Normal Aging and Executive Functions in “Old-Old” Community Dwellers: Poor Performance Is Not an Inevitable Outcome
|Olivier Piguet a1a2, David A. Grayson a3, G. Anthony Broe a2, Robyn L. Tate a4, Hayley P. Bennett a2, Tanya C. Lye a1, Helen Creasey a1 and Lloyd Ridley a5|
a1 Centre for Education & Research on Ageing at Concord Repatriation General Hospital, The University of Sydney, Sydney, Australia
a2 Prince of Wales Medical Research Institute, Randwick, Australia
a3 Department of Psychology, The University of Sydney, Sydney, Australia
a4 Rehabilitation Studies Unit, Department of Medicine, The University of Sydney, Sydney, Australia
a5 Department of Radiology, Concord Repatriation General Hospital, Concord, Australia
Background: Studies on normal aging and cognitive functioning commonly describe early and more pronounced age-related changes in executive functions (EFs) compared to other cognitive abilities. Two of the three most common neurodegenerative disorders associated with aging (vascular dementia [VaD] and extrapyramidal [EP]-related dementia) show executive dysfunctions in their clinical presentation; and these cognitive deficits are not uncommon in the third one: Alzheimer's disease (AD). Methods: Nine EF tests (yielding 12 measures) were administered to 123 randomly selected community dwellers, aged 81 years and over, with the view to determine the effect of age on performance. Markers of AD, VaD, and EP-related dementia, as well as sociodemographic and psychological variables, were selected and their contribution to EF performance was investigated. Results: Multiple linear regression analyses revealed the greatest contribution to EF scores from the markers of AD and estimated IQ but not from the markers of VaD and EP-related dementia or from age. Conclusions: These findings suggest that chronological age acts as a proxy variable mediating the impact of other factors such as subclinical signs of neurodegenerative disorders and that it has little independent contribution to make. They also indicate the importance of cognitive abilities supported by posterior cortical circuits in EF problem resolution. This study demonstrates that cognitive decline is not an ineluctable process that is associated with “normal” aging but rather represents, in many cases, a byproduct of neurodegenerative disorders, albeit themselves highly age-related.
Key Words: Normal aging; dementia; cognition; executive functions; 80 years and over.