University of Wisconsin-Madison researchers have discovered the part of the brain linked to anxiety in young monkeys, a finding that could help our understanding of the neural basis of temperament in human children as well.

''They were able to link behavioral traits related to anxiety with strong and stable activity of a central circuit of brain area,'' said Alessandro Bartolomucci, a psychobiologist at the University of Parma in Italy, who was not involved in the research.

The central core of the brain's anxiety center was found in the amygdala, a part of the brain that controls emotional reactions, such as the fight or flight response.

Antsy monkeys with high amygdala activity also had greater levels of the stress hormone cortisol in both safe and threatening environments.

''The circuit in the brain is predictive of how anxious and how high levels of stress hormones are in the monkey,'' said University of Wisconsin-Madison psychiatry professor Ned Kalin.

''If you take a young monkey and put it in a situation that is uncertain or a little scary, the animals that have the greatest activity in the amygdala are the ones that appear to be the most anxious.''

Kalin, together with his graduate student Andrew Fox, measured brain activity, cortisol levels and behavioral traits in adolescent rhesus macaques, which have long been used as a model to understand anxious temperament in human children.

The researchers injected a radioactive dye and tracked the monkeys' brain activities in a number of situations ranging from being at home with cage-mates to being alone in a novel environment to being confronted by an unfamiliar person.

''Individuals that have a predisposition (to anxiety) have a brain circuit that is always on; it doesn't turn off like in normal individuals,'' said Kalin, who published his findings this month in the journal Public Library of Science ONE.

These signature anxiety-related traits are analogous to children who hide behind their parents' legs, fail to smile or are otherwise extremely timid in unfamiliar situations.

Many studies have shown that behaviorally inhibited children are significantly more likely to develop social anxiety disorders in later life. These new findings in young monkeys point to the brain mechanisms that predispose children to mental illness.