(HealthDay is the new name for HealthScoutNews.)
THURSDAY, June 19, 2003 (HealthDayNews) -- Kids who were characterized as "inhibited" when they were toddlers have marked differences in how the amygdala region of their brain functions when they are older, new research suggests.
"Inhibited" and "uninhibited" are temperament types that refer to how well individuals respond to new things. Inhibited children tend to be timid when confronted with new people, objects and situations, while uninhibited children tend to embrace them. The amygdala is a part of the brain region governing emotions and behavior.
Some previous studies have suggested that inhibited children may be more likely to end up with social anxiety disorder, which affects about 5.3 million American adults, according to the National Institute of Mental Health. People who have the disorder tend to suffer from acute anxiety and self-consciousness, to the point that they often avoid various social situations.
"In adolescence, you could think of this as a paralyzing, severe form of shyness," says Dr. Carl Schwartz, lead author of a new study that appears in the June 20 issue of Science. "These are adolescents who may not even go to school. They don't like to raise their hands in class, don't date. They may not have friends because they are so avoidant of situations that involve reactions with unfamiliar people or situations."
In adults, the disorder can be treated with psychotherapy or medication. It's not clear how the disorder can be best treated in children, say the study authors.
It's also not clear how temperament differences apply in adults, although some researchers have speculated that inhibited children may be more likely to develop social anxiety disorder.
One way to answer this question would be to observe actual brain function, since researchers have hypothesized that the amygdala of uninhibited people would react differently than that of inhibited people. The technology to measure this, functional MRIs or fMRI, however, has not been available until recently.
In the new study, Schwartz and his colleagues used this technology to look at brain function in 22 young adults who had participated in earlier research as children. Thirteen of the participants had been characterized as inhibited when they were children. Nine had been categorized as uninhibited.
About nine years after that, when the participants were in their early 20s, the researchers used fMRI scans to look at regions of their brains.
Functional MRI images were taken while the study subjects looked at pictures of six faces, each of which was presented several times. Later, the participants looked at a larger number of faces, some of which were entirely new and some of which were repeats from the first test, also while being imaged.
Participants who'd been "inhibited" children showed a relatively high level of activity in the amygdala, compared to their peers who had been classified as uninhibited. In fact, two of the inhibited children developed social anxiety disorder as adults, while none in the uninhibited group did.
"The conservative interpretation of this is very suggestive of the hypothesis that the difference between these children early in life reflects a difference in reactivity in the amygdala," says Schwartz, director of the developmental psychopathology lab at Massachusetts General Hospital in Boston and an assistant professor of psychiatry at Harvard Medical School. "The Science paper doesn't prove that point [but] it's very strong evidence that that might be the case."
"Through neuroimaging data, we found a footprint of the early temperamental differences. We found that people who were classified as inhibited when they were toddlers later showed differences in the amygdala," Schwartz explains.
"The brain circuitry is still reacting differently," he adds. "It is startling that inborn individual differences in infants' propensity to respond to novelty are associated with persistent differences in the responsivity of the amygdala after more than 20 years of development. This inborn high reactivity in the amygdala appears to be a very potent risk factor for developing a particular kind of anxiety disorder."
The findings may help to start sorting out the nature-versus-nurture debate. About one-third of "inhibited" children end up with social anxiety disorder, versus only 9 percent of "uninhibited" ones.
"What that told us is that the thing called temperament, which isn't a pathology but is part of the basic flavor of human beings, is a risk factor for developing this kind of problem," Schwartz says. "But it's not deterministic or preordained. Over two-thirds didn't develop the problem."
More information
For more on social anxiety disorder, visit the National Institute of Mental Health or the Anxiety Disorders Association of America.
