It’s the classic chicken or egg type question: Do activation patterns in the brain predict the onset of heavy drinking behaviors, or is it the heavy drinking itself that leads to neural abnormalities? The answer appears to be a little of both as adolescents who initiate heavy drinking have different brain activation before the onset of drinking, while heavy drinking leads to further neural responses over time, according to a study published in the September issue of the Journal of Studies on Alcohol and Drugs.

“The findings suggest neural activation as potential biomarkers for youth at risk to transition to heavy drinking,” wrote the researchers, led by Lindsay M. Squeglia, PhD, of the University of California, San Diego, department of psychiatry.

The study was conducted in two parts. The first used functional MRI (fMRI) visual working-memory (VWM) data from 40 subjects, ages 15 to 19, half of whom were heavy drinkers and half of whom served as controls. This study identified brain regions affected by heavy alcohol use in adolescence. The second used longitudinal fMRI VWM data from a group of 40 subjects, ages 12 to 16, who were imaged before the onset of drinking and again on the same scanner three years later.

About half of the participants in the second part transitioned into heavy drinking over the three-year period; fMRI imaging at baseline in this group already showed less response in brain regions linked to heavy drinking. "Overall, these results fit with an emerging model suggested from prior longitudinal behavioral and cross-sectional imaging studies indicating that youth at risk for heavy drinking show reduced activation to cognitive challenges yet intact performance before the onset of heavy drinking compared with low-risk youth,” wrote the authors.

“After heavy drinking started, activation levels tended to be higher, yet performance remained intact, compared with nondrinkers,” they continued, noting previous research suggests the brain is initially able to compensate for neural abnormalities following heavy drinking with increased activation.

“At the point these teens began drinking heavily, the fMRI data revealed greater parietal and frontal activity during a spatial working memory task in heavy drinkers versus light drinkers, despite equivalent performance on the tasks and after considering their brain activation patterns before drinking started,” Squeglia said in a release.

But there are limits to how well the brain can cope. Over time, adolescents who initiated heavy drinking exhibited less efficient processing of information, according to the authors.

Heavy drinking was defined as episodes of consuming four or more drinks on an occasion for females, and five or more for males.

The brain areas shown on fMRI to be most affected by heavy drinking were the parietal lobe, which processes spatial information, and the frontal lobe, which is involved with short-term memory tasks, planning and organization.

“Our results suggest there could be a pre-existing vulnerability, and could provide clues to the biological origins of problem drinking,” said Squeglia.