Drunk drivers are good homing pigeons, but if they try a new route, trouble follows. New research hints at why: Alcohol dampens activity in a part of the brain that monitors people's performance and lets them know when they're making mistakes.
Even before people realize they've made an error, the anterior cingulate cortex (ACC) revs up. The size of the signal predicts how vigorously people respond to their mistakes. So it seems this piece of gray matter starts pinging to let people know when they need to adjust their behavior to avoid mistakes.
Alcohol can lead to big mistakes. To test whether that's because it puts a damper on the ACC, a team led by cognitive neuroscientist K. Richard Ridderinkhof of the University of Amsterdam in the Netherlands assembled a group of "social drinkers"--people who imbibe one to three drinks a day. Two groups of male volunteers drank screwdrivers (orange juice and vodka) until their blood alcohol concentrations registered 0.04% or 0.10%. The control group drank plain orange juice, although all the frosty beverages were laced with peppermint to hide the taste of alcohol.
The researchers then tested the men with an identification task: A computer screen displayed arrows for a few seconds, and the men had to push a button according to which direction a particular arrow pointed. The researchers found that when sober volunteers made obvious mistakes, they slowed down on the next round. But both groups of imbibing men failed to slow down after making mistakes. In addition, the signal coming from the ACC wasn't as strong, the team reports online 7 November in Science Express. "The ACC was not noticing the errors," says Ridderinkhof.
Whereas previous studies focused on how booze affects the entire brain, the new findings suggest that alcohol might impair a very specific component of brain activity, says cognitive neuroscientist Sidney Segalowitz of Brock University in Ontario, Canada. The findings reveal that in some cases, people under the influence don't respond to mistakes by being more careful. Instead, they don't even notice.