Verbal intelligence is a more robust cross-sectional measure of cognitive reserve than level of education in healthy older adults

Abstract

Background Cognitive reserve is most commonly measured using socio-behavioural proxy variables. These variables are easy to collect, have a straightforward interpretation, and are widely associated with reduced risk of dementia and cognitive decline in epidemiological studies. However, the specific proxies vary across studies and have rarely been assessed in complete models of cognitive reserve (i.e. alongside both a measure of cognitive outcome and a measure of brain structure). Complete models can test independent associations between proxies and cognitive function in addition to the moderation effect of proxies on the brain-cognition relationship. Consequently, there is insufficient empirical evidence guiding the choice of proxy measures of cognitive reserve and poor comparability across studies. Method In a cross-sectional study, we assessed the validity of 5 common proxies (education, occupational complexity, verbal intelligence, leisure activities, and exercise) and all possible combinations of these proxies in 2 separate community-dwelling older adult cohorts: The Irish Longitudinal Study on Ageing (TILDA; N = 313, mean age = 68.9 years, range = 54–88) and the Cognitive Reserve/Reference Ability Neural Network Study (CR/RANN; N = 234, mean age = 64.49 years, range = 50–80). Fifteen models were created with 3 brain structure variables (grey matter volume, hippocampal volume, and mean cortical thickness) and 5 cognitive variables (verbal fluency, processing speed, executive function, episodic memory, and global cognition). Results No moderation effects were observed. There were robust positive associations with cognitive function, independent of brain structure, for 2 individual proxies (verbal intelligence and education) and 16 composites (i.e. combinations of proxies). Verbal intelligence was statistically significant in all models. Education was significant only in models with executive function as the cognitive outcome variable. Three robust composites were observed in more than two-thirds of brain-cognition models: the composites of (1) occupational complexity and verbal intelligence, (2) education and verbal intelligence, and (3) education, occupational complexity, and verbal intelligence. However, no composite had larger average effects nor was more robust than verbal intelligence alone. Conclusion These results support the use of verbal intelligence as a proxy measure of CR in cross-sectional studies of cognitively healthy older adults.

Cognitive Reserve and Related Constructs: A Unified Framework Across Cognitive and Brain Dimensions of Aging

“…With that in mind, we showed that a measure of general cognitive ability taken during young adulthood, but not education, moderated the correlation between memory and hippocampal volume (Vuoksimaa et al, 2013 ). A similar finding has subsequently been shown for current verbal intelligence compared with education (Boyle et al, 2021 ).…”

“…Given this definition of cognitive reserve, the best available indices, i.e., operational definitions, of cognitive reserve are probably IQ or other measures of general cognitive ability because these essentially measure overall cognitive resources (Boyle et al, 2021 ). Epidemiological studies have found that higher education is associated with reduced risk for dementia (e.g., Zhang et al, 1990 ; White et al, 1994 ; Evans et al, 1997 ; Beydoun et al, 2014 ).…”

Verbal intelligence and leisure activities are associated with cognitive performance and resting-state electroencephalogram

“…Verbal intelligence was a positive predictor of perceptual organization, working memory, processing speed, and executive functions. As already reported by Boyle et al (2021) , verbal intelligence is a more robust cross-sectional measure of CR in comparison to education, occupational complexity, leisure activities, and exercise. These results are in line with the findings of the meta-analysis performed by Opdebeeck et al (2016) , where CR was positively associated with language, memory, working memory, executive function, visuospatial abilities, and general cognition.…”

Connectome-based predictive modeling of cognitive reserve using task-based functional connectivity

“…Verbal intelligence was used here as CR proxy to assess the face validity of the neuroimaging measure of CR, as it is a robust socio-behavioural proxy of CR (Boyle et al, 2021). Verbal intelligence was measured by the total number of correctly pronounced words on the American National Adult Reading Test (AMNART; Grober & Sliwinski, 1991) in CR/RANN and on an adjusted version of the National Adult Reading Test (NART; Nelson & Willinson, 1982) in TILDA (see Supplemental Information, Methods: Verbal intelligence).…”