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Dramatic mood shifts while drinking alcohol are normal, but for some of us, booze takes us down a path toward nasty, belligerent, and downright aggressive behavior. By studying brain scans of drunk men, Australian scientists have pinpointed the parts of our brain that go weak when we drink, making us meaner than usual. But like so many aspects of human psychology, it’s a lot more complicated than that.

Our prefrontal cortex—the part of the brain responsible for planning, personality, and moderating social behavior—dozes off when we drink alcohol, according to new research published this week in Cognitive, Affective, & Behavioral Neuroscience. This isn’t the first time that the prefrontal cortex has been implicated in alcohol-fueled aggression, but the University of New South Wales scientists who conducted the study produced tangible empirical evidence in the form of high-quality fMRI brain scans to bolster this assumption.

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Approximately 35 percent to 66 percent of violent crimes involve alcohol, ranging from murder and physical assaults to sexual violence and domestic abuse. Less severely, booze makes us a bit nastier than normal; our criticisms become more cutting, our anger feels more palpable, and our tolerance for frustration evaporates. We lash out when we’re drunk, and drunk people lash out at us in return.

On its own, however, alcohol doesn’t just suddenly make us violent or mean. It’s when we combine booze with tense, unwanted, or potentially hostile situations—and with a personality that tends towards “dispositional aggressiveness” (i.e. an urge towards forceful or violent behavior)—that meanness sometimes trickles through. Alcohol acts as a lubricant that facilities this underlying aggression. The new study was an effort to learn more about this “lubricant,” where it’s located in the brain, and how it works.

For the study, lead researcher Thomas Denson used functional magnetic resonance imaging to measure blood flow to the brain. Previous research had pinpointed the prefrontal cortex as the area responsible for heightened aggression while drinking, but Denson wanted to see this effect in action. As noted, the prefrontal cortex is responsible for planning complex behavior, personality expression, decision making, and moderating social behavior. These tasks collectively make up our “executive function,” allowing us to discern between conflicting thoughts, distinguish between bad and good, better and best, same and different, and—very importantly—it allows us to comprehend the consequences of our actions.

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Empirical evidence in the form of brain scans are lacking in this area, which is where Denison’s experiment comes in. For the study, his team recruited 50 healthy young men between the ages of 18 and 30, none of whom knew that alcohol would be involved when they signed up for the study (sorry ladies, hopefully the next study will involve women—cuz last I checked women (1) have prefrontal cortexes, (2) drink, (3) and can also get mean). Potential candidates for the study were omitted if they had pre-existing alcohol abuse problems, reported poor physical or mental health, were on meds that don’t agree with alcohol, were averse to booze, and didn’t drink three or more times a month, among other screening factors.

The participants were given two drinks containing vodka or a placebo drink without any booze in it. Mildly buzzed, the participants were asked to play a competitive reaction-time task while inside the fMRI scanner—a task that’s been used for decades by scientists to measure aggression. This game is super frustrating because the winner of each round gets to send a blast of unpleasant noise to the loser. After a while, the whole thing starts to get a bit retaliatory—especially when considering the volume can be controlled by the winner. In this study, however, the participants were told that they were competing against other humans, but in reality they were playing against two computers.

As this was happening, the scientists were busy scanning their brains, paying close attention to the part of the game when participants have to decide about whether to be aggressive or not in terms of the retaliation. Denson’s team could visually see which areas of the brain were active when the task was performed, and then compare the differences between those who drank alcohol to those who did not.

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Looking at the scans, the participants showed no unusual neural response while they were being provoked. But it was the very moment when they chose to act aggressively that the scientists saw a discernible dip in prefrontal cortex activity—and only among those who drank alcohol. Normally, our prefrontal cortex puts the brakes on aggressive behavior. But it also happens to be the part of the brain that pulls the trigger on aggression. Sometimes, the presence of alcohol upsets this delicate balancing act, shifting our decision-making faculties towards aggressive behavior.

“The findings of this study add support to theories regarding alcohol-related aggression that have proposed alcohol would have effects on the brain structures identified in this study, especially the prefrontal cortex,” Brian M. Quigley, an addictions expert from the University at Buffalo, SUNY, who wasn’t involved in the study, told me. “Alcohol affects decision making by decreasing one’s attention to inhibitory cues, making one act more impulsive or immediately responsive to what is right in front of them—a process known as alcohol myopia.”

As an example, Quigley points to an all-too-common scene in which a drunk person gets accidentally bumped by another person, and they start to fixate on that immediate moment—the unwanted push—and respond before thinking about other relevant factors, such as having the crap pounded out of them, getting thrown out by the bouncers, or having to deal with police.

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“The prefrontal cortex is where we process inhibitory information, so showing decreased prefrontal cortex activity when intoxicated and engaging in aggressive behavior makes perfect sense and fits our models of intoxicated aggression,” he said.

Overall, Quigley likes the new study, but he says there are some limitations worthy of note. The study (for ethical reasons) excluded people with alcohol problems, but these “are often the individuals we are most interested in because those with alcohol problems are the ones most likely to be involved in alcohol-related aggression,” he said. That’s a limitation to the study’s findings, he said, but it doesn’t invalidate them. He also said the reaction-time aggression test is a limited way of measuring aggression, as some researchers (himself included) question if participants are really intending to harm the other person in the game.

He also pointed out that not everyone who drinks gets aggressive, and not all people who are aggressive drink—but booze can lower a person’s threshold for becoming aggressive. For people with a tendency towards aggression or “meanness,” Quigley says it’s important to not drink as much, or at all.

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“As the current article has shown, even a low dose of alcohol can promote aggression in the right situation and in people prone to it,” he told me. “So the second-best advice is if you are drinking and find yourself in a situation where you might be driven to act aggressively by things going on in the environment, remove yourself to a different environment.”

As already pointed out, alcohol causes us to fixate on immediate cues in the environment, so if those cues promote peaceful, happy, or non-aggressive behavior, we aren’t likely to be aggressive.

“To avoid aggression when drinking, drink in an environment in which there won’t be instigation to be aggressive,” said Quigley. “Someone who has had problems with intoxicated behavior before and plans to continue drinking may need to drink in different places or with different people in order to avoid conflict.”

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Got it? Please drink responsibly, choose the rights friends and environment, and be self-aware if you’re prone to aggression.

[Cognitive, Affective, & Behavioral Neuroscience]