Behavioural inhibition and shyness at infancy leads to a reserved, introverted personality by the time a person reaches their mid-twenties, new research shows.
US neuroscientists found that infants with ‘behavioural inhibition’ grew up to be reserved and have fewer human interactions aged 26.
Individuals who showed sensitivity to making errors at the age of 15, meanwhile, later had a higher risk for internalizing anxiety and depression.
The quarter-century-long experiment is evidence of the long-lasting impact of our internal processes at a young age, despite physical changes and years of life experience.
Temperament during the first year of life can have lasting effects into adulthood, according to the study authors
‘While many studies link early childhood behaviour to risk for psychopathology, the findings in our study are unique,’ said Daniel Pine, study author and chief of the National Institute of Mental Health Section on Development and Affective Neuroscience.
‘This is because our study assessed temperament very early in life, linking it with outcomes occurring more than 20 years later through individual differences in neural processes.’
Temperament is defined as the biological individual differences in the way people emotionally and behaviourally respond to the world, researchers said.
During infancy it serves as ‘the foundation of later personality’.
In particular, one type of temperament, called behavioural inhibition (BI), is characterised by ‘cautious, fearful, and avoidant behaviour toward unfamiliar people, objects, and situations’.
Behavioural inhibition (BI) in children is characterised by cautious, fearful, and avoidant behaviour toward unfamiliar people, objects, and situations
For the study, researchers followed 165 people – all recruited at 4 months of age between 1989 and 1993 – over the course of a quarter of a century.
The participants, both male and female, engaged in three different activities when aged 14 months, 15 years and 26 years to measure BI using different methods.
At 14 months of age, infants were videotaped while exposed to an adult stranger, an unfamiliar playroom and a novel toy robot.
They had their behaviours observed and recorded, including time before the toy was touched and time spent in proximity to their mother.
At 15 years, participants had their brain signals recorded as they made errors during a computer task, otherwise known as error-related negativity (ERN).
ERN is a negative dip in the electrical signal recorded from the brain following incorrect responses on the task and reflects the degree to which people are sensitive to errors.
A larger ERN signal is associated with internalizing conditions such as anxiety, while a smaller ERN has been linked with externalizing conditions such as impulsivity and substance use.
11 years later, at the age of 26, participants were recalled one more time to be surveyed about their personality, relationships, mental health and vocation.
Behavioural inhibition in infancy predicts a reserved, introverted personality at the age of 26, the study found
The study found that participants who showed high BI as infants were more likely to become introverted, reserved adults and to report lower interactions with family and friends aged 26.
High BI at 14 months of age predicted, at age 26, a more reserved personality, fewer romantic relationships in the past 10 years and lower social functioning with friends and family.
Having BI as an infant also predicted higher levels of ‘internalizing psychopathology’ – mental health issues – into adulthood, but only for those who also displayed larger ERN signals at 15.
Neurophysiological markers, such as error-related negativity, may help identify individuals most at risk for developing internalizing mental health problems in adulthood.
The study authors did find, however, that infant BI was not associated with vocational or educational achievements or the outcomes of romantic relationships.
The team conclude that temperament during the first year of life has lasting effects into adulthood – although the study doesn’t account for behavioural changes past the mid-twenties.
Future research will require larger and more diverse samples to establish how much the findings can be generalised.
The study, funded by the National Institutes of Health, has been published in Proceedings of the National Academy of Sciences.