Elsevier

Neurobiology of Aging

Volume 30, Issue 4, April 2009, Pages 507-514
Neurobiology of Aging

Open peer commentary manuscript
When does age-related cognitive decline begin?

https://doi.org/10.1016/j.neurobiolaging.2008.09.023Get rights and content

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.

Section snippets

Sample

Characteristics of the samples of participants are summarized in Table 1. The research participants were recruited from newspaper advertisements, flyers, and referrals from other participants, and all were tested individually. The cross-sectional sample included the first assessment from the participants in the samples with longitudinal and short-term retest data, plus additional participants from other studies (Salthouse, 2004, Salthouse, 2005). All research participants were between 18 and 60

Results

All of the cognitive variables were converted to z-scores by subtracting the score from the total sample mean at the first assessment, and dividing the difference by the standard deviation (S.D.). Fig. 2 portrays the cross-sectional age trends for the 12 variables, where it can be seen that every variable had a linear relation with age. Three variables, matrix reasoning, form boards, and pattern comparison, also had significant quadratic trends, but in each case the quadratic trend was

Discussion

Fig. 2 reveals that there were significant negative relations between age and several different types of cognitive measures for healthy educated adults ranging from 18 to 60 years of age. Furthermore, additional analyses revealed that the age relations were not attributable to a variety of plausible confounding variables. These results, together with similar findings in many other studies, clearly establish the existence of cross-sectional age-related declines for many cognitive variables prior

Conflict of interest statement

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

Acknowledgements

Supported by Grant R37AG024270 from the National Institute on Aging.

Institutional Review Board approval: The research described in this report was conducted with approval of the Institutional Review Board at The University of Virginia.

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