A Systematic Review of Longitudinal Associations Between Reaction Time Intraindividual Variability and Age-Related Cognitive Decline or Impairment, Dementia, and Mortality

Abstract

Objective: Intraindividual variability (IIV) in reaction time refers to the trial-to-trial fluctuations in responding across a given cognitive task. Cross-sectional research suggests that IIV increases with normal and neuropathological ageing and it may serve as a marker of neurobiological integrity. This raises the possibility that IIV may also predict future cognitive decline and, indeed, neuropathology. Therefore, we conducted a systematic review to address these issues. It is well established that adult ageing is characterised behaviourally by increased intraindividual variability in cognitive function. As the present review will show, such variability is not only a feature of normal ageing, but becomes more marked in the presence of neuropathology or impending mortality. It is likely that this widely observed behavioural characteristic of ageing reflects greater neurobiological variability stemming from compromised central nervous system integrity. Given the proposed neurobiological underpinnings of IIV, the aim of the present systematic review, therefore, was to critically evaluate the empirical literature using this marker to predict cognitive change in normal ageing, and also age-related neuropathological outcomes including mild cognitive impairment (MCI), dementia, Parkinson's disease and, indeed, death. First though, we describe some of the characteristics of this behavioural marker before detailing theoretical and empirical linkage to potential underlying neurobiological variability.

Reaction times match IQ for major causes of mortality: Evidence from a population based prospective cohort study

“…A contrary view posits that variability in reaction times, whether trial to trial variability within a task (as in RT SD) or task to task variability (such as test-retest reliability), do not only reflect measurement error but are indicators of systematic underlying, usually pathological, processes ( Bunce, MacDonald, & Hultsch, 2004 ). The proponents of this theory point to increased RT variability associated with a number of neurological conditions ( Hetherington, Stuss, & Finlayson, 1996 ) and to studies where RT SD is more predictive than mean RT ( Haynes, Bauermeister, & Bunce, 2017 ). The results here are not consistent enough across causes to provide evidence either for or against this hypothesis.…”

Neural circuitry underlying sustained attention in healthy adolescents and in ADHD symptomatology

“…IRV is particularly advantageous in that it is a relatively simple measurement that controls for overall speed of responding (e.g., it can be calculated as the standard deviation of RT divided by mean RT). IRV may provide a better metric of cognitive impairment than other neuropsychological test measures, such as standardized cognitive or psychomotor tasks (Haynes et al, 2017;Balota et al, 2010;Cherbuin et al, 2010) or simple RT (Dixon et al, 2007). Attentional deficits are commonly reported in attention deficit hyperactivity disorder (ADHD) during both laboratory tasks and in daily life (Klein et al, 2006;Leth-Steensen et al, 2000;Russell et al, 2006;Tamm et al, 2012;Barkley, 1997;Sonuga-Barke and Castellanos, 2007), with higher IRV commonly reported in ADHD (Kuntsi and Klein, 2011;Castellanos et al, 2006;Mullins et al, 2005;Kofler et al, 2013;Vaurio et al, 2009;Castellanos et al, 2005;Bellgrove et al, 2005).…”

Response Time Consistency Is an Indicator of Executive Control Rather than Global Cognitive Ability

“…More recently, it has been shown that RT IIV was predictive of declining fluid abilities including memory, speed, reasoning, and fluency, whereas no change was observed in verbal performance (reflecting crystalized ability) (Bielak et al, 2010). A recent systematic review verified cognitive associations with RT IIV, and that inconsistency precedes cognitive decline in aging (Haynes, Bauermeister, & Bunce, 2017). Of note, previous studies have not consistently included common neuropsychological tests from clinical practice, nor have they examined the RT parameters that contributed to these associations.…”