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DURHAM, N.C. -– In the first human study to assess alcohol's effects on memory in young adults, researchers at Duke University and the Durham VA Medical Center found that just two drinks can dampen the ability of college-age students to learn and remember new information, but the same amount has little effect on a person aged 25 to 29.

The researchers say this suggests there is a critical window of time in early adulthood when the brain becomes less sensitive to alcohol's memory-impairing effects. Prior to that period, alcohol appears to inhibit learning and memory in young brains but not in adult brains, according to five years of animal research and their latest human study.

Results of the human study, funded by the U.S. Dept. of Veterans Affairs, are published in the October issue of Alcoholism: Clinical and Experimental Research. 

The difference in brain effects arises because alcohol disrupts a key memory process in the brain's "hippocampus" much more powerfully in the young brain than in the adult brain, said Scott Swartzwelder, a Duke University Medical Center neuropsychologist and research scientist at the Durham VA Medical Center.

According to more than a dozen animal studies, just a single drink impaired learning and memory in young rats but had no effect on memory in adult animals. Now, they hope their pilot study in humans will convince young people to abstain where legal and moral threats have failed.

In the human study, the research team administered the equivalent of about two drinks over an hour's time to 12 subjects, half aged 21 to 24, and half aged 25 to 29. After the dose of alcohol, the younger group performed 30 percent worse than the older group on a memory test of recalling words from a list read aloud 20 minutes earlier. The younger group also performed worse on a memory test requiring subjects to draw a linear figure shown to them earlier.

While alcohol decreased the performance of all subjects in their study, there was a strong correlation between age and ability to learn and recognize the words after a dose of alcohol, the report said. Yet there was no difference in the two groups' blood alcohol levels or how their bodies metabolized the drug.

"Quite simply, the younger the age, the worse they performed on the memory tests when given the equivalent of two drinks," said Shawn Acheson, assistant professor of psychology at Western Carolina University and a researcher at the Durham VAMC who was part of the research team. "If alcohol's effects varied that much within such a narrow age range, then there's a compelling reason to believe its effects are even stronger in adolescents and children." Legal and ethical reasons prevented them from studying people under 21, he said.

Researchers say they don't know why the age difference exists, but there appears to be a critical period during which the brain becomes less sensitive to alcohol's memory-impairing effects.

What they do know is a primary brain region where alcohol disrupts the formation of memory. From their extensive research in rats, the researchers have shown that alcohol blocks the action of a specific nerve cell receptor in the brain's hippocampus, the region where new information is processed before it can be committed to permanent memory. When the function of these hippocampal "NMDA" receptors is impaired, the cells cannot receive electrical messages from neighboring nerve cells, thereby preventing the acquisition and processing of new information. Alcohol causes this type of impairment, their studies show.

While the researchers studied only the acquisition of new memory, they suspect that any information housed in the hippocampus may be at risk for loss, Acheson said. That's because the consolidation of memory in the hippocampus is a process that takes time – up to three years before data is committed to permanent memory, according to widely accepted neurologic data spanning 40 years.

"Because of the way alcohol affects hippocampal function, the strategy of studying on Saturday and then drinking on Saturday night is exactly the wrong combination," Acheson said. "The information you learned Saturday is being churned through the hippocampus even when you're not paying attention to it. If your hippocampal function is inhibited, then the information won't be converted to memory."

What worries researchers is the small amount of alcohol required to initiate this impairment. As little as two drinks – about .07 percent of blood alcohol and not enough to be considered legally intoxicated to drive – was enough to impair memory. Yet national statistics show that young people routinely drink far greater amounts of alcohol.