Longevity Briefs: Does ‘Mental Speed’ Really Slow Down After Age 20?

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: It’s generally believed that the human brain’s processing speed during decision making starts to decline after around age 20. Past research suggests that reaction times and decision making rates speed up during one’s teens until around age 20, then slow down as you get older. But is this really due to slower processing speed, or are other factors responsible?

What did the researchers do: In this study published in the journal Nature, researchers analysed response time data from 1.2 million people aged 10 to 80. This data came from another study that was originally designed to measure implicit racial bias. In that study, participants were asked to sort words or images by pressing one of two buttons. The time it took them to reach a decision was recorded.

Researchers analysed this data using a gold-standard model called a Bayesian diffusion model, in an attempt to estimate how different components of cognitive function contributed to changes in response times. This model assumed that people make decisions by processing information until they reach a certain threshold of certainty. Previously, these models had only been used on relatively small sample sizes because they are computationally demanding to run. However, researchers in this study were able to apply this type of model to their data with the aid of artificial neural networks, allowing them to process a sample size orders of magnitude larger than those previously studied.

Key takeaway(s) from this research: Just as in previous studies, the time participants took to reach decisions increased from around age 20 onwards. However, the model predicted that throughout most of midlife, this was more likely to be due to factors other than a decline in mental speed. Rather, reaction time slows because people want more certainty before making decisions as they age, because visual information takes longer to travel from the eyes to their brain, and because people take longer to physically hit the button, according to the researchers’ model.

The study therefore suggests that ‘mental speed’ may remain relatively constant between the ages of 30 and 60. The study is strengthened by its very large sample size, although we should keep in mind that all of the data comes from a particular type of simple decision-making task, and so the results might not translate well to real world scenarios.

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