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Infant temperament predicts introversion in adulthood

The researchers studied how behavioral inhibition in infancy affected outcomes in young adulthood. NiDerLander / iStock / Getty Images Plus

We each have different temperaments that are fairly stable over time. Temperament is the biologically based way a person tends to emotionally and behaviorally respond to the world. Temperament during infancy can serve as the foundation for personality over time.

One type of temperament, called behavioral inhibition, is characterized by cautious, fearful behavior toward unfamiliar people, objects, and situations. Behavioral inhibition is relatively stable across toddlerhood and childhood. Children with behavioral inhibition are at elevated risk for developing so-called internalizing conditions such as social withdrawal and anxiety disorders.

The brain’s error monitoring system is thought to play a role in such conditions. This can be seen on EEG brain recordings. Negative dips show up when a person makes an error on a computerized task. This is called error-related negativity, or ERN. ERN reflects how sensitive a person is to their errors. A larger ERN has been associated with behavioral inhibition, while a smaller ERN has been linked with conditions such as impulsivity and substance use.

To investigate whether behavioral inhibition in infancy can predict personality traits in adulthood, a research team led by Drs. Daniel Pine at NIH’s National Institute of Mental Health (NIMH) and Nathan Fox at the University of Maryland recruited 165 infants at 4 months of age and assessed them for behavioral inhibition based on observation at 14 months.

When the infants were 15 years of age, the researchers recorded ERN on EEGs. The participants then returned at age 26 for assessments of psychopathology, personality, social functioning, and education and employment outcomes. Results appeared on April 20, 2020, in Proceedings of the National Academy of Sciences.

The team found that behavioral inhibition at 14 months of age predicted, by age 26, a more reserved personality, fewer romantic relationships, and lower social functioning with friends and family. It also predicted higher levels of internalizing behaviors in adulthood, particularly among those who also displayed larger ERN signals at age 15. Behavioral inhibition was not associated with education and employment outcomes.

“We have studied the biology of behavioral inhibition over time, and it is clear that it has a profound effect influencing developmental outcome,” Fox says.

More research is needed to see whether these findings apply more broadly to diverse populations. Most of the participants in the study were Caucasian and grew up in the middle to upper-middle classes.