In people with anxiety disorders, the brain circuitry that controls the threat response goes awry. At the heart of the circuit is the amygdala, a structure that flags incoming signals as worrisome and communicates with other parts of the brain to put the body on alert for danger. Early life events, especially traumatic ones, can program the circuitry so that it is oversensitive and sends out alarms too frequently and with only minor provocations. Survival mandates a system for perceiving threats and taking quick, automatic action, but those with anxiety see threats where there are none, perhaps because emotional memories color their perceptions.
Occasional anxiety is an expected part of life. You might feel anxious when faced with a problem at work, before taking a test, or before making an important decision. But anxiety disorders involve more than temporary worry or fear. For a person with an anxiety disorder, the anxiety does not go away and can get worse over time. The symptoms can interfere with daily activities such as job performance, school work, and relationships.