title: Idea density measured in late life predicts subsequent cognitive trajectories: implications for the measurement of cognitive reserve.
abstract: OBJECTIVE
  The Nun Study showed that lower linguistic ability in young adulthood, measured by idea density (ID), increased the risk of dementia in late life. The present study examined whether ID measured in late life continues to predict the trajectory of cognitive change.
  
  
  METHODS
  ID was measured in 81 older adults who were followed longitudinally for an average of 4.3 years. Changes in global cognition and 4 specific neuropsychological domains (episodic memory, semantic memory, spatial abilities, and executive function) were examined as outcomes. Separate random effects models tested the effect of ID on longitudinal change in outcomes, adjusted for age and education.
  
  
  RESULTS
  Lower ID was associated with greater subsequent decline in global cognition, semantic memory, episodic memory, and spatial abilities. When analysis was restricted to only participants without dementia at the time ID was collected, results were similar.
  
  
  CONCLUSIONS
  Linguistic ability in young adulthood, as measured by ID, has been previously proposed as an index of neurocognitive development and/or cognitive reserve. The present study provides evidence that even when ID is measured in old age, it continues to be associated with subsequent cognitive decline and as such may continue to provide a marker of cognitive reserve.
authors.affiliation: Department of Neurology, University of California, Davis, CA 95817, USA. sarah.farias@ucdmc.ucdavis.edu
authors.forename: Sarah Tomaszewski
authors.initials: ST
authors.lastname: Farias
authors.forename: Vineeta
authors.initials: V
authors.lastname: Chand
authors.forename: Lisa
authors.initials: L
authors.lastname: Bonnici
authors.forename: Kathleen
authors.initials: K
authors.lastname: Baynes
authors.forename: Danielle
authors.initials: D
authors.lastname: Harvey
authors.forename: Dan
authors.initials: D
authors.lastname: Mungas
authors.forename: Christa
authors.initials: C
authors.lastname: Simon
authors.forename: Bruce
authors.initials: B
authors.lastname: Reed
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D003072:Cognition Disorders / Q000150:complications / Q000503:physiopathology*; D058245:Cognitive Reserve; D032882:Comprehension; D003704:Dementia / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008569:Memory Disorders / Q000503:physiopathology; D008603:Mental Health / Q000706:statistics & numerical data*; D008875:Middle Aged; D012720:Severity of Illness Index; D012959:Socioeconomic Factors