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Do clever brains age more slowly? Further exploration of a nun result.

Article Excerpt
It is important to discover factors that predict mental competence in old age because these may identify the functional processes that cause cognitive loss, suggest measures that may help more of us to retain our abilities to the ends of our lives, and serve as markers for appropriate interventions. A recent finding, welcomed by the more self. confident among our older academic colleagues, suggests that people who have higher levels of mental ability as young adults may retain their competence longer into old age. In a uniquely well-controlled study, measures of the idea density and grammatical complexity of autobiographical notes written by 93 nuns when they were young novices were found directly to predict their subsequent longevity and maintenance of intellectual competence in old age, and inversely to predict their risk of suffering from Alzheimer's disease (Snowden et al., 1996). It is noteworthy that these measures of idea density and syntactic complexity are not only indices of vocabulary and linguisti c ability but are also good proxies for scores on tests of general fluid intelligence.

Between writing their autobiographical notes and being assessed in old age, most of the nuns in the Snowden et al. (1996) study lived out long lives in almost identical stable environments. This key advantage of a unique dataset equates for factors such as nutrition, housing, access to health care, occupational risks, and exposure to toxicity that are also associated with higher intellectual competence and longer survival (Snowden, Ostwald, Kane, & Keenan, 1989). Further, since all nuns were thoroughly documented throughout their convent lives, the effects of pathologies and biological life events could also be taken into consideration (Houx, Vreeling, & Jolles, 1991).

A contrary argument is that demographic and health factors that operate in infancy and childhood are also known to increase both intellectual competence and longevity. Children in socio-economically advantaged families tend to have a higher birth weight, better nutrition, and better health in infancy and childhood. These latter factors also significantly reduce mortality and promote both young adult-level and long-term maintenance of intellectual competence (Leon, 1998; Sorensenson, 1997). These factors may have determined the nuns' futures long before they wrote their autobiographical notes.

Data accumulated during a longitudinal study of a large population (Rabbitt, Donlan, Bent, McInnes, & Abson, 1993) offered a different way to test the relationship between level of youthful ability and amount of cognitive decline in old age. The validity of intelligence tests is widely debated, but people's scores on tests of fluid general mental abilities, such as the Helm AH 4 (1) test (Heim, 1970), are still among the best available empirical predictors of their competence at a wide range of other intellectual tasks, their success at academic and other careers, and even of their efficiency on simple tests of decision speed and memory (Anderson, 1995; Jensen, 1980; Jensen & Whang, 1993; Vernon, 1983).

Young adults' scores on vocabulary tests such as the Raven (1965) Mill Hill A test closely predict their scores on tests of fluid general intellectual abilities. As people grow old, their scores on intelligence tests decline, but their scores on vocabulary tests remain constant or may even...