Testosterone can reduce a man’s “social brain” function and dampen his generosity, according to a new study.
The higher the testosterone level, the less neural activity occurred in the temporoparietal junction, an area in the upper human brain associated with social functions, said the researchers in a paper published in the peer-reviewed PNAS, the Proceedings of the National Academy of Sciences of the United States of America.
Wu Yin, a lead author of the study with Shenzhen University’s school of psychology, said their discovery might help explain why some men were more selfish than others.
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“There is mounting evidence suggesting that people with higher testosterone levels behave more aggressively or selfishly,” he said.
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Wu and his colleagues recruited nearly 70 healthy Chinese young men for their experiment to find out if testosterone affected generosity – and how.
The participants were divided in two groups, one taking a testosterone pill and the other a placebo. The researchers then asked each participant whether he was willing to take some money (equivalent to US$20-45), or split the money with another person. That person could be a close family member, relative, friend, colleague or a complete stranger.
The men taking the pills were less willing to share the money with others, including strangers.
The researchers monitored the brain activity of the participants when they made the choice, and found the temporoparietal junction, or “social brain”, had less activity than the placebo group.
To the researchers’ surprise, the junction’s communication with other parts of the brain also decreased, suggesting that the impact of the hormone could be broader than previously thought.
Liu Xun, deputy director of the Institute of Psychology at the Chinese Academy of Sciences in Beijing, said sex hormones were known to affect thinking and behaviour.
Men with excessive testosterone were, for instance, more likely to engage in violence, Liu said. Oxytocin, a hormone generated by mothers during childbirth, stimulated altruism, a tendency to help others, he said.
Brain involvement in these phenomena remain poorly understood. The new findings would help solve the puzzle, said Liu, who was not involved in the study.
“But the role of sex hormone must not be extrapolated too far,” he said.
Liu said traits such as selfishness were extremely complex mental activities, and they could be affected by a wide range of factors. Some were present from birth, some were environmental, some stayed for life, some changed over time.
A man’s testosterone level typically declines with age, and older men often appear to be less self-centered than pubescent males, when the testosterone levels peaked, he said.
But the older man’s more consideration for others could also be a result of his increasing life experience, Liu said.
“Hormones may play an important role in a controlled laboratory experiment, but in real life many other things can be at play, sometimes we may not be able to separate one from the other,” Liu said.
On the limits of their study, Wu and colleagues said the detailed molecular changes caused by testosterone to a man’s brain remained largely unknown, and how hormones affected the generosity of women also required further study.
This article How can testosterone make men selfish? A Chinese study offers clues first appeared on South China Morning Post