Drinking and fighting are an age-old pair — but why? Using functional magnetic resonance imaging (fMRI), Australian researchers found that as little as two drinks can impair the part of the brain that tempers our aggression levels.

Drunk octopi.

Image credits Adrian Scottow / Flickr.

We don’t actually know why people become more aggressive after imbibing. We have our hypotheses, sure — mainly that alcohol-related fisticuffs are borne of an impaired prefrontal cortex — but there wasn’t much neuroimaging evidence to back that hypothesis up.

Gray matter matters

That’s a chink in the data that a team from the University of New South Wales in Australia patches up in their new paper. Led by Thomas Denson, the team recruited fifty healthy young men and gave each two drinks — either vodka or a placebo. After the volunteers downed their drink, the team placed them in a fMRI machine and pitted them against a standard test aimed at observing levels of aggression in response to provocation.

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Functional magnetic resonance imaging allows researchers to see changes in blood flow throughout the brain — which they can then use to infer brain activity. They used these readings to see what parts of the areas this task activated. They also used the brains of participants in the control group as a baseline and compared the readings of those in the alcohol group to this baseline.

They report that being provoked had no influence on the participants’ neural responses. However, when behaving aggressively, those who had consumed alcoholic drinks had a dip in their prefrontal cortex activity. This dampening was also seen in areas f the brain involved in the reward pathways, and the hippocampus — a part of the brain associated with memory — saw heightened activity.

“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,” Denson explains.

“These regions may support different behaviors, such as peace versus aggression, depending on whether a person is sober or intoxicated.”

The results are consistent with other current research on the neural basis of aggression, and its relationship to the prefrontal cortex, the limbic system, and reward pathways in the brain (you can find all of those structures here). The team says the results are encouraging, and call for “larger-scale investigations” in the relationship between alcohol and aggression using larger samples and stronger doses.

“Doing so could eventually substantially reduce alcohol-related harm,” adds Denson.

The paper “The neural correlates of alcohol-related aggression” has been published in the journal Cognitive, Affective, & Behavioral Neuroscience.