Elucidating the contributions of processing speed, executive ability, and frontal lobe volume to normal age-related differences in fluid intelligence

Abstract

One theory of normal cognitive aging asserts that decreases in simple processing speed mediate the age-related decline of fluid intelligence. Another possibility is that age-related atrophic changes in frontal brain structures undermine the functioning of executive abilities, thereby producing the same decline. In this study, we used principal components analysis to derive a measure of fluid-spatial intelligence in 197 normal adults between 20 and 92 years of age. Measures of perceptual comparison speed, working memory, and executive ability, as well as regional brain volumes based on high resolution magnetic resonance imaging were obtained from a subsample of 112 participants. We then conducted a series of hierarchical multiple regression analyses to test whether (1) the processing speed theory, (2) frontal-executive theory, or (3) some combination of these best accounted for age-related variation in fluid intelligence. The results showed that perceptual comparison speed, executive ability, and frontal lobe volume each made significant contributions to a regression equation that explained 57% of the variance in fluid intelligence. These findings suggest that both the processing speed and frontal-executive theory of cognitive aging are partially correct and complement one another. (JINS, 2000, 6, 52-61.)

Demographic Influences on Baseline and Derived Scores From the Trail Making Test in Healthy Older Australian Adults

“…However, it would appear that the influence was limited to psychomotor speed, as only TMT-A performance was significantly predicted by gender. In addition, our results indicated that TMT-B was influenced by a small but significant effect of education, which is consistent with the more general effect of this variable on executive function (Daigneault & Braun, 1993;Fisk & Warr, 1996;Keys & White, 2000;Schretlen et al, 2000;Van der Linden, Beerten, & Pesenti, 1998;West, 2001). The influence of education was of particular interest due to the relative absence of education-adjusted normative data in the literature.…”

Cortical thickness is linked to executive functioning in adulthood and aging

“…Specifically, greater anterior cingulate volume was associated with less time needed to complete the Stroop Inhibition Task, whereas larger orbitofrontal volumes were associated with poorer verbal fluency. Other studies show that, in older adults, smaller PFC gray-matter volume [Gunning-Dixon and Raz, 2003] and smaller right frontal-lobe volume [Hanninen et al, 1997] were related to a higher number of perseverative errors in the WCST, and that larger frontal-lobe volume was positively linked to the number of completed WCST categories [Schretlen et al, 2000].…”

Socioeconomic status is positively correlated with frontal white matter integrity in aging

“…The CCF (scale 3) consists of 50 items and assesses inductive reasoning through the ability to perceive relationships in shapes and figures. Age-adjusted IQ scores were used because fluid intelligence has been shown to decline with age (Schretlen et al 2000). The two groups did not differ in mean IQ (young adult group: M=120.2, SD=19.7; senior group: M= 123.8, SD=21.1) [t(82)=−0.804, P<0.424].…”