The adult brain that was awash in alcohol during its formative years looks different and acts differently than an adult brain that skipped the youthful binge drinking, says a new study conducted on rats.
All grown up, the brain exposed to periodic alcoholic benders during adolescence and young adulthood shows persistent abnormalities in the structure and function of the hippocampus, the region most closely associated with learning and memory. The specific changes seen in adult rats who were regularly plied with alcohol during the brain's development generally result in memory problems and neuropsychiatric impairments such as attention and judgment problems and ability to learn new skills.
To make matters worse, the physical changes in hippocampal brain cells appear to make them more-than-usually vulnerable to injury from trauma or disease.
The study was published Monday in the journal Alcoholism: Clinical and Experimental Research.
The National Institute on Alcohol Abuse and Alcoholism defines binge drinking as a pattern of drinking that brings a person's blood alcohol concentration, or BAC, to 0.08 grams per deciliter or above. This typically happens when men consume five or more drinks, and when women consume four or more drinks, in about two hours.
According to a 2005 study by the Department of Justice's Office of Juvenile Justice and Delinquency Prevention, about 90% of the alcohol consumed by youth under the age of 21 in the United States is in the form of binge drinks.
The new research suggests that the still-developing brain of an adolescent or young adult is uniquely sensitive to levels of alcohol that are consistent with binge drinking. Discouraged parents may find their prohibitions against underage alcohol consumption often fall on deaf ears. But the new research offers some solid scientific backing for continuing to urge high-school and college-aged youths not to abuse alcohol.
"In the eyes of the law, once people reach the age of 18, they are considered adult, but the brain continues to mature and refine all the way into the mid-20s," said lead author Mary-Louise Risher, a post-doctoral researcher in the Duke Department of Psychiatry and Behavioral Sciences.
"It's important for young people to know that when they drink heavily during this period of development, there could be changes occurring that have a lasting impact on memory and other cognitive functions."
Over a 16-day period during their adolescence, male lab rats were plied with enough alcohol to approximate a binge-drinking episode on 10 separate occasions. The amount of alcohol given to the young rats was enough to cause impairment - a buzz - but not enough to cause them to nod off or pass out. The hard-partying young rats were then returned to their normal living conditions for 24 to 29 days, during which they were allowed to mature normally into adulthood.
When researchers compared the cells of these rats' hippocampal area to those of rats who matured without exposure to alcohol, they saw neurons with stunted and misshapen connections to other neurons. When stimulated, those neurons over-reacted, disrupting the delicate balance between excitement and inhibition that makes the brain's cells function properly.
That hyper-sensitivity came as a surprise to the study's authors. Essentially, the researchers concluded, the brains of the adult rats that had binged in adolescence looked and acted like those of immature rats. But they weren't immature in a stronger, faster, more youthful way; they were immature in a way that suggested they might never likely settle down and function in ways that allow learning to proceed and memories to be built, stored and maintained efficiently.
"At first blush, you would think the animals would be smarter," said the study's senior author Scott Swartzwelder, a professor of psychiatry and behavioral sciences at Duke University. "But that's the opposite of what we found."
In their immature and highly excitable state, the memory circuits affected by early binge drinking are quickly overwhelmed, and learning must shut down for a time so the brain can catch up, said Swartzwelder.
This immature quality of the brain cells might be associated with behavioral immaturity, said Risher. In addition to changes in the shape and projections of hippocampal neurons, the authors' colleagues - researchers in the Neurobiology of Adolescent Drinking in Adulthood consortium - have shown structural changes in other brain regions that control impulsiveness and emotionality.
"It's quite possible that alcohol disrupts the maturation process, which can affect these cognitive function later on," said Risher. Ongoing studies will explore that possibility further, she said.