(CNN) -- If you're reserved and anxious or depressed, you might want to call your mom and ask her what you were like as a baby.
Why, you ask? The temperament you had as an infant may have predicted your personality and social experiences as an adult, according to a recent study published in the journal Proceedings of the Natural Academy of Sciences.
After following 165 infants for three decades, they found that babies who were more behaviorally timid became more reserved and introverted adults. Brain activity that reflected how adolescents avoided or perceived their mistakes was associated with anxiety and depression in adulthood.
"It was really the combination of both information on a young child's behavior and a measure of brain function in adolescents that most strongly predicted all of these outcome measures and, in particular, measures of mental health disorders," said study author Dr. Daniel Pine, chief of the section on development and affective neuroscience in the US National Institute of Mental Health Intramural Research Program.
Inhibition levels vary
Temperament describes the consistent differences in infant behavioral and emotional reactivity that serve as foundations for our later personalities.
One behavioral trait we've all inherited throughout evolutionary history is inhibition. It protects us from potentially dangerous situations, but not every person's temperament is dominated by inhibition.
Babies with high levels of inhibition exhibit overly cautious, fearful and avoidant responses to unfamiliar people, objects and situations in comparison to uninhibited infants.
Inhibition is known to influence social and emotional functioning in childhood. Studies have shown that such children have difficulties with peer interactions, express social withdrawal and are at higher risk for anxiety disorders, including social anxiety.
Adulthood comes with new challenges. Generally in prior studies, when more inhibited children reached their 20s, they were more at risk for anxiety, depression, being socially uninvolved and substance-use disorders. They also took longer to work full-time jobs, leave their parents' home, find a romantic partner and become parents.
The influence of temperament on success and health
Researchers followed 165 infants for three decades to find whether infant behavioral inhibition shaped personality, relationships, career, educational success and mental health in adulthood.
In a lab setting, researchers observed the 14-month-old infants' behavior toward three situations: playing in an unfamiliar playroom, exposure to an adult stranger and a novel toy robot. The authors judged the infants' behavioral inhibition according to their hesitancy to interact with the situations and how long they stuck close to their mothers.
The authors knew that not every inhibited baby-turned-adult faced mental challenges. So once the participants reached 15, the authors recorded their brain activity while they completed tests in which they had to quickly identify letters and accurately respond.
Through the scan, the authors observed the brain's error monitoring system, which regulates error-related negativity, or how our brain responds when we make a mistake.
The ERN response happens very quickly within a 10th of a second — faster than you can even comprehend the meaning of your mistake, Pine said.
Reduced ERN is associated with externalized conditions that both the person and other people can see, such as impulsivity that leads to losing one's temper and fighting, or substance misuse, Pine said.
Heightened ERN is linked with more internalized disorders, such as anxiety and depression, and high levels of inhibition throughout childhood.
At age 26, 109 adults reported information about their personalities, mental health and sociodemographics.
Infants with higher inhibition became adults who didn't function as well with friends and family — they found it harder to talk to strangers and people of authority, and felt less in tune with loved ones.
Their temperaments didn't affect their relationship status or work or education success — in fact, the proportion of participants with bachelor's degrees (86%) was higher than the national average (35%). But these introverted adults did have fewer past relationships.
Heightened error sensitivity in adolescence was associated with higher levels of anxiety, social anxiety and depression as adults.
Everyone thinks negatively of their mistakes. But people with high error sensitivity are more sensitive to their mistakes and find them more threatening and important than they really are, Pine explained — so they become more upset, especially if other people witness their blunder.
In social situations, people with heightened error sensitivity might always be second-guessing themselves because they're concerned about how they might look to others or whether they'll say something wrong, said Andrea Chronis-Tuscano, who wasn't involved in the study. She's a professor of psychology at the University of Maryland and president-elect of the International Society for Research in Child and Adolescent Psychopathology.
That could be a reason why the participants with stronger error sensitivity had fewer relationships.
Can parents look for signs?
Can parents change a baby's temperament? Experts said you could try.
Pay attention to your children when they're young and watch for signs of reservation and worry, Chronis-Tuscano suggested. You can help them work to overcome and approach anxiety-provoking situations by encouraging them to realize potential positives and that their fears might be baseless.
"Whether parents sort of give the child that gentle nudge to approach situations that they might be a little bit leery of can actually influence whether kids who are classified as behaviorally inhibited in infancy go on to develop anxiety disorders or not," Chronis-Tuscano said.
There's nothing wrong with being reserved and introverted, Chronis-Tuscano said. It's only a problem when it interferes with your life. If anxiety is holding you back from accomplishing what you want to, you can look into cognitive behavioral therapy that might help you conquer your fears.
Both children and adults need the opportunities to see that social experiences might not end badly, which is why exposure therapy has been "the treatment of choice" for anxiety disorders, Chronis-Tuscano said.
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