title: Terminal dedifferentiation of cognitive abilities.
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.
  
  
  CONCLUSIONS
  In the last years of life, covariation among cognitive abilities sharply increases consistent with the cognitive dedifferentiation hypothesis.
authors.affiliation: Rush Alzheimer’s Disease Center and Department of Neurological Sciences, Rush University Medical Center, Chicago, IL, USA. rwilson@rush.edu
authors.forename: R S
authors.initials: RS
authors.lastname: Wilson
authors.forename: E
authors.initials: E
authors.lastname: Segawa
authors.forename: L P
authors.initials: LP
authors.lastname: Hizel
authors.forename: P A
authors.initials: PA
authors.lastname: Boyle
authors.forename: D A
authors.initials: DA
authors.lastname: Bennett
mesh_terms: D000544:Alzheimer Disease / Q000473:pathology / Q000523:psychology; D001921:Brain / Q000473:pathology*; D003071:Cognition; D003072:Cognition Disorders / Q000453:epidemiology / Q000473:pathology* / Q000523:psychology*; D060825:Cognitive Dysfunction / Q000473:pathology / Q000523:psychology; D015986:Confounding Factors, Epidemiologic; D004522:Educational Status; D006801:Humans; D015233:Models, Statistical; D016874:Neurofibrillary Tangles / Q000473:pathology; D009483:Neuropsychological Tests; D058225:Plaque, Amyloid / Q000473:pathology; D019452:Terminally Ill / Q000523:psychology / Q000706:statistics & numerical data; D014481:United States / Q000453:epidemiology