New imaging studies from Yale show that when the human brain is under the influence of alcohol, different areas of the brain are impaired under high and low levels of alcohol.
Godfrey Pearlson and Vince Calhoun, researchers in the Department of Psychiatry at Yale School of Medicine, used a statistical method to sort areas of the brain affected when persons were administered a placebo or two different doses of alcohol. The seven men and two women then "drove" using a simulated driving skill game.
"What we found is that when people were really intoxicated, they drove like they were really intoxicated and in a real vehicle," Pearlson said. "They speeded up, especially on corners, where most people slow down, and crashed more often into other vehicles." When mildly intoxicated, but below the legal alcohol limit, he said, the drivers seemed aware of the fact that they were impaired and corrected for the deficit. The researchers also found that alcohol had a profound effect on some, but not all, brain circuits activated in sober driving.
The areas most profoundly affected by alcohol were the orbital frontal and anterior cingulate areas, which help control motor functions. The medial frontal regions of the brain involved in making decisions, and working memory, were not affected until the person was beyond the legal limit of intoxication. A function of working memory might be to find one's way home, the researchers said.
Impairment of the cerebellum area of the brain, which related strongly to speeding, was clearly correlated with the alcohol dose. Changes in the frontal and parietal cortex, which govern alertness and attention, were correlated with weaving while driving.
The highest blood alcohol level was 0.1 and the lowest was 0.05. Drivers are considered legally drunk when their blood alcohol level is 0.08.