Boozing it up in adolescence contributes to risky behavior in adulthood, according to a new study with rats. Some researchers suspect that the same is true for people, but they've had a hard time establishing whether adolescent drinking makes people prone to risk-taking or whether risk-prone people are simply more likely to start drinking as teenagers. Although the new work doesn't settle the issue, it bolsters the case that early alcohol use can cause lasting changes in behavior.
Some of the best data available show that people who start drinking as adolescents and drink more heavily then are more likely to have problems with alcohol and drug abuse later in life, says Ilene Bernstein, a neuroscientist at the University of Washington, Seattle, and the senior author of the new study. But those studies have fallen short of determining cause and effect, Bernstein says. To get around this pitfall, she and her colleagues turned to rats, assigning individuals from a genetically identical strain to either drinking or teetotaling groups.
Although rats don't voluntarily like to drink alcohol, the researchers found they could entice the rodents with spiked gelatin--the murine equivalent of the Jell-O shots beloved by college students everywhere. Adolescent rats assigned to the drinking group had access to the stuff for 20 days. They consumed the equivalent of "multiple, multiple drinks" a day but spread their drinking over many hours and never appeared visibly drunk, Bernstein says.
To test the rats' propensity for risk, the researchers adopted a gambling task used by psychologists to study risk-taking in people. The animals learned that pressing one lever produced small but certain rewards in the form of small sugar pellets and an adjacent lever yielded bigger rewards--more pellets--but paid off less frequently. The researchers rigged the game so that in some testing sessions choosing the certain reward was the best overall strategy, while in other sessions the "risky" lever yielded the greatest overall payoff.
Teetotaling rats figured out the game over the course of a testing session and adjusted their strategy accordingly. Rats in the alcohol group also quickly learned that pressing the levers could lead to food, which Bernstein says argues against a general learning impairment. But 3 months after their last drink, they always preferred the risky lever, even when they payoff was poor, the researchers report this week in the Proceedings of the National Academy of Sciences.
"It's a good step forward," says Martin Paulus, a psychiatrist who studies addiction and decision-making at the University of California, San Diego, and the Veterans Affairs San Diego Health Care System. Paulus says the findings provide solid evidence that alcohol use in adolescence can cause lasting effects on adult behavior. He notes that the genetic and environmental influences at play are far more complex in people, but he thinks the study will facilitate further investigation of how early alcohol exposure could alter decision-making circuitry in the brain.
One possibility, Bernstein says, is that brain regions such as the prefrontal cortex, which plays an important roles in decision-making and is still maturing in human teenagers, are particularly sensitive to the effects of adolescent drinking: "Alcohol for some reason is very toxic to developing nervous systems."