High levels of testosterone may reduce empathy by interfering with communication between parts of the brain involved in emotion, according to a study to be published in the journal Psychoneuroendicinology.

There is a large body of scientific research linking testosterone, a hormone produced in larger quantities by men’s bodies and in smaller quantities in women’s bodies, with impairment in the ability to cognitively process emotional information. This applies particularly processes related to empathy, the ability to correctly identify another person’s emotional state based on cues like facial expression and body language. Women perform consistently better at tasks requiring empathy than men.

People with signs of having been exposed to higher levels of fetal testosterone in utero also score lower on measures of empathy, regardless of gender. Others research has found that women who are given injections of testosterone under laboratory conditions experience temporarily reduced empathy. It has been theorized that these effects are due to the direct impact of testosterone on the function of areas of the brain related to emotion.

A new study led by Peter Bos, of Utrecht University, sought to discover the neural effects of testosterone in relation to cognitive processing involved in empathy. Sixteen female college students volunteered to have their brains monitored using functional magnetic resonance imaging (fMRI) while they completed a task that measured their ability to be empathetic. The task required them to look at images of the area of the face immediately around the eyes and identify, within three seconds, whether the expression matched a given emotional state (such as hostile or playful).

Half of the women were given an orally administered dose of testosterone sufficient to increase the levels of the hormone in their blood by a factor of ten, while the other half received a placebo. The women who were given testosterone subsequently took significantly longer to identify the emotions depicted images of eyes, and made significantly more errors while doing so.

At the same time, fMRI images showed that there was significantly less activity in the pathways connecting the inferior frontal gyrus (IFG), a part of the frontal cortex involved in processing emotional cues from others, with the supplemental motor area (SMA) and the anterior cingulate cortex (ACC), two closely-connected areas thought to be involved in regulating and acting on one’s own emotions.

The study’s authors conclude that high levels of testosterone have a negative impact on empathy because of the hormone’s effects on the emotional processing network formed by the IFG, SMA, and ACC. By reducing connectivity between these regions, testosterone may make it harder to interpret emotional cues from others and effectively connect those interpretations with appropriate emotional responses.

The authors suggest that this process may play a role in autism spectrum disorders, which affect emotional processing and have been potentially linked with high levels of fetal testosterone exposure. They also shed some light on how some of the stereotypical differences between women and men may be based in neurochemistry.