Study reveals a crucial way hormones in puberty alter men's brains

Adolescence can be an emotional whirlwind, fueled by hormones run riot. The turbulent years between the ages of 12 and 18, collectively known as puberty (or should it be purgatory...), are a rollercoaster of new and extreme feelings and experiences — a time some prefer to forget, but which ultimately forms us into the adults we become.

This period of neurodevelopment is critical, yet relatively little is known about how this turbulent time shapes brain function in adulthood. But a growing body of research suggests hormones in puberty may fundamentally alter our perception in adulthood — including our powers of social perception.

What's new — A study published Monday in the Journal of Neuroscience reveals a connection between testosterone levels in puberty to the ability to perceive faces in adult men. Specifically, the study involves men aged around 19, and considers how their brains respond to other people's faces — a key point of social interaction.

Testosterone is a critical hormone in male development. In men, it is involved in growth and development, sperm production, and sex drive. It also affects the brain — and because interpretation of facial cues is so central to navigating our complex social environment, this new information could help us better understand how — and why — young men interact with the world around them in certain ways.

How they did it — This study relies on data collected in an ongoing, longitudinal study called the Avon Longitudinal Study of Parents and Children. This study recruited pregnant women in Avon, England, who gave birth in the early '90s and follows them and their children.

The researchers used data from 507 young men from the study collected over the ages of 9 to 17, and then again at age 19 or 20.

First, the researchers measured the testosterone levels in the men's blood during adolescence, here defined as between the ages of 9 and 17. Then, at about age 19, the young men gave saliva samples to researchers, who measured their testosterone levels once more.

On the same day, the young men underwent an fMRI brain scan while watching videos of faces to see how their brain activity may be affected by their testosterone levels both during adolescence and on the day of the scan.

What they discovered — In the 25 regions of the men’s brains the researchers analyzed, those with low exposure to testosterone during their adolescence were more sensitive to present testosterone levels.

In other words, their brain’s response to faces was strongly linked to their current testosterone — but the same wasn’t true for men who had medium or high testosterone levels during adolescence. Rather, it was the degree of difference in testosterone level which seemed to be influencing the men's brain activity.

“It seems that if, for whatever reason, during puberty you had relatively low testosterone levels, then when you were a young man and for whatever reason, on that day [of the study] you happened to have a relatively high level of testosterone, then you respond more strongly to faces,” Tomas Paus tells Inverse. Paus is a professor at the University of Toronto, Canada, and the study's senior author.

Whether or not the participants had high or low testosterone when they came in for the brain scans could have to do with mood, Paus says. Testosterone levels could have been unusually high, for example, if one of the men had just won a game, for example, but low if they had just failed an exam.

Digging into the details — Interestingly, Paus and his team link testosterone levels to how well the brain processes social cues specifically stemming from eye movements. Humans make sense of facial expressions and infer non-verbal communication largely from watching other people's eyes. In this study, the researchers find those men who had low levels of testosterone in adolescence may be more attuned to facial cues in later life. This was particularly true of facial cues signaling a potential threat.

According to Paus, this study is one of the first to link the effect of testosterone in puberty to brain responses to faces in adulthood. He notes the results strengthen the hypothesis that, though hormones do drive our behavior as adults, how much power they exert may depend on our long-gone adolescent chemistry.

Why it matters — High testosterone is often associated with aggression or anger, but this study shows it’s more complicated than that. Testosterone is associated with power-seeking in many social contexts. David Terburg is an assistant professor at the Utrecht University in the Netherlands whose research centers on automatic social and emotional processes. He explains to Inverse why testosterone's influence on the brain can't be reduced to such stereotypes.

“In a safe situation, testosterone, while still facilitating status and dominance, can help you to be more prosocial,” Terburg says. He was not involved in the new study. “So testosterone is not a bad, aggressive hormone of aggression. It has different sides.”

When it comes to faces, testosterone plays a multifaceted role. Facial mimicry, for example, poses a potential disadvantage in a competition for status, and testosterone may reduce facial mimicry.

In turn, an increase in testosterone can make women more likely to hold a “dominant gaze” — that is, to stare someone down in a primordial bid to gain status and power over them. In a different study, women who received a dose of testosterone had more trouble identifying emotions from faces, but those with social anxiety who were given testosterone averted their eyes less in social situations.

“You can stare someone down, so that's the dominance aspect,” Paus says. “But you can also be more attuned with someone.”

Taken together, the results suggest young men with lower adolescent testosterone may be better at looking for signs of a threat in the eyes of another — and perhaps even better assert dominance on a testosterone high later in life. They may also be better at interpreting social cues because they’re paying more attention to people's facial expressions, the researchers suggest.

What's next — This study does not answer why some men have less adolescent testosterone than others. Paus says this is one of the questions he and his colleagues want to try and answer next. It’s also unclear what exactly the stronger response to faces could mean for men in real-life social situations.

For now, the answer may be “it depends,” Paus says.

“I would say that those boys [with lower adolescent testosterone] are in somewhat advantageous positions. By concentrating more on the eyes, they are in a better position to detect particular signals,” Paus says.

Abstract: According to the organizational-activational hypothesis, organizational effects of testosterone 42 during (prenatal) brain development moderate activational effects of adult testosterone on 43 behavior. Accumulating evidence supports the notion that adolescence is another period during 44 which sex hormones organize the nervous system. Here we investigate how pubertal sex45 hormones moderate the activational effects of adult sex-hormones on social cognition in humans. 46 To do so, we recruited a sample of young men (n=507, ~ 19 years of age) from a longitudinal 47 birth cohort, and investigated if testosterone exposure during adolescence (from 9 to 17 years of 48 age) moderates the relation between current testosterone and brain response to faces in young 49 adulthood, as assessed with functional magnetic resonance imaging (fMRI). Our results showed 50 that the cumulative exposure to testosterone during adolescence moderated the relation between 51 adult testosterone and both the mean fMRI response and functional connectivity (i.e., node 52 strength). Specifically, in participants with low exposure to testosterone during puberty, we 53 observed a positive relationship between current testosterone and the brain response to faces; this 54 was not the case for participants with medium and high pubertal testosterone. Furthermore, we 55 observed a stronger relationship between the brain response and current testosterone in parts of 56 the angry-face network associated with (vs. without) motion in the eyes region of an observed 57 (angry) face. We speculate that pubertal testosterone modulates the relationship between current 58 testosterone and brain response to social cues carried by the eyes, and signaling a potential threat