When it comes to avoiding risky behavior, the teenage mind isn't always hard-wired to make smart decisions — a fleeting short circuit that's primarily a result of biology.

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"There are changes in the brain that make young adults vulnerable," says Meghan Martz, Ph.D., a postdoctoral research fellow at the University of Michigan Addiction Center. "Although the brain's reward system develops and matures in early adolescence, the prefrontal cortex has a much slower maturation that actually continues into a person's early 20s."

In other words, the part of the brain associated with impulse control may not be ready to "put on the brakes" when presented with temptations such as drugs or alcohol, Martz says.

Another factor can contribute to trouble: Young people with a family history of substance abuse — where destructive behavior and its ripple effects might be observed for years — are more vulnerable to developing the habits.

But that risk isn't universal.

That's why Martz sought to find out why some young people who, despite environmental and genetic hazards, manage to be resilient against substance misuse.

Unlike other studies that focus on social and parental influences (or compare these youths with those from stable families), she mainly targeted neurological function within the affected subgroup.

"We wanted to see if there were differences within this group. It's important to dig a little deeper to identify reasons for variability in (levels of) substance use among young people with this vulnerability," Martz says.

Results of her study, published this month in Drug and Alcohol Dependence, affirm that point: Brain function plays an important role in determining whether youths abstain from drugs and alcohol.

Classifying behavior patterns over time

To reach that conclusion, Martz and her team used data from the Michigan Longitudinal Study — the world's longest-running high-risk study on the development of substance abuse — to examine 30 years of research following individuals from childhood to early adulthood.

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The new analysis examined 57 of the study's participants who completed functional magnetic resonance imaging (fMRI) brain scans and had a family history of substance use disorder.

Within that group, 36 were defined as high-risk. That means each reported weekly binge drinking (more than five drinks in a single occasion) and using marijuana at least once a month. Those habits were self-reported on at least two occasions between the ages of 17 and 26.

Alternatively, the remaining 21 people were considered "resilient." They didn't all necessarily abstain from drugs and alcohol but used them below the risk threshold.

"They were able to regulate their substance use," Martz says of the latter group. "They seem to be better equipped to rein in those urges that they might be susceptible to."  

After accounting for sociodemographic differences, the number of parents with a substance use disorder, and psychological factors related to impulse control and acting out, the researchers then reviewed neuroimaging scans to see what sets resilient people apart — and why some of their peers could be more prone to trouble.

Using the scans, "we're getting at a different level to see what's going on behind the scenes within the brain," Martz says.

Brain scans reveal impulse control

As part of the longitudinal study, participants already underwent periodic brain scans. A scan that took place when each person was near or about 20 years old was accompanied by tasks to measure impulse behaviors and reward-processing.

One, a test known as go/no-go, projects a series of letters with users instructed only to hit a button when they see a letter that isn't "X."

"It's harder than you think," Martz says. "It gets at that 'holding back' response, being able to control yourself."

The other, a monetary incentive delay task, was prefaced by announcing that cash could be won by hitting a button when a certain shape appears. Because users were instructed to hit the button as quickly as possible, "we wanted to look at how their brain responded to the anticipation they're going to get a reward," Martz says. 

Differences between the two groups were pronounced: Those resilient to substance misuse behavior showed heightened brain activation in the prefrontal cortex compared to higher substance-using individuals who performed the same tasks.

Findings could inform prevention efforts

Still, the brain scans also revealed that both groups showed no difference in processing the notion of a reward.

Taken alone, that could be concerning. After all, "substance use is a reward-driven behavior," Martz says.

SEE ALSO: Over Time, Marijuana Use Dampens Brain's Response to Reward

But it was the fact that resilient individuals are better able to regulate impulse control that could be the key to preventing destructive habits.

The data gleaned from their experience may provide a foundation not only for deeper neurological research but also how past and future findings could be applied to help those in need.

"The brain is complex — what more can it tell us about risk and resilience?" Martz says. "Learning from youth who are putting on the brakes and doing it well may help inform prevention efforts to boost self-control."

University of Michigan Addiction Treatment Services offers a comprehensive range of services to help treat mild to severe substance use disorders, as well as co-occurring mental health needs such as depression and anxiety. To schedule an appointment, call 734-764-0231.