Abstract and Introduction
Abstract
The authors examined the associations of participants' and their parents' educational levels with cognitive decline while addressing methodological limitations that might explain inconsistent results in prior work. Residents of Dijon, France (n = 4,480) 65 years of age or older who were enrolled between 1999 and 2001 were assessed using the Isaacs' verbal fluency test, Benton Visual Retention Test, Trail Making Test B, and Mini-Mental State Examination up to 5 times over 9 years. The authors used random-intercepts mixed models with inverse probability weighting to account for differential survival (conditional on past performance) and quantile regressions to assess bias from measurement floors or ceilings. Higher parental educational levels predicted better average baseline performances for all tests but a faster average decline in score on the Isaacs' test. Higher participant educational attainment predicted better baseline performances on all tests and slower average declines in Benton Visual Retention Test, Trail Making Test B, and Mini-Mental State Examination scores. Slope differences were generally small, and most were not robust to alternative model specifications. Quantile regressions suggested that ceiling effects might have modestly biased effect estimates, although the direction of this bias might depend on the test instrument. These findings suggest that the possible impacts of educational experiences on cognitive change are small, domain-specific, and potentially incorrectly estimated in conventional analyses because of measurement ceilings.
Introduction
Prior research has suggested that both a person's own educational attainment or duration of schooling and that of his/her parents affect the risk of cognitive impairment and dementia in the later years. There has been little research on the association between parental educational level and the rate of cognitive decline, however, and findings regarding one's own education and cognitive change have been mixed. Results from several early studies suggested that education slowed the rate of cognitive decline, which was consistent with the theory of cognitive reserve. However, these results were challenged by subsequent reports in which improved longitudinal methods were used. Some recent analyses found that individuals with higher levels of education or socioeconomic position experience accelerated cognitive decline, at least in some domains or age groups. Although this surprising result has been largely regarded as spurious, we consider 3 possible explanations for the association.
First, education might predict accelerated cognitive aging if cognitive skills developed through education are early targets of neurodegenerative or cerebrovascular disease. For example, individuals with high levels of education are more likely to deploy explicit strategies in verbal fluency and verbal memory tests. These strategies are associated with recruitment of specific cortical regions, for example, the dorsolateral prefrontal cortex. Cortical networks or regions underlying strategy use may be affected relatively early in the development of neurodegenerative diseases. If so, highly educated individuals may be differentially affected and decline more quickly than others, especially in strategy-dependent domains.
Second, education might predict accelerated cognitive decline under a "last in, first out" model, in which more recently developed cognitive skills are lost earliest as age-related neurologic disease develops. This explanation suggests that factors that influence cognitive skills early in life, for example, parental education, would be less strongly associated with cognitive decline than factors affecting later cognitive development, such as one's own education.
Finally, although education is generally considered salubrious, it could increase the risk of neurologic disease via behavioral or physiologic changes. This seems unlikely given prior evidence about the health effects of education, but it cannot be ruled out. We examined relations between one's own and parental education and the rates of decline in 4 domains of cognitive function in a French cohort, using methods to help address methodological limitations that might explain inconsistent results in prior work.