Anxiety gets a lot of bad press. Dwelling on the negative can lead to chronic stress and anxiety disorders and phobias, but evolutionarily speaking, anxiety holds functional value.

In humans, learning to avoid harm is necessary not only for surviving in the face of basic threats (predators or rotten food), but also for avoiding more complex social or economic threats, like enemies or questionable plans.

A team of psychologists at Stanford University have identified a region of the brain, the anterior insula, which plays a key role in predicting harm and also learning to avoid it. In a new study, Gregory Samanez-Larkin and colleagues scanned the brains of healthy adults while they anticipated losing money.

Adults with greater activation of their insula while anticipating a financial loss were better at learning to avoid financial losses in a separate game several months later. Conversely, participants with low levels of insula activation had a harder time learning to avoid losses and lost more money in the game as a result.

For these subjects, higher levels of insula activation helped them to learn to avoid losses months later. However, researchers have found that excessive insula activation might prove problematic. Previous research has shown that people who are chronically fearful and anxious have abnormal patterns of insula activation. So, while people with excessive insula activity are at risk for psychological disorders like anxiety and phobias, higher levels of insula activation in the normal range may allow people to avoid potentially harmful situations.

The findings, which appear in the April issue of Psychological Science, a journal of the Association for Psychological Science, point toward an optimal level of anxiety. While a healthy amount of anxiety grants some survival value, too much may lead to excessive worry and clinical conditions. This may help to explain why anxious traits persist in humanity's genetic endowment, even as environmental threats vary over the ages.