Heavy drinking during adolescence may lead to structural changes in the brain and memory deficits that persist into adulthood, according to an animal study published October 29 in The Journal of Neuroscience. The study found that, even as adults, rats given daily access to alcohol during adolescence had reduced levels of myelin -- the fatty coating on nerve fibers that accelerates the transmission of electrical signals between neurons. These changes were observed in a brain region important in reasoning and decision-making. Animals that were the heaviest drinkers also performed worse on a memory test later in adulthood. The findings suggest that high doses of alcohol during adolescence may continue to affect the brain even after drinking stops. Further research is required to determine the applicability of these findings to humans.

According to the World Health Organization, a growing number of adolescents and young adults around the world engage in binge drinking, the consumption of four (five for men) or more drinks over approximately two hours. Previous research in humans has shown an association between heavy episodic (binge) drinking in adolescence, changes in myelin in several brain regions, and cognitive impairments in adulthood. However, it was unknown whether alcohol was behind these brain and behavioral differences or if predisposing factors could explain the findings.

In this study, Heather Richardson, PhD, her graduate student Wanette Vargas, BA, and colleagues at the University of Massachusetts, Amherst, compared myelin in the prefrontal cortex -- an area of the brain that is vital to reasoning and decision-making -- in young male rats given daily access to either sweetened alcohol or sweetened water for two weeks. Animals that drank alcohol as adolescents had reduced myelin levels in the prefrontal cortex compared with those that drank a similar amount of sweetened water. When the researchers examined the alcohol-exposed animals several months later, they found that the animals continued to display reduced myelin levels as adults.

"Our study provides novel data demonstrating that alcohol drinking early in adolescence causes lasting myelin deficits in the prefrontal cortex," Richardson said. "These findings suggest that alcohol may negatively affect brain development in humans and have long-term consequences on areas of the brain that are important for controlling impulses and making decisions."

The researchers also examined how adult animals that binged on alcohol as adolescents performed on a test to assess working memory, the ability to hold on to information for a short period. The more alcohol the rats consumed over the two-week period as adolescents, the worse they performed on the working memory task as adults.

"This study suggests that exposure to high doses of alcohol during adolescence could exert lingering, if not permanent, damage to selective brain fibers," said Edith Sullivan, PhD, who studies the effects of alcohol on brain function at Stanford University and was not involved with this study. "This damage might underlie persistent compromise of cognitive functions involved in learning and render youth vulnerable for later development of alcohol use disorders."