By Emma Young

The hot-headed “macho man”, who acts first and thinks later, has long been popular in movies. Now there’s psychological evidence to support it. A new study in the Psychological Science finds that a short-term rise in testosterone – as might occur when in the presence of an attractive potential mate, or during competition – shifts the way men think, encouraging them to rely on quick, intuitive, and generally less accurate, judgements, rather than engaging in careful, more deliberate thought.

In the biggest investigation of the effects of testosterone on human behaviour to date, a team from Caltech, the University of Pennsylvania, Western University and the ZRT Laboratory in Oregon, recruited 243 men, mostly college students. The men rubbed a gel that they were told either contained testosterone or was a placebo over their shoulders, upper arms and chest. Four-and-a-half hours later – enough time for their testosterone levels to peak – they embarked on a series of tests (saliva samples taken from the men through the study confirmed that testosterone levels were indeed higher in the group that applied the gel that contained testosterone).

The most critical test, in terms of the study aims, was the three-item Cognitive Reflection Test, which evaluates a person’s ability to override quick and intuitive, but likely incorrect, judgements through deliberate, careful thought. The volunteers were told that they’d be paid $1 for each correct answer, with a bonus of $2 for three correct answers, and they could take as long as they liked.

An example from the test: A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?

Earlier work has found that, when presented with this question, most people go with their first thought, and answer, incorrectly, 10 cents – even though it is straightforward to check the answer, which would show that 10 cents is wrong. With a little deliberation, it’s not too difficult for most people to work out the right answer*.

The researchers found that the men who’d received testosterone performed significantly worse on this test. Overall, they came up with 20 per cent fewer correct answers than the men who’d received the placebo. What’s more, when volunteers who’d received testosterone gave correct answers, they tended to do this more slowly than the volunteers who’d got the placebo. While the team didn’t measure individual volunteers’ testosterone levels, based on previous work on the dose used (100 mg of topical 1 per cent testosterone), they were probably at around the level that young men experience during real-world competition, the researchers say.

The tasks also included an arithmetic test, and those who’d got the testosterone did as well as the others. The researchers take this to show that it was the men’s ability to reflect on their first impulses that was affected by the testosterone dose, rather than their level of engagement in the study, their motivation or their arithmetic skills.

“Our results demonstrate a clear and robust causal effect of testosterone on human cognition and decision making,” the researchers write. “The influence of testosterone on the Cognitive Reflection Test, alongside its lack of effect on the arithmetic control task, suggests that testosterone decreases … the probability of engaging in slow and effortful cognitive processes but keeps the capacity to perform them intact.”

The context will determine whether this is bad news or not. Rapid intuitive responses could be beneficial for increasing the chance of having sex or succeeding at a physical challenge, the researchers observe. But they could be detrimental in the workplace – or an exam room. Is this an argument, then, for gender separation in classrooms?

The volunteers were all male, so the study tells us nothing about the effects of testosterone on thinking in women (who also produce the hormone, but at lower levels). And the study doesn’t identify what might mediate the greater reliance on intuitive decision-making with raised testosterone – over-confidence, perhaps?

Male testosterone levels gradually fall with age, and some older men use testosterone ‘replacement’ gels, often at the dose used in this study, or inject the hormone. “Western society has been experiencing an exogenous testosterone ‘shock’ over the past decade from a rapidly growing testosterone-replacement-therapy industry,” the researchers write, in a final note. “The possibility that this widely prescribed treatment has unknown deleterious influences on specific aspects of decision making should be investigated further and taken into account by users, physicians and policymakers.”

More work is now needed to explore the effects of testosterone supplements in older men (whose levels are lower to start with), as well as to better understand how testosterone levels fluctuate naturally in day to day life – and so the likely effects on cognition.

—Single-Dose Testosterone Administration Impairs Cognitive Reflection in Men

*The bat costs $1.05 and the ball costs 5 cents.

Emma Young (@EmmaELYoung) is Staff Writer at BPS Research Digest