Characterising and differentiating cognitive and motor speed in older adults: structural equation modelling on a UK longitudinal birth cohort

Bundil, Indra; Baltruschat, Sabina; Zhang, Jiaxiang · 2024 · Crossref

DOI: 10.1136/bmjopen-2024-083968

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Summary

This study addresses the lack of a consistent definition for information processing speed (IPS) in aging research by differentiating between cognitive and motor IPS components. While IPS is recognized as a key factor in healthy aging, previous findings have been inconsistent due to varying measurement approaches and insufficient accounting for covariances with demographic and cognitive variables. The authors aimed to clarify these relationships using structural equation modeling (SEM) on a longitudinal birth cohort, specifically investigating distinct predictors for cognitive versus motor IPS and their longitudinal association with later-life cognitive decline. The researchers utilized retrospective data from the Medical Research Council National Survey of Health and Development, a UK population-based cohort of individuals born in 1946. The analysis focused on two waves: ages 60–64 (n=2124) and ages 68–70 (n=1776). IPS was measured using three tasks: the Letter Cancellation Test (LCT) for cognitive IPS, and Simple Reaction Time (SRT) and Choice Reaction Time (CRT) for motor IPS. Additional variables included childhood intelligence, premorbid intelligence (NART), verbal memory, socioeconomic status (SES), health indexes, and medication usage. Two SEM models were constructed: Model 1 examined predictors of IPS at ages 60–64, while Model 2 assessed the predictive value of IPS, intelligence, and other factors on cognitive functions measured via the Addenbrooke’s Cognitive Examination III at ages 68–70. The results revealed distinct predictors for the two IPS types. In Model 1, SES and antipsychotic medication usage significantly predicted cognitive IPS, whereas intelligence and smoking predicted motor IPS. Sex, memory, and antiepileptic medication usage were common predictors for both. Notably, sex differences ran in opposite directions: women performed better in cognitive IPS, while men performed better in motor IPS. In Model 2, both cognitive and motor IPS, along with intelligence, memory, and specific medication usages (antipsychotic and sedative), significantly predicted cognitive functions seven years later. Sensitivity analyses using complete-case datasets largely confirmed these findings, though SES lost significance for cognitive IPS in the reduced sample. The study concludes that IPS is a multifaceted construct comprising distinct cognitive and motor components, each with unique determinants. By differentiating these components, the research clarifies that cognitive IPS is more strongly linked to socioeconomic factors, while motor IPS is associated with intelligence and smoking. Furthermore, both IPS types serve as significant indicators for later-life cognitive functioning, supporting the view that IPS acts as a buffer against age-related cognitive decline. These findings highlight the importance of treating IPS as separate constructs rather than a single unified measure to better understand its role in healthy aging.

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• cognitive capacity variation