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IQ as Moderator of Terminal Decline in Perceptual and Motor Speed, Spatial, and Verbal Ability: Testing the Cognitive Reserve Hypothesis in a Population-Based Sample Followed From Age 70 Until Death

Journal article
Authors Valgeir Thorvaldsson
Ingmar Skoog
Boo Johansson
Published in Psychology and Aging
Volume 32
Issue 2
Pages 148-157
ISSN 0882-7974
Publication year 2017
Published at Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry
Department of Psychology
Centre for Ageing and Health (Agecap)
Pages 148-157
Language en
Keywords terminal decline; cognition; cognitive reserve; IQ
Subject categories Gerontology, specializing in Medical and Health Sciences, Psychology


Terminal decline (TD) refers to acceleration in within-person cognitive decline prior to death. The cognitive reserve hypothesis postulates that individuals with higher IQ are able to better tolerate age-related increase in brain pathologies. On average, they will exhibit a later onset of TD, but once they start to decline, their trajectory is steeper relative to those with lower IQ. We tested these predictions using data from initially nondemented individuals (n = 179) in the H70-study repeatedly measured at ages 70, 75, 79, 81, 85, 88, 90, 92, 95, 97, 99, and 100, or until death, on cognitive tests of perceptual-and-motor-speed and spatial and verbal ability. We quantified IQ using the Raven’s Coloured Progressive Matrices (RCPM) test administrated at age 70. We fitted random change point TD models to the data, within a Bayesian framework, conditioned on IQ, age of death, education, and sex. In line with predictions, we found that 1 additional standard deviation on the IQ scale was associated with a delay in onset of TD by 1.87 (95% highest density interval [HDI; 0.20, 4.08]) years on speed, 1.96 (95% HDI [0.15, 3.54]) years on verbal ability, but only 0.88 (95% HDI [−0.93, 3.49]) year on spatial ability. Higher IQ was associated with steeper rate of decline within the TD phase on measures of speed and verbal ability, whereas results on spatial ability were nonconclusive. Our findings provide partial support for the cognitive reserve hypothesis and demonstrate that IQ can be a significant moderator of cognitive change trajectories in old age.

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