Cognitive profiles in dementia: Alzheimer disease vs healthy brain aging

Abstract

Objective: To re-examine proposed models of cognitive test performance that concluded separate factor structures were required for people with Alzheimer disease (AD) and older adults without dementia.

Methods: Five models of cognitive test performance were compared using multistep confirmatory factor analysis in 115 individuals with autopsy-confirmed AD and 191 research participants without clinical dementia from longitudinal studies at the Washington University AD Research Center. The models were then cross-validated using independent samples of 323 people with clinically diagnosed dementia of the Alzheimer type and 212 cognitively healthy older adults.

Results: After controlling for Alzheimer-specific changes in episodic memory, performance on the battery of tests used here was best represented in people both with and without dementia by a single model of one general factor and three specific factors (verbal memory, visuospatial ability, and working memory). Performance by people with dementia was lower on the general factor than it was by those without dementia. Larger variances associated with the specific factors in the group with dementia indicated greater individual differences in the pattern of cognitive deficits in the stage of AD.

Conclusions: A hybrid model of general and specific cognitive domains simplifies cognitive research by allowing direct comparison of normal aging and Alzheimer disease performance. The presence of a general factor maximizes detection of the dementia, whereas the specific factors reveal the heterogeneity of dementia's associated cognitive deficits.

Figure 1 Relative fit of four candidate hypothetical models Models were tested with confirmatory factor analyses based on previous studies was examined to determine domain content, factor loadings, and factor interrelationships. Model D was found to best describe cognitive abilities in samples with and without dementia. See text for complete details. INFO = information; PA = Paired Associate Learning; BNT = Boston Naming Test; LM = Logical Memory; BVRT = Benton Visual Retention Test; DSym = Digit Symbol; TRA = Trailmaking A; BD = Block Design; WF = Word Fluency; MC = Mental Control; DS-B = Digit Span Backward; DS-F = Digit Span Forward.

Figure 2 Results of between-group tests of invariance (TOI) to compare independent samples (A) Confirmatory factor analysis (CFA) model of cognitive performance in older adults without dementia (sample 1). (B) Slight modification of the CFA model of cognitive performance in individuals with mild Alzheimer disease (autopsy confirmed sample) by allowing the errors in Logical Memory and Associate Learning to correlate. Loadings are identical across figures. INFO = information; PA = Paired Associate Learning; BNT = Boston Naming Test; LM = Logical Memory; BVRT = Benton Visual Retention Test; DSym = Digit Symbol; TRA = Trailmaking A; BD = Block Design; WF = Word Fluency; MC = Mental Control; DS-B = Digit Span Backward; DS-F = Digit Span Forward.