Characterising and differentiating cognitive and motor speed in older adults: a longitudinal birth cohort study

ABSTRACT Objectives Information processing speed (IPS) has been proposed to be a key component in healthy ageing and cognitive functioning. Yet, current studies lack a consistent definition and specific influential characteristics. This study aimed at investigating IPS as a multifaceted concept by differentiating cognitive and motor IPS. Design, setting and participants A retrospective data analysis using data from the Medical Research Council National Survey of Health and Development (MRC NSHD; a population-based cohort of UK adults born in 1946) at childhood (ages 8, 11, and 15) and adulthood (ages 60-64 and 68-70). Using structural equation modelling, we constructed two models of IPS with 2124 and 1776 participants, respectively. Outcome measures Measures of interest included IPS (i.e., letter cancellation, simple and choice reaction time), intelligence (i.e., childhood intelligence and NART), verbal memory, socio-economic status (SES) and cognitive functions measured by the Addenbrooke’s Cognitive Examination III, as well as a variety of health indexes. Results We found distinct predictors for cognitive and motor IPS and how they relate to other cognitive functions in old age. In our first model, SES and anti-psychotic medication usage emerged as significant predictors for cognitive IPS, intelligence and smoking as predictors for motor IPS, while both share sex, memory, and anti-epileptic medication usage as common predictors. Notably, all differences between both IPS types ran in the same direction except for sex differences, with women performing better than men in cognitive IPS and vice versa in motor IPS. The second model showed that both IPS measures, as well as intelligence, memory, anti-psychotic and sedative medication usage explain cognitive functions later in life. Conclusion Taken together, these results shed further light on IPS as a whole by showing there are distinct types and that these measures directly relate to other cognitive functions. STRENGTH & LIMITATIONS A large longitudinal cohort data set with different measurements of information processing speed that are widely used Information processing speed is not only related to variables measured at the same time but also to childhood and premorbid intelligence and cognitive functions in later life Limitations of the cohort dataset include different response rates between waves, thus some variables were not available for all individuals at certain time points, and IPS scores were derived from a small number of trials The study involved self-reported measures which might have increased the proportion of misclassification