Seeing the adult in the infant

Ever wished you could peek into a crystal ball and see your baby’s future? A three-decade-long study that followed 14-month-old infants into adulthood could be quite enlightening.

Researchers found that toddlers who displayed behavioural inhibition – cautious and fearful behaviours when exposed to unfamiliar people, objects and situations – became more reserved and introverted and less socially active as adults.

And as teens, those that showed more intense brain activity after making mistakes in a computer task were more likely to develop symptoms of anxiety and depression, reports the study published in the journal Proceedings of the National Academy of Sciences.

“Children show different behavioural styles very early in development,” explains lead author Alva Tang from the University of Maryland in the US.

“Whether these behaviour differences predict who children become as adults and how early we can foretell their life course patterns have been longstanding questions.”

Behavioural inhibition is one of the most well-characterised temperaments in infancy, and it is known to affect social and emotional functioning throughout childhood. Even non-human animals show similar neophobic and timid tendencies. 

In humans, it is associated with a four- to six-fold increase in risk of developing anxiety disorders, particularly social anxiety – but as the authors note, this only applies to 40% of people. 

In the most ambitious effort to explore this to date, and the first to investigate it in the first year of life, senior author Nathan Fox launched the longitudinal study in the early 1990s, recruiting a cohort of 165 infants at four months of age. 

At 14 months, the infants were videotaped while exposed to three unfamiliar situations: being approached by an adult stranger, an unfamiliar playroom and a toy robot as tall as them. 

Blinded observers then coded how long it took them to approach or adapt to the situations and how close they stayed to their mothers.

At age 15, the participants completed a computer task while an electroencephalogram measured their brain activity in response to monitoring errors. Then, as 26-year-olds, they completed self-report questionnaires to assess their personality, mental health and social functioning. 

The finding that behaviourally inhibited infants became more reserved, introverted adults with lower social functioning extends other studies that tested children from three to six years of age.

Various theories propose this occurs due to interactions between infant temperament and the environment.

“As people age, personality might become increasingly stable due to the accumulation of and reinforcement from consistent experiences selected or created by the individuals,” the authors write.

As an example, they suggest parents of behaviourally inhibited children might be overprotective, thus reinforcing the child’s temperament and social interactions. 

Children who are fearful of new social situations may avoid them and thus prevent opportunities for social learning and friendship building. 

Intriguingly, the study didn’t find that early inhibition was related to career and education or romantic relationship outcomes, adding to other inconclusive findings in these regards. 

Tang suggests several possible reasons for this, including methodological or generational differences.

“Alternatively,” she says, “it could mean that even though behaviourally inhibited infants have worse social functioning in some domains, they are by and large able to function effectively in society.”

By revealing neural activity associated with anxiety disorders in adulthood, the study also gives insights into risk versus resilience, providing an opportunity to intervene.

“These findings highlight the enduring nature of early temperament, which shapes long-term personality and wellbeing,” Tang says, “and suggests that neurophysiological markers could help identify individuals who are most at risk for internalising psychopathology in adulthood.”