Testosterone- the single word biological explanation accompanying the classic “Boys will be boys” slogan, oft-repeated as a rationalization for everything from mischief to bullying to violence to world wars.

The sex hormone, occurring both in men and women (albeit in a much larger quantity in men) has been commonly linked to aggression, particularly male aggression. Often described as “the essence of maleness” (which sounds like an aftershave name), age-old folklore would have you believing that this exclusive potion is responsible for strength, heroism, jar-opening skills, and “locker room talk”.

As hilarious as it is, the picture does depict a pretty popular belief- that testosterone singularly makes men more aggressive. But is that entirely true? Are violence and aggression the sole outcome? Can testosterone have “good” outcomes too? The time is now ripe for a much more nuanced discussion on the testosterone- male aggression link. Over the past decade, the onus on research has slowly shifted from focusing solely on men to include women too.

This is your brain on T.

What leads to competitive and aggressive behavior, as mediated by testosterone, in humans? Observing how the hormone influences brain response to threat provides great insight into this.

Goetz et al. (2014) studied the impact of testosterone on threat-related neural circuitry in men. After being administered either testosterone (T) or a placebo, the male participants viewed faces showing different expressions, while their brain activity was recorded by means of fMRI. As variations in baseline T- levels in participants can hamper results, the researchers successfully navigated this by administering a testosterone-agonist that ensured T-levels in all participants were at a common baseline. Results revealed that, while viewing angry facial expressions, participants on T showed greater activity in brain regions involved in threat-processing and aggression- the amygdala, hypothalamus, and peri-aqueductal gray.

Another fMRI study by Radke et al. (2015) implicated the amygdala, a region involved in fear, threat, anxiety and aggression (among several other things), in testosterone-mediated threat-processing in women. The researchers factored in motivation in the face of threat: threat approach vs threat avoidance. Female participants viewed happy and angry faces and were told to indicate rejection or approach. They found that the T-group showed greater amygdala activity only when they approached angry faces, and decreased activity during threat avoidance. They inferred that motivation plays a role in how testosterone modulates threat-processing in the brain; the increase in amygdala activity has to do with the desire to approach the threat, rather than the presence of the threat itself. The authors inferred that a) testosterone encourages threat approach by modulating amygdala activity, and b) this depends on motivation. An interesting speculation here is that, in a certain setting, testosterone can make you “braver” (or- depending on how you look at it-more foolish).

One very simple conclusion that we can draw from the above two studies: testosterone heightens threat- and aggression-related brain activity in men and women.

Preconceived notions and the benefits of T.

Is testosterone really only all about the rage and aggression? Or has the hormone been receiving an unnecessarily bad rep?

Testosterone… a good thing? You might be momentarily confused, wondering whether you accidentally clicked on to a body-building forum, but stay put for some research to back these claims up.

An illuminating study by researchers from the University of Zurich and Royal Holloway London, published as a Nature letter, explored how prejudice shapes the effect of testosterone on bargaining behaviour (Eisenegger et al., 2010). Out of the 120 women who participated, one group was administered testosterone and the other was given a placebo. To see how preconceived notions about the hormone influence behaviour, some were told that they had received a testosterone dose, even when it was a placebo, and others, who had been given testosterone, were kept uninformed. The participants then took part in the Ultimatum Game, a classic decision-making task used to study fairness/ generosity and aggression/selfishness.

The results? Women who received T without their knowledge showed increased fairness, generosity and pro-social behaviour, while the placebo group-which was told they had been administered T- exhibited more unfair, anti-social behaviour. In other words, the belief that they had received testosterone led to them behaving in a manner they believed was befitting of the controversial hormone- their prejudices about testosterone made their behavior more “aggressive”.

The link between T and altruism was further investigated in a group commonly equated to testosterone- male football fans. Reimers and Diekhof (2015) studied how endogenous T contributed to parochial altruism (i.e., ingroup favouritism and outgroup hostility). In an experimental set-up of the Prisoners’ Dilemma (this neat video might give you an idea of the conundrum), participants had to decide whether they wanted to co-operate with fans of their own favourite team (ingroup) or with fans of other teams (outgroups). It was found that, in the context of intergroup competition, high T-levels were associated with increased ingroup co-operation.

Could it be that football hooliganism is just misunderstood? Is it really all about love and brotherhood? Unlikely, but still, I’ll look forward to that study in which football hooligans are made to engage in polite, altruistic behavior in a laboratory setting.

According to the above studies, not only has testosterone been linked to increased fairness and parochial altruistic tendencies during competition, but prejudice about the hormone also seems to play a role in determining aggressive behaviour.

It might now seem as though everything you believed about testosterone and male aggression was an elaborate lie concocted by male supremacists to fuel the stereotype that women are the “weaker sex’’. Er, no, not quite. The only conclusion is this: like other hormones, the effects of testosterone can be “good” or “bad” depending on the social/environmental context, i.e. it is context-dependent.

Gender roles- not your cup of T?

Now for the Question of the Day: do social conditioning and gender roles come into play during testosterone-mediated behaviours?

In a controversial study, researchers from the University of Michigan explored how gender norms modulate testosterone levels and how “masculine” and “feminine” behaviours mediate this (van Anders et al., 2015). The study , though criticized for its methodology, highlights the need for new approaches in testosterone research.

According to societal norms, competition and wielding power are encouraged for men but discouraged for women. In a laboratory reconstruction of this typically “male” behaviour, 41 participants-actors (both male and female) performed a monologue designed to exhibit wielding power, via the role of a boss firing employees. The participants were trained to perform the monologue in two sessions- in a stereotypically masculine manner (dominance posturing, infrequent smiles, interrupting, confidence in the decision etc) and in a stereotypically feminine way (upending sentences, hesitancy, concern, trying to be nice, etc). The authors wanted to observe whether (salivary) testosterone levels change due to a) the typically “male” behavior of wielding power itself or b) the “masculine” or “feminine” performance style.

Interestingly, they found that the stereotypically male behavior of wielding power, regardless of “masculine” or “feminine” performance styles, increased testosterone levels in women. The results suggest that gender norms-that encourage aggressive behaviour in men- do seem to play some role in modulating testosterone.

In case you’re wondering- no, there isn’t any research so far linking testosterone and the stereo-typically male behaviour of “locker room talk”, but my older post on the neuroscience of political belief might help clear some of the confusion caused by recent happenings.

Getting down to the nit-T grit-T.

Before we establish a link between my unpardonable T-puns and your aggression, let’s go over a few final points.

Testosterone is neither solely responsible for aggression (as evidenced by the dual hormone hypothesis), nor is aggression the sole outcome (as evidenced by its role in empathy and altruism). Its role in aggression has been established by centuries-worth of animal research, yet human studies show inconsistent findings. The main questions generating controversy are: whether testosterone’s effects are hard-wired , and whether laboratory set-ups effectively take into account the complexity of human aggression (Eisenegger et al., 2011).

Current research is striving to combat the over-simplification of the testosterone-male aggression link, by asking skeptical questions: Are testosterone and its effects innate and fixed? Do environmental factors influence this? Clear conclusions can be reached only after looking at the topic from different angles- from the fields of developmental neuroscience, evolution, genetics, criminology, etc. While the social neuroscience findings are still plagued by inconsistencies, here is what we can take away from this post: Testosterone is a social hormone which is a) context-dependent and b) appears to be influenced by social conditioning.

The other concrete conclusion is that it’s about time the “Boys will be boys” excuse is abolished. But you didn’t need neuroscience to tell you that.

References:

Eisenegger C, Naef M, Snozzi R, Heinrichs M, Fehr E (2010). Prejudice and truth about the effect of testosterone on human bargaining behaviour. Nature; 463(7279):356–9. doi: 10.1038/nature08711.

Eisenegger C, Haushofer J, Fehr E (2011). The role of testosterone in social interaction. Trends Cogn Sci, 15(6):263–71. doi: http://dx.doi.org/10.1016/j.tics.2011.04.008

Goetz SMM, Tang L, Thomason ME, Diamond MP, Hariri AR, Carré JM (2014). Testosterone rapidly increases neural reactivity to threat in healthy men: a novel two-step pharmacological challenge paradigm . Biol Psychiatry, 76, 324–331. doi: http://dx.doi.org/10.1016/j.biopsych.2014.01.016

Radke S, Volman I, Mehta P, van Son V, Enter D, Sanfey A, et al (2015). Testosterone biases the amygdala toward social threat approach. Sci Adv, 1:e1400074. doi: 10.1126/sciadv.1400074

Reimers L & Diekhof EK (2015). Testosterone is associated with cooperation during intergroup competition by enhancing parochial altruism. Front Neurosci, 9:183. doi: http://dx.doi.org/10.3389/fnins.2015.00183

Van Anders SM, Steiger J, Goldey KL (2015). Effects of gendered behavior on testosterone in women and men. Proc Natl Acad Sci U S A, 13805–13810. doi: 10.1073/pnas.1509591112