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Inconsistent Reaction Time Predicts Mortality

Inconsistent performance in responding to a stimulus, rather than the speed with which one responds, is a marker of accelerated ageing and predicts mortality in older people, according to research published in PLoS ONE.

Scientists at the UNSW Centre for Healthy Brain Ageing measured the intraindividual variability of reaction times in older adults, and found that it predicted survival time after accounting for any signs of decline in cognitive functioning that may herald dementia.

Lead author Dr Nicole Kochan said the study was the first to comprehensively account for the effects of overall cognitive level and dementia on the relationship between mortality and variability of intraindividual reaction time. “Our findings suggest that greater intraindividual reaction time variability is a behavioural marker that uniquely predicts shorter time to death,” she said.

“Importantly, the predictive strength of intraindividual reaction time variability was virtually unchanged when we removed participants who developed dementia over the subsequent 8 years. This suggests that variability of reaction time is an independent risk factor and not simply a corollary of general cognitive decline or neuropathological disturbances associated with dementia.”

The study examined 861 community-dwelling participants aged 70–90 years over 8 years. Participants completed two computerised reaction time tests at baseline and as part of comprehensive medical and neuropsychological assessments every 2 years.

Participants were presented with coloured squares as stimuli on a computer screen, and were required to touch each square as quickly as possible. On a more complex level each participant was required to choose which of two squares they touched depending on a pre-specified rule.

Greater intraindividual reaction time variability, but not average speed of response time, significantly predicted survival time after adjusting for known mortality risk factors, including age, sex, global cognition score, cardiovascular risk and apolipoprotein-e4 status.

“The findings add to our previous research showing that measures of reaction time variability are sensitive to other age-related neuropathological states, including preclinical dementia and falls,” Kochan said.

Kochan explained that erratic responses may tap into the efficiency of brain processing. “As you get older, efficiency of brain processing decreases and some neurochemicals also decline, leading to the erratic type of responding which variability measures may be capturing,” she said. “Potentially not only as you get older, but as you get closer to death, the variability in response time becomes more exaggerated.”