You might associate male hormones with aggression, beards, and an affinity for performing pro-wrestling moves at home, but honesty? Probably not so much.

Testosterone plays a role in separating boys from girls, but it also influences brain development and social behavior. Some studies have found that the hormone can increase aggressive behavior, though recent studies, including one published Wednesday in the journal PLoS ONE, show that testosterone may encourage less selfish behavior in certain situations.

German researchers found that when they administered testosterone to a group of 46 men, they cheated less on a dice game than 45 men that were given placebo. In the game, the subjects rolled dice and entered their scores into a computer. A higher score meant more money at the end of the study, so there is a bit of an incentive to pad one’s score. The men weren’t monitored and couldn’t see what the other participants were entering, so there was nothing stopping them from cheating.

Measuring lying is a tricky business – ask people whether they lied may lead to underreporting of lies, while directly observing whether subjects lie will artificially skew the results towards truthfulness. Looking for lies after the fact can be biased as well, since you may be measuring not just truthfulness, but a subject’s skill in concealing a lie.

So the researchers set up their experiment to look for lying at the group level.

Statistically, all of the numbers on the die should have shown up in equal amounts, "so, if there are outliers in the higher numbers, this is a clear indication that subjects have been cheating,” senior author and University of Bonn researcher Armin Falk explained in a statement.

The researchers saw that in general, subjects that received testosterone reported lower numbers and received lower payoffs than the subjects in the control group.

"This result clearly contradicts the one-dimensional approach that testosterone results in anti-social behavior,” Falk said.

Why and how would the hormone encourage truthfulness? At this point, researchers can only guess about the neural mechanisms at play. One study suggests that testosterone affects activity in the orbitofrontal cortex, a part of the brain thought to be involved in deception.

Falk speculates that testosterone is involved in pride, and an increase in the hormone may relate to a need to develop a positive sense of self.

"Against this background, a few euros are obviously not a sufficient incentive to jeopardize one's feeling of self-worth," Falk said.

SOURCE: Wibral et al. “Testosterone Administration Reduces Lying in Men.” PLoS ONE 7: e46774, 10 October 2012.