Your brain doesn’t slow down until your 60s – later than we thought

Although people take longer to make decisions from age 20 onwards, this may not be due to a decline in the speed of information processing, a large study has found

By Carissa Wong

Our ability to process information during decision-making doesn’t drop off until age 60, according to new findings that challenge the widespread belief that mental speed starts to decline in our 20s.

Mischa von Krause at Heidelberg University in Germany and his colleagues analysed data collected from around 1.2 million people aged 10 to 80 who took part in an experiment that was originally designed to measure implicit racial bias.

During the task, participants were asked to sort words and images, for example by labelling faces as white or Black, or classifying words such as “joy” or “agony” as good or bad, by pressing one of two buttons.

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In support of previous studies, the researchers found that people’s reaction times speed up from their teens to around age 20, then slow down as they get older. This decline has typically been attributed to slower mental speed, but this isn’t the case, says von Krause.

The team used an established model of cognition based on previous research, which assumes people make decisions by continuously considering information until they reach a threshold of certainty.

According to this model, the decrease in reaction time from age 20 is probably due to people wanting more certainty before making decisions as they age, visual information taking more time to travel from their eyes to their brain and people taking longer to physically hit the button as they get older.

The analysis suggests that people’s mental speed increases in their 20s, and stays high until age 60. “Until older adulthood, the speed of information processing in the task we studied barely changes,” says von Krause.

“People become more cautious in their decisions with increasing age – they try to avoid mistakes. At the same time, the motor processes – the pressing of the response keys in an experiment – slow down with increasing age.”

The findings challenge the assumption that people in their 40s and 50s are mentally slower than young adults. This can affect real-life outcomes, such as who gets hired or promoted in the workplace, says von Krause.

While the team expects the results will apply to a wide range of cognitive tasks, it is possible that age may affect other tasks differently, such as those relying on memory.

The study supports smaller studies that have also found a decline in mental speed from around age 60.

“The work replicates what has been done before, but with much larger numbers of people and so provides strong converging evidence for the earlier results,” says Roger Ratcliff at Ohio State University.

Journal reference: Nature Human Behaviour, DOI: 10.1038/s41562-021-01282-7