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. 2009 Apr;30(4):507-14.
doi: 10.1016/j.neurobiolaging.2008.09.023. Epub 2009 Feb 20.

When does age-related cognitive decline begin?

Timothy A Salthouse  1
Affiliations

When does age-related cognitive decline begin?

Timothy A Salthouse. Neurobiol Aging. 2009 Apr.

Abstract

Cross-sectional comparisons have consistently revealed that increased age is associated with lower levels of cognitive performance, even in the range from 18 to 60 years of age. However, the validity of cross-sectional comparisons of cognitive functioning in young and middle-aged adults has been questioned because of the discrepant age trends found in longitudinal and cross-sectional analyses. The results of the current project suggest that a major factor contributing to the discrepancy is the masking of age-related declines in longitudinal comparisons by large positive effects associated with prior test experience. Results from three methods of estimating retest effects in this project, together with results from studies comparing non-human animals raised in constant environments and from studies examining neurobiological variables not susceptible to retest effects, converge on a conclusion that some aspects of age-related cognitive decline begin in healthy educated adults when they are in their 20s and 30s.

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Conflict of interest statement

Disclosure Statement: The author has no financial or other conflicts related to this research.

Figures

Figure 1
Figure 1
Estimates of cross-sectional differences and longitudinal changes over 7 years in two variables from the Seattle Longitudinal Study. Cross-sectional data from Table 4.2 and longitudinal data from Table 5.1 of Schaie (2005). The figures in the top two panels portray results of cross-sectional (dotted lines) and longitudinal (solid lines) comparisons in T-score units. The figures in the bottom two panels portray the same data as differences or changes over a 2.5 year interval in standard deviation units.
Figure 2
Figure 2
Means and standard errors for 12 cognitive variables by 5-year age intervals. The variables are grouped according to the type of cognitive ability as determined by confirmatory factor analyses.
Figure 3
Figure 3
Estimates of cross-sectional differences and longitudinal changes over 2.5 years, of the short-term retest effect, and of retest effects derived from two analytical methods for 12 cognitive variables. The vertical axis is in standard deviation units.
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