Weaker Gut Instinct Makes Teens Open to Risky Behavior

Making a snap decision usually means following your initial reaction -- going with your gut. That intuitive feeling sprouts from the limbic system, the evolutionarily older and simpler part of the brain that affects emotion, behavior and motivation.

But during adolescence, the limbic system connects and communicates with the rest of the brain differently than it does during adulthood, leaving many adolescents vulnerable to riskier behaviors, according to Duke University researchers.

"We know adolescence is a time of profound social change. It's also a profound time for risk-taking -- a time period when peer influence is more important," said Kevin LaBar, a professor in the Duke Center for Cognitive Neuroscience. "This is when we start establishing independent relationships with adults, and some of those relationships are going to be influenced by how trustworthy those people are. It's important in these relationships to evaluate who you can and can't trust."

To date, there has been significant research into how the adult brain processes and judges trustworthiness, said LaBar, who is also a member of the Duke Institute for Brain Sciences. But few studies look at the adolescent brain's ability to evaluate trustworthiness.

The study, which appears in the March 2014 Social Cognitive and Affective Neuroscience, examines this capability in adolescent girls, ages 10 to 20. LaBar said boys weren't included in the study because they mature at a slower rate than girls.

The research team enrolled 43 girls and showed each 34 pictures of adult faces in extremely fast (50-millisecond to 100-millisecond) glimpses while recording their reactions in real time using functional MRI (fMRI) brain scanning. After each flash, the images were immediately scrambled to prevent the girls from developing any lasting visual memory of a face, LaBar said.

After each image, participants rated the face as very untrustworthy, untrustworthy, trustworthy or very trustworthy. The fMRI whole-brain scans recorded where blood flow and oxygen increased in the brain for each picture. Areas of increased activity helped the researchers isolate the regions of the brain responsible for processing social and emotional information from faces.

Existing research from Princeton University on how adults process trustworthiness helped LaBar's team pinpoint the facial features that prompted feelings of mistrust in these participants. According to the research, faces with downward-turned mouths and furrowed eyebrows are among the most untrustworthy. In contrast, faces with U-shaped mouths and wide-set eyes rank among the most trustworthy.

Based on the fMRI results, the components of the limbic system known as the amygdala (which evaluates negative emotions) and insula (which plays a role in gut-level decision making) were the most active for the faces participants rated as untrustworthy. Among all ages, the right amygdala showed high levels of activity when presented with an untrustworthy face. Other spots within the amygdala and insula also demonstrated increased activity in these instances, peaking among the 13- to 15-year-old participants.