Brain’s processing speed remains high until age of 60, study finds

Slow response time after 20 attributed mainly to increases in decision caution and slower body movement, scientists say

Previous assumptions about decline in brain speed after the age of 20 may be inaccurate, a new study found (Getty)

The human brain’s processing speed remains high until the age of 60, according to a new study that challenges previous assumptions that mental speed peaks at 20.

As humans age, it takes people longer to react to changes in our environment, or stimuli. Previous research has shown that this slowing of response time starts from the age of about 20, gradually continuing to increase as people get older.

In societies across the world, older people are often assumed to be slower thinkers than younger people, and this notion also has significant consequences in work life.

The new research, published in the journal Nature Human Behaviour on Thursday, tested this theory by analysing over a million participants across a wide age range who had taken part in an online experiment that measured their reaction times to a cognitive task.

Participants had to categorise a selection of words and images that flashed up on a screen by pushing the correct key in response.

Although the response times do seem to slow down after age 20, scientists from Heidelberg University in Germany said this could be due to increases in decision caution and to slower non-decisional processes, such as time taken to press the key.

Researchers said response times are not pure measures of mental speed but instead represent the sum of multiple processes.

They used machine learning to extract more information and find if someone responded slowly to a question, whether it was attributable to slow motor responses or slow cognitive response.

“Our results indicate that response time slowing begins as early as age 20, but this slowing was attributable to increases in decision caution and to slower non-decisional processes, rather than to differences in mental speed,” they wrote in the study.

“Only after about age 60 do drift rates start to show an accelerating negative age-related decline, with the lowest mean values found for the oldest participants,” the scientists added.

The results also suggested that people at college age (18 to early 20s) were the least cautious as they “were the most willing to trade off accuracy for speed”.

Participants aged 14 to 16, the study found, were the fastest at the mechanical part of the response, hitting the keyboard button quickly after finding the answer to the test question.

“After age 18, decision caution increases linearly until about age 65 in the incongruent condition, with a greater increase per year thereafter until age 80,” scientists noted.

Based on the research, scientists said that despite a widespread belief in age-related slowdowns in mental speed, for much of human lives, and during the timespan of a typical career, this is not likely to be the case.