Bartholow and his team measured the electrical activity in participants’ brains as pictures of black and white men and women were shown briefly on a computer screen, followed quickly by stereotypical traits such as “violent,” “lazy” and “musical” for blacks and “arrogant,” “uptight” and “wealthy” for whites. Participants were asked to decide whether words like these, along with control words, could ever be used to describe the people in the preceding pictures. On a small number of the trials, participants were signaled to withhold their response; in other words, they were to try to inhibit the tendency to associate black and white people with stereotype-related traits.

The researchers found that participants who consumed alcohol had trouble controlling their responses to the stereotypes listed after the pictures. This behavioral control difficulty was associated with a decrease in a particular brainwave, called the negative slow wave, which reflects the brain’s control over voluntary responses.

“These findings suggest that after someone has been drinking, he or she might be more likely to blurt out a racist comment or laugh at a racist joke, even though he or she would ordinarily not make such a comment,” Bartholow said.

In a more extreme case, Bartholow said it is possible that alcohol could lead someone to insult another person in a racist way, which could potentially provoke a physical altercation.

“Studying factors associated with inhibition of race bias from a neuroscience perspective is important because doing so can tell us a great deal about processes that unfold very quickly in the brain and that do not depend on conscious acts of control or individual differences to control prejudice,” Bartholow said.

The research was published this week in the Journal of Personality and Social Psychology.