reserve (CR) improves performance on tasks with high executive component. Relationship between standardised Z-scores of test performance (controlled for age, gender and regional cortical atrophy) and CR (years of education) for tasks with high (A,B) versus low (C,D) executive component.

Figure 4

Cognitive reserve (CR) improves performance on tasks with high semantic component. Relationship between standardised Z-scores of test performance (controlled for age, gender and regional cortical atrophy) and CR (years of education) for tasks with high (A,B) versus low (C) semantic component.