NSW study finds consistency an indicator of brain health

  • Reaction times to a stimulus could indicate mortality in elderly, study says
  • Inconsistent reaction times was a predictor instead of the participant’s speed
  • Centre of Healthy Brain Ageing examined people aged 70 to 90 over eight years

The reaction times of elderly people may predict how long they have to live, according to new research. 

The new study by the University of New South Wales suggests that speed does not indicate a decline in cognitive function.

Instead, people with increasingly inconsistent reactions to stimuli had the most dramatic downturns in brain health, increasing their risk of dementia and even early death. 

People that responded slower but remained consistent showed less of a decline than those that were inconsistent.

Researchers tested reaction times in 861 elderly people through computerized tests to see if it is a neurological indicator of how long they have to live (file photo)

Researchers tested reaction times in 861 elderly people through computerized tests to see if it is a neurological indicator of how long they have to live (file photo)

Researchers at the Centre for Healthy Brain Ageing (CHeBA) at the University of New South Wales in Australia measured the variability of response on computerized reaction time tests in older people.

They then assessed each person’s risk of an early death by analyzing their medical records, conducting heart tests, brain tests, and physicals.

Comparing the two, they found that people with a higher risk of premature death from dementia or heart disease tended to display more erratic reaction times than others.

Lead author Doctor Nicole Kochan said: ‘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.

‘Our findings suggest that greater intraindividual reaction time variability is a behavioral marker that uniquely predicts shorter time to death.’  

The study examined 861 people aged 70 to 90 for eight years from CHeBA’s Sydney Memory and Ageing Study.

The participants completed two computerized reaction time tests at the start of the study and had comprehensive medical and neuropsychological assessments every two years.


The brain changes over time in size, cognition and availability of neurochemicals.

After age 40, the brain shrinks at about 5 percent per decade. These size changes are not equal in all regions of the brain. Gender is a large contributor to how the brain changes with age. 

The largest change in cognition in the brain is memory loss. Both episodic, long-term memory of events, and semantic, long-term memory of facts, decline the most with age.

Neurochemicals such as dopamine and serotonin decline over time. Dopamine starts to decline in early adulthood. It’s key responsibilities are with memory and motor function. Serotonin also declines and affects mood and social behaviors. 

Source: The Fellowship of Postgraduate Medicine 

During the timed tests the participants were presented with colored squares on a computer screen and had to touch each square as quickly as possible.

Additionally, they had to make a choice between two squares based on a pre-specified rule.

Dr Kochan said greater reaction time variability, not average speed of response time, significantly predicted survival time after researchers adjusted for known mortality risk factors, including age, sex, global cognition score and cardiovascular risk. 

As people get older, efficiency of brain processing decreases and some neurochemicals also decline. 

This can lead to an erratic type of responding which variability measures may be capturing.

She said not only as you get older, but as you get closer to death, the variability in response time becomes more exaggerated.

Co-author Professor Perminder Sachdev said the findings are an important contribution to a small but growing field investigating reaction time variability as a behavioral marker.

Professor Sachdev said: ‘Further research exploring the mechanisms involved is needed, including possible links between intraindividual reaction time variability, cognitive decline and structural and functional brain changes.’

The findings were published today in the medical journal, PLOS ONE.

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