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HomeGerontologyReaction time variation may be a marker of mortality in old age

Reaction time variation may be a marker of mortality in old age

An individual's variation in reaction times, when completing a single cognitive task across several trials, has been identified in an Australian study as an independent predictor of mortality in old age.

A common indicator of neurobiological disturbance among the elderly may also be associated with mortality, according to a study by Nicole A Kochan at the Centre for Healthy Brain Ageing (CHeBA),  University of New South Wales (UNSW) Sydney.

Intra-individual reaction time variability (IIVRT), defined as an individual's variation in reaction times when completing a single cognitive task across several trials, has been associated with mild cognitive decline, dementia and Parkinson's disease. The authors of this study investigated whether IIVRT is also associated with mortality in old age by following a cohort of 861 adults aged 70 years to 90 years over an eight-year period.

Kochan and colleagues tested the participants' baseline reaction time by having them complete two brief computerised cognitive tasks comprising 76 trials to measure the average reaction time and the extent of variation over the trials. Every two years, research psychologists followed up on the participants and conducted a comprehensive medical assessment including a battery of neuro-psychological tests to assess the participants' cognitive function. Cases were also reviewed by a panel of experts to determine a dementia diagnosis in each two-year follow-up, and mortality data was collected from the state registry.

Study results indicate that greater IIVRT predicted all-cause mortality, but the average RT did not predict time to death. Researchers found that other risks factors associated with mortality such as dementia, cardiovascular risk and age could not explain the association between IIVRT and mortality prediction. The authors suggested that IIVRT could therefore be an independent predictor of shorter time death.

"The study was the first to comprehensively account for effects of overall cognitive level and dementia on the relationship between intra-individual variability of reaction time and mortality," says Kochan. "Our findings suggest that greater intra-individual reaction time variability is a behavioural marker that uniquely predicts shorter time to death."

Intraindividual variability of reaction time (IIVRT), a proposed cognitive marker of neurobiological disturbance, increases in old age, and has been associated with dementia and mortality. The extent to which IIVRT is an independent predictor of mortality, however, is unclear. This study investigated the association of IIVRT 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 IIVRT 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 IIVRT and mean RT with survival time over 8 years during which 191 (22.2%) participants died. Greater IIVRT but not mean RT significantly predicted survival time after adjusting for age, sex, global cognition score, cardiovascular risk index and apolipoprotein ɛ4 status. After excluding incident dementia cases, the association of IIVRT with mortality changed very little. Our findings suggest that greater IIVRT uniquely predicts shorter time to death and that lower global cognition and prodromal dementia in older individuals do not explain this relationship.

Kochan NA, Bunce D, Pont S, Crawford JD, Brodaty H, Sachdev PS

[link url=""]PLOS material[/link]
[link url=""]PLOS One abstract[/link]

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