Understanding the neuroscience of drunken aggression might help to reduce alcohol-related crime. New research uses brain scans to investigate why people can become aggressive after they’ve had a few.

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Why do we tend to get aggressive when we drink?

The new study was led by Thomas Denson, of the University of New South Wales in Sydney, Australia, and the results are now published in the journal Cognitive, Affective, & Behavioral Neuroscience.

As Denson and colleagues write in their paper, inebriation is involved in around half of all violent crimes.

Homicide, physical and sexual assault, domestic violence, and child abuse are only some of the crimes associated with heavy alcohol use.

However, combined with an aggressive predisposition, even just a drink or two can incite violence. And previous neuroscientific studies have attempted to explore the brain mechanisms behind this phenomenon.

Most studies have hypothesized that changes in the brain’s prefrontal cortex — one of the most highly developed areas of the brain, it coordinates decision-making, judgment, and emotional control, among other things — may account for alcohol-induced aggression.

However, imaging data was mostly insufficient. So, Denson and team set out to fill this gap in our understanding by placing 50 young men inside an MRI scanner to study what goes on in their brains after they’ve had a drink or two.

The 50 participants were divided into two groups: one whose members received up to three vodka drinks, and one whose members received alcohol-free, or placebo, drinks.

Inside the MRI scanner, the young men had to complete a modified version of the so-called Taylor Aggression Paradigm, which is a traditional tool that has been used for the past half a century to assess levels of aggression in a retaliatory scenario.

The brain scans revealed that activity in the prefrontal cortices of those who had the alcoholic drinks was considerably diminished compared with that of those who had the placebo drinks.

The same effect also was seen in brain areas associated with reward processing (that is, the so-called caudate and ventral striatum), whereas in the hippocampus (a brain area dealing with learning and forming new memories), the researchers noted increased activity.

“These results support theories that posit a role for prefrontal cortical dysfunction as an important factor in intoxicated aggression,” write the researchers.

Denson further explains the findings, saying, “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.”

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

We encourage future, larger-scale investigations into the neural underpinnings of alcohol-related aggression with stronger doses and clinical samples. Doing so could eventually substantially reduce alcohol-related harm.”

Thomas Denson

Such a reduction in alcohol-related harm would be very welcome. In the United States, a recent survey reported that around 40 percent of those imprisoned for violent crimes were inebriated when they committed them.

Also, some experts maintain that alcohol is involved in more homicides than cocaine and heroin combined.