Whenever there’s a quarrel, fist-fight or bar brawl, testosterone usually has something to do with it. Famous for fuelling aggression, this male sex hormone is the prime suspect behind the human tendency towards antagonism, and with good reason. According to a new study in the journal Psychoneuroendicinology, testosterone reduces connectivity in brain regions responsible for feeling empathy towards others and incorporating this sentiment into our decision-making.

Led by scientists from Utrecht University, the researchers sought to build on previous studies in which women were found to outperform men on tasks designed to measure empathetic capabilities. During these studies, participants were subjected to the Reading the Mind in Eyes Tests (RMET), in which the emotions and motives of others must be determined simply by looking at a picture of their eyes.

Suspecting that testosterone may have been responsible for the inferior performance of males when conducting this test, the researchers set up a new experiment to measure how the hormone influences success rates, while tracking its effects on the brain.

Recruiting a group of 16 female volunteers, the study authors used functional magnetic resonance imaging (fMRI) to measure their brain activity as they performed the RMET. In doing so, they discovered that a brain region called the inferior frontal gyrus (IFG) became specifically activated whenever they were required to associate an emotion with an image, suggesting that it plays a primary role in empathizing with others.

Following this, half of the participants were orally administered a large dose of testosterone in order to temporarily elevate their blood levels of the hormone by a factor of ten, while the other half received a placebo.

Upon repeating the RMET, those who had received testosterone took significantly longer to identify the emotions being expressed in the pictures than those who had received the placebo, indicating that the hormone did indeed impair their capacity for empathy.

^{The ability to incorporate an awareness of the feelings of others into our decision-making processes may be disrupted by testosterone. Bacho/Shutterstock}

FMRI scans during this second round of testing showed that connectivity between the IFG and two other key areas – the anterior cingulate cortex (ACC) and the supplementary motor area (SMA) – were significantly reduced following the administration of testosterone. Importantly, the ACC is known to play a role in incorporating emotionally affective states into overall cognitive control processes, while the SMA is involved in initiating voluntary action.

Based on these findings, the study authors suggest that by interrupting the IFG-ACC-SMA network, testosterone impairs one’s ability to integrate the feelings and motives of others into one’s own cognition, decision-making, and actions. However, since they did not measure the behavioral outcomes of this effect, they can only hypothesize at this stage as to the actual impact that this reduced empathetic capability has on a person’s conduct.

Concluding, the researchers propose that developing new ways to regulate the effects of testosterone may provide effective treatments for certain autism-related symptoms, by rebalancing a neural network that they say “is critical for the integration of sensory information, selection, and action preparation.”