Reaction time variation may be a marker that predicts mortality in old age

Intraindividual 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 computerized 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 neuropsychological 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 intraindividual variability of reaction time and mortality," says Kochan. "Our findings suggest that greater intraindividual reaction time variability is a behavioural marker that uniquely predicts shorter time to death."