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. 2012 Apr 10;78(15):1116-22.
doi: 10.1212/WNL.0b013e31824f7ff2. Epub 2012 Apr 4.

Terminal dedifferentiation of cognitive abilities

R S Wilson  1 , E Segawa, L P Hizel, P A Boyle, D A Bennett
Affiliations

Terminal dedifferentiation of cognitive abilities

R S Wilson et al. Neurology. .

Abstract

Objective: To test the cognitive dedifferentiation hypothesis that cognitive abilities become increasingly correlated in late life.

Methods: Participants are 174 older persons without dementia at the beginning of a longitudinal clinical-pathologic cohort study. At annual intervals for 6 to 15 years prior to death, they completed a battery of cognitive performance tests from which previously established composite measures of episodic memory, semantic memory, working memory, and perceptual speed were derived. At death, there was a uniform neuropathologic assessment and levels of diffuse plaques, neuritic plaques, and neurofibrillary tangles were summarized in a composite measure. Change in the 4 cognitive outcomes was analyzed simultaneously in a mixed-effects model that allowed rate of decline to accelerate at a variable point before death.

Results: On average, cognitive decline before the terminal period was relatively gradual, and rates of change in different cognitive domains were moderately correlated, ranging from 0.25 (episodic memory-working memory) to 0.46 (episodic memory-semantic memory). By contrast, cognition declined rapidly during the terminal period, and rates of change in different cognitive functions were strongly correlated, ranging from 0.83 (working memory-perceptual speed) to 0.89 (episodic memory-semantic memory, semantic memory-working memory). Higher level of plaques and tangles on postmortem examination was associated with faster preterminal decline and earlier onset of terminal decline but not with rate of terminal decline or correlations between rates of change in different cognitive functions.

Conclusion: In the last years of life, covariation among cognitive abilities sharply increases consistent with the cognitive dedifferentiation hypothesis.

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Figures

Figure 1
Figure 1. Typical paths of change in different cognitive domains
Predicted paths of change in different cognitive domains for a typical participant who died after 10 years in the study, adjusted for age at death, sex, and education.
Figure 2
Figure 2. Correlation between change in different cognitive domains
Scatterplots of the association between rates of cognitive change in different cognitive domains before the terminal period (left side) and during it (right side), adjusted for age at death, sex, and education.
See this image and copyright information in PMC

Comment in

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