Is intraindividual reaction time variability an independent cognitive predictor of mortality in old age? Findings from the Sydney Memory and Ageing Study

Abstract

Intraindividual variability of reaction time (IIV RT ), a proposed cognitive marker of neurobiological disturbance, increases in old age, and has been associated with dementia and mortality. The extent to which IIV RT is an independent predictor of mortality, however, is unclear. This study investigated the association of IIV RT and all-cause mortality while accounting for cognitive level, incident dementia and biomedical risk factors in 861 participants aged 70-90 from the Sydney Memory and Ageing Study. Participants completed two computerised reaction time (RT) tasks (76 trials in total) at baseline, and comprehensive medical and neuropsychological assessments every 2 years. Composite RT measures were derived from the two tasks-the mean RT and the IIV RT measure computed from the intraindividual standard deviation of the RTs (with age and time-on-task effects partialled out). Consensus dementia diagnoses were made by an expert panel of clinicians using clinical criteria, and mortality data were obtained from a state registry. Cox proportional hazards models estimated the association of IIV RT and mean RT with survival time over 8 years during which 191 (22.2%) participants died. Greater IIV RT but not mean RT significantly predicted survival time after adjusting for age, sex, global cognition score, cardiovascular risk index and apolipoprotein ε4 status. After excluding incident dementia cases, the association of IIV RT with mortality changed very little. Our findings suggest that greater IIV RT uniquely predicts shorter time to death and that lower global cognition and prodromal dementia in older individuals do not explain this relationship.

Water-Based Exercise and Resistance Training Improve Cognition in Older Adults

“…These results can be interpreted in view of the evidence suggesting that the neurodegenerative process of aging has an initial impact in the white matter, affecting cortical pathways in a fronto occipital gradient, leading to impairments in executive function and processing speed. 13,24,25 Our findings are in agreement with previous studies that point out reaction time assessments as sensitive early marker of subtles changes in cognition of community-dwelling health older adults and pathological aging, [6][7][8] indicator of quality of life, 26 as well a predictor of functional decline 27 and shorter time to death 28 and is associated with functional mobility. 29 The neuroprotection of alpha motor neurons and motor endplate found in senile exercised rats 30 may also support the shorter movement latency founded in exercised groups.…”

Cognitive Function and Mortality: Results from Kaunas HAPIEE Study 2006–2017

“…Cognitive abilities are associated with health literacy, as people with lower cognitive function may be less able to engage in a healthy lifestyle and are less able to follow specialist instructions [19,29]. Additionally, people with lower cognition are unable to engage in a healthy lifestyle [22,30]. Moreover, cognitive functions might affect health as a part of a multi-dimensional concept like frailty, where it works along with other factors such as exhaustion, weight loss, etc.…”

“…Another study found that cognitive decline, on the contrary, decreases the risk of cancer mortality [20]. Moreover, previous studies found that specific cognitive functions such as short-memory or cognitive speed may be differently associated with mortality than the total cognitive score [21,22]. This study explored associations between different cognitive functions and different causes of death accounting for significant covariates in the representative sample.…”

Subcortical Ischemic Vascular Cognitive Impairment: Insights from Reaction Time Measures

“…IIV is a behavioral representation of the transient fluctuation of RT over a given number of trials related to various aspects of information processing. These include (but are not limited to) attentional control and lapses, stimulus-and post-perceptual-processes and strategies, the functional and structural integrity of white and grey matter, and the status of distributed neural, and neurobiological networks [26,27,[42][43][44][45][46][47][48][49][50][51][52][53][54]. Although RT and IIV can correlate (i.e., slower RT associated with greater IIV), thus appearing to share common networks, the relationship between them is not always linear.…”