Shy toddlers risk later mental illness

Shy toddlers are likely to grow into shy adults whose emotional inhibitions put them at greater risk of developing more serious mental disturbances, says a 20-year study.

An inhibited temperament - marked by shyness, caution or withdrawal - tends to stay with someone for life and is linked with hyperactivity in a region of the brain known as the "seat of fear".

Scientists analysed the behaviour and brain patterns of 22 young adults whom they had interviewed twice before, once as early teenagers and once as small children.

They were particularly interested in the way the brain's amygdala - an almond-sized structure known to initiate fearful emotions - responded, as measured by a brain scanner, to the sight of strangers, a well-tested measure of shyness.

Carl Schwartz, a psychologist at Massachusetts General Hospital and the Harvard Medical School in Boston, said there was a clear division in the way the amygdala reacted between those who were shy as children and those less inhibited.

"Our findings both support the theory that differences in temperament are related to differences in amygdala function - something earlier technology could not prove - and show that the footprint of temperamental differences observed when people are younger persists and can be measured when they get older," Dr Schwartz said.

The research suggests that there is a strong genetic component to a person's temperament, which predisposes them to either shyness or sociability, caution or boldness, withdrawal or approach.

At the two extremes, inhibited children tend to be timid with new people, objects or situations, but uninhibited children will approach them without apparent fear.

When the subjects were having their brains scanned they were shown photographs of faces, some of familiar people, others of strangers.

Those who were previously categorised as inhibited were more likely to have more active amygdalas when viewing the pictures of strangers, according to a report in the journal Science.

"It's been theorised that the behavioural differences that characterise inhibited and uninhibited children may relate to the amygdala's response to novelty, and our study supports that concept," Dr Schwartz said.

"Now we're suggesting that the same link continues through life. We found that individual differences in temperament are associated with persistent differences in the response of the amygdala after more than 20 years of development and life experience."

One implication of the work is that it could help to diagnose and possibly treat more serious mental disorders at an earlier stage in development. Inhibited children may be more likely to develop social anxiety disorder, which could be a precursor to clinical depression.

"It's only by understanding these developmental risk factors that one can really intervene in the lives of children early, to prevent suffering later in life," Dr Schwartz said.

Scott Rauch, of the Harvard team, said the work suggested that some children were born with a predisposition for an active amygdala that persisted into adulthood.

"Our results suggest that this brain activity may be a marker for the continued influence of temperamental risk factors persisting from infancy."

- INDEPENDENT