New research indicates that even moderate drinking by adolescents on a regular basis can cause potentially lasting changes to the part of the brain that affects memory.
Much of the previous research focused on behavioral effects of alcohol consumption. The new study looked at long-term effects of “intermittent” drinking on the circuitry of an adolescent brain.
The study investigated the biological mechanisms behind these long-term effects, says Scott Swartzwelder, the lead scientist on the new study, published Monday in the journal Alcoholism: Clinical & Experimental Research, and a professor of psychiatry at Duke University in Durham, N.C.
Dr. Swartzwelder is careful to say “adolescent” instead of “teen.” As a society, we think that adolescence is over once someone hits 18, he says. But from a neuroscientist’s perspective, the brain isn’t fully developed until age 25 and can exhibit these negative effects of alcohol consumption until then, he says.
Dr. Swartzwelder’s team gave rats 10 doses of alcohol over their 16-day period of adolescence in a roughly “two days on, two days off” pattern that imitates how adolescents drink intermittently, he says. The rats were given doses that were the equivalent of “maybe a solid five drinks” for humans, not enough to cause them serious impairment, Dr. Swartzwelder says.
Compared with the cognitive functioning of a control group that didn’t get any doses, the rats exposed to alcohol had worse functioning in the hippocampus, a brain region that is responsible for learning and memory.
In both rats and humans, the brain’s synapses, or connections between nerve cells, become stronger as they recall memories or learn something new. This mechanism is called “long-term potentiation,” and young people, who tend to learn more quickly, typically have the most LTP. Dr. Swartzwelder found that the rats exposed to alcohol had more LTP than normal.
This seems counterintuitive, but “more LTP is not necessarily a good thing,” he says. “If it’s too easy to produce LTP in those circuits, they can become saturated and they can’t produce any more LTP for a while.” In humans, these changes would lead to poorer memory and slower learning, he says.
The oversaturation of LTP likely happens because alcohol changes the physical structures of the branches of the nerve cells, called dendritic spines. In addition, if brain cells get much too LTP, they can experience toxicity and become more vulnerable to death.
Dr. Swartzwelder’s team is now doing follow-up research into how being exposed to alcohol during adolescence affects LTP. “If we know more about the mechanism of an effect, it gives us the opportunity to target treatments,” he says.