Journal of the International Neuropsychological Society



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


DAVID  SCHRETLEN a1c1, GODFREY D.  PEARLSON a1, JAMES C.  ANTHONY a2, ELIZABETH H.  AYLWARD a1a3, ANN M.  AUGUSTINE a1, AMANDA  DAVIS a1 and PATRICK  BARTA a1
a1 Department of Psychiatry and Behavioral Science, Johns Hopkins University School of Medicine
a2 Department of Mental Hygiene, Johns Hopkins University School of Hygiene and Public Health
a3 Department of Radiology, University of Washington School of Medicine

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.)

(Received November 4 1998)
(Revised February 1 1999)
(Accepted February 23 1999)


Key Words: Cognitive aging; Brain MRI; Fluid intelligence; Frontal lobe; Executive ability; Working memory.

Correspondence:
c1 Reprint requests to: David Schretlen, Johns Hopkins Hospital, 600 N. Wolfe Street, Meyer 218, Baltimore, MD 21287-7218. E-mail: dschret@jhmi.edu