Why does it seem like when alcohol gets involved, people often exhibit more aggressive behavior thanks to “liquid courage”? According to a group of international researchers, it’s because changes occur in the prefrontal cortex—the area of the brain charged with tempering a person’s aggression—after two drinks.

Findings from the study were published in Cognitive, Affective, & Behavioral Neuroscience, an unofficial journal of the Psychonomic Society.

While many theories suggest alcohol-related aggression is caused by changes in the prefrontal cortex, scant neuroimaging evidence backs up these claims.

The group, led by Thomas F. Denson with the school of psychology at the University of New South Wales in Australia, used MRI to measure blood flow in the brain of 50 young men as the participants were given two drinks. They contained either vodka or a placebo that contained no alcohol.

While volunteers were lying in an MRI machine, they had to compete in the Taylor Aggression Paradigm task, which has been used for nearly 50 years in this type of research. The study team was able to see which areas of the brain were active when the task was performed and compare differences in the scans of participants who had been given alcohol and who had not.

There was no influence on the neural response of volunteers when provoked, but when behaving aggressively the prefrontal cortex of those who had received alcohol decreased.

"Although there was an overall dampening effect of alcohol on the prefrontal cortex, even at a low dose of alcohol we observed a significant positive relationship between dorsomedial and dorsolateral prefrontal cortex activity and alcohol-related aggression," said Denson in a press release. "These regions may support different behaviors, such as peace versus aggression, depending on whether a person is sober or intoxicated."

Denson and colleagues encourage increased research on a larger scale to potentially reduce alcohol-related harm in the future, according to the release.