A new study reveals why there’s such a strong association between increased testosterone levels and anti-social behavior. While testosterone is produced in the testicles or from the adrenal glands, its effect on behavior links back to the brain. These newly identified neural mechanisms can, in turn, influence how an individual acts.
This finding was published Monday in the journal Proceedings of the National Academy of Sciences.
What they did — A team of researchers from China and Switzerland split 70 healthy males between the ages of 18 and 25 into two groups. Researchers rubbed 150 milligrams of a testosterone gel on the shoulders and upper arms one the testosterone group, and a placebo gel on the shoulders of the placebo group.
The participants were then introduced to the concept of social distance — not the kind we’ve all been doing for the past year, but social distance as it relates to emotional closeness to another person. For example, if your grandmother is your favorite person in the world, you have a high degree of social closeness with her. If there’s a guy you see while you’re each walking your dogs every morning, but never interact with, you have a significant degree of social distance from him.
Researchers explained this concept to the subjects and then asked them to rate their closeness to various individuals on a 20 point scale — 20 being maximum closeness. The categorization of these individuals included, but wasn’t limited to, parents, colleagues, and strangers.
If the subject had a negative relationship with any of the suggested individuals, they were removed from the survey. The researchers were only interested in people the subjects either felt neutrally or positively towards.
Then, the study team brought in some cash. The subjects were asked to pick people whose distance they rated within the range of 1, 2, 3, 5, 10, and 20, 50, and 100. For all but the acquaintances and strangers (people categorized as 50 and 100 respectively), the subjects provided their contact and payment information. Subjects in each group were then offered between 130 and 290 CNY (Chinese Yuan); the equivalent of about $20 to $44.60 U.S. dollars.
The participants were then presented with their selected individuals in varying degrees of social closeness. The researchers, in turn, randomly selected one of the participant’s chosen people and asked to them make a decision: they could either choose to keep all of the money, the most selfish option, or split the money evenly with the other person, the most generous option. If they chose to split the money with the people they rated 50 or 100, the money would go to someone a random person in the same building or on the same campus, respectively.
The researchers ran the subjects through this decision-making process with different combinations of selfish amounts (how much money they would get if they kept it all), and different social distances between the subject and the other person who would receive the money. The subjects’ brain activity was also monitored via fMRI.
Digging into the details — In particular, the researchers were looking at the two areas of the brain:
1) The temporoparietal junction (TPJ): This is the area of the brain associated with social cognition and the ability to have empathy and understand others’ perspectives.
2) The area of the brain extending from the insula to the striatum associated with reward and the ability to evaluate how much you want something.
In short, they were looking at the parts of the brain associated with generosity.
What they discovered — First, their findings confirmed other research associating selfishness and testosterone. Both groups were roughly the same in their generosity towards people they were socially close to, but as social distance increased, subjects who received the testosterone gel were much less likely to split the money.
Co-author Yin Wu, a researcher from Shenzhen University’s Shenzhen School of Psychology, tells Inverse the study suggests testosterone decreases activity in the brain’s temporoparietal junction (TPJ), which is a region associated with generosity.
This finding is “compatible with the notion that testosterone reduces consideration of the needs and desires of others, which leads to more selfish behaviors,” the team writes.
In the placebo group, the connection between the right TPJ and the area extending from the insula to the striatum was stronger than it was in the testosterone group. This suggests these areas of the brain “talking” to each other drives more generosity — and that testosterone may suppress that activity.
The big takeaway — The researchers are careful to note that their findings don’t necessarily suggest testosterone inherently makes people selfish, but that testosterone “reduced concern for the profits of others.”
While this study only looked at healthy, young adult males — and thus may or may not apply to other ages and genders — it does add to the pile of studies suggesting increased testosterone can lead to decreased consideration for the needs of others. What this study also reveals are the neural mechanisms by which that happens.
No matter what your gender is, sex hormones have a distinct and often powerful effect on our behavior. Perhaps better understanding what’s happening in our brain when those hormones are heightened can help us correct that behavior towards better outcomes. Other researchers argue classic “testosterone-fueled behavior” is more a result of nurture than nature — future research may reveal it’s a balance of both.
Abstract: Recent evidence has linked testosterone, a major sex hormone, to selfishness in economic decision-making. Here, we aimed to investigate the neural mechanisms through which testosterone reduces generosity by combining functional MRI with pharmacological manipulation among healthy young males in a double-blind, placebo controlled, between-subject design. After testosterone or placebo gel administration, participants performed a social discounting task in which they chose between selfish options (benefiting only the participant) and generous options (providing also some benefit to another person at a particular social distance). At the behavioral level, testosterone reduced generosity compared to the placebo. At the neural level (n = 60), the temporoparietal junction (TPJ) encoded the other-regarding value of the generous option during generous choices, and this effect was attenuated by testosterone, suggesting that testosterone reduced the consideration of other’s welfare as underpinned by TPJ activity. Moreover, TPJ activity more strongly reflected individual differences in generosity in the placebo than the testosterone group. Furthermore, testosterone weakened the relation between the other-regarding value of generous decisions and connectivity between the TPJ and a region extending from the insula into the striatum. Together, these findings suggest that a network encompassing both cortical and subcortical components underpins the effects of testosterone on social preferences.