WEDNESDAY, April 30, 2008 (HealthDay News) -- Alcohol can make people frisky, chatty and, as any bouncer knows, feisty.
Now, a new brain scan study shows drinking actually dampens the biological ability to feel fear.
When people drink, these lowered fear levels can lead to liquor-fueled courage that can ultimately make people more aggressive, explained study co-author Dr. Daniel Hommer.
"You're less likely to feel afraid, and you're also less likely to run away or to avoid conflict," said Hommer, chief of the section on brain imaging at the National Institute on Alcoholism and Alcohol Abuse.
Using a technology known as functional MRI, researchers scanned the brains of 12 subjects as they received alcohol or a saline solution intravenously.
All the subjects -- an average age of 26 -- were social drinkers, meaning they typically drank every week but not every day. They drank an average of 1.9 days a week and 3.6 drinks per day on the day they drank.
Seven of the subjects were women and five were men; all were healthy. Each volunteer received both alcohol or the saline solution, on two separate occasions.
The subjects looked at images of human faces. Some images had neutral expressions, while others had scary looks designed to provoke a natural fearful response.
The threatening faces "are a cue that something is dangerous going on," Hommer explained.
The fMRI scanner, meanwhile, tracked the levels of activity in parts of the brain where emotions are processed.
The researchers found that alcohol boosted activity in the parts of the brain that deal with rewards, but it also dampened activity in areas devoted to fear.
"This helps us understand a little more about how the brain works, and how alcohol functions as a drug in the brain," Hommer said.
The findings were published in the April 30 issue of The Journal of Neuroscience.
Aaron White, an assistant professor of psychiatry at Duke University who studies alcohol abuse, said the study is "excellent" and smartly relies on intravenously administering alcohol, a technique that allows easy adjustments of the subjects' blood-alcohol levels.
In similar studies, White added, "researchers should be able to learn a great deal about how the effects of alcohol on the brain change with both age and increasing years of use."
Other scientists could also study what happens in the brain when alcoholics and nonalcoholics look at images associated with alcohol like beer cans, bars and alcohol ads.
Hommer said researchers are thinking about other possible studies. "The one thing that might immediately be useful is that you may be able to use this as a way to test out drugs designed to decrease people's tendency to abuse alcohol."
The researchers are already testing their approach in people who are heavy drinkers to see if there is any difference in how they react to alcohol, Hommer said. "People become tolerant to some of the effects of alcohol with repeated use, and we want to see if we can see that" in the brain.
The U.S. Centers for Disease Control & Prevention has more on alcohol use.