Testosterone affects generosity

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How generously someone shares also seems to depend on testosterone levels. (Image: ronstik / iStock)

The sex hormone testosterone apparently affects how generous we are to others. In one study, subjects previously given testosterone kept more money for themselves on decision-making tasks, while subjects in the placebo group paid more attention to others. The hormone also changes brain activity: under the influence of testosterone, a connection between the parietal and temporal lobes, which is associated with consideration, is less active.

Social behavior towards fellow human beings ensures that human societies function and benefit everyone involved. How generous and helpful an individual is, however, depends on many different factors and varies considerably. Previous studies have provided evidence that sex hormones such as testosterone play a role in this. In the brain, the ability to empathize with others and to show consideration goes hand in hand with an activation of the so-called temporoparietal connection, the transition area between the parietal and temporal lobes.

Social relationship plays a role

A team led by Jianxin Ou from Shenzhen University in China has now investigated the influence of testosterone on behavior and brain activity using a combined approach. To do this, they had 67 young men solve decision-making tasks in which they could either keep a certain amount of money for themselves or share it with someone who was more or less close. Meanwhile, the researchers observed the brain activity of the test subjects in the functional MRI. Ou and colleagues had previously increased the testosterone level of some of the test subjects by putting a testosterone-containing gel on their arms and shoulders. Instead, a comparison group received a gel without an active ingredient. Neither the researchers nor the test subjects knew who had received which gel during the implementation.

“We found that testosterone leads to more selfish decisions, especially when it comes to people with whom the subject is not closely related,” the researchers report. In the case of very close people such as parents, siblings or life partners, test subjects from both groups often decided to share, with the participants being slightly less generous under increased testosterone influence. On the other hand, there was a clear difference in less close contacts, such as friends, casual acquaintances or strangers. In this case, the subjects who had received the testosterone gel were significantly less willing to forego their own profit so that the other would also get something – even if the total amount paid out would have been higher in this case.

Brain areas less active for altruism

The MRI scans told the researchers what was going on in the subjects’ brains during these decisions. In people who had received the placebo gel, there was a clear activation of the temporoparietal connection in the brain during generous decisions. “This brain region is activated when we put ourselves in other people’s shoes,” explain the researchers. “It plays a decisive role in the assumption of perspective, in moral judgments and in locating oneself in relation to others.”

In contrast, in people who received testosterone, the temporoparietal junction was less active during the decisions. The connection to other brain regions such as the insula and striatum was also weakened. These brain regions are involved, among other things, in sensory perception and the control of movement sequences. “Taken together, these results suggest that a network that encompasses areas both in the cerebrum and below the cerebral cortex underpins the effects of testosterone on social preferences,” write the Ou and colleagues.

What about women?

They note, however, that only young men between the ages of 18 and 25 took part in their study. The extent to which the results can be transferred to women, for example, cannot be determined on the basis of the data. In addition, the actual testosterone levels of the participants were not measured, so it is possible that participants who have particularly high or low levels of the sex hormone regardless of testosterone gel may have skewed the results. The personality traits of the participants were also not recorded. Further studies could provide clarity here.

Source: Jianxin Ou (Shenzhen University, China) et al., Proceedings of the National Academy of Sciences, doi: 10.1073 / pnas.2021745118

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