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Sigmund Freud was fascinated with anxiety and recognized early on that there is more than one kind. He identified two major forms of anxiety: one more biological in nature and the other more dependent on psychological factors. Unfortunately, his followers were so obsessed with his ideas about sex drives and unresolved conflicts that studies of the physical basis of anxiety languished.
In recent years, however, researchers have made significant progress in nailing down the underlying science of anxiety. In just the past decade, they have come to appreciate that whatever the factors that trigger anxiety, it grows out of a response that is hardwired in our brains. They have learned, among other things:
--There is a genetic component to anxiety; some people seem to be born worriers.
--Brain scans can reveal differences in the way patients who suffer from anxiety disorders respond to danger signals.
--Due to a shortcut in our brain's information-processing system, we can respond to threats before we become aware of them.
--The root of an anxiety disorder may not be the threat that triggers it but a breakdown in the mechanism that keeps the anxiety response from careering out of control.
Before we delve into the latest research, let's define a few terms. Though we all have our own intuitive sense of what the words stress and fear mean, scientists use these words in very specific ways. For them, stress is an external stimulus that signals danger, often by causing pain. Fear is the short-term response such stresses produce in men, women or lab rats. Anxiety has a lot of the same symptoms as fear, but it's a feeling that lingers long after the stress has lifted and the threat has passed.
In general, science has a hard time pinning down emotions because they are by nature so slippery and subjective. You can't ask a rat if it's anxious or depressed. Even most people are as clueless about why they have certain feelings as they are about how their lungs work. But fear is the one aspect of anxiety that's easy to recognize. Rats freeze in place. Humans break out in a cold sweat. Heartbeats race, and blood pressure rises. That gives scientists something they can control and measure. "You can bring on a sensory stimulus that makes an animal--or human--fearful and study its effects," says Dr. Wayne Drevets of the National Institute of Mental Health (NIMH). "Then you can take the stimulus away and see how the animal calms down."
Indeed, a lot of what researchers have learned about the biology of anxiety comes from scaring rats and then cutting them open. Just as the Russian physiologist Ivan Pavlov showed 100 years ago that you could condition a dog to salivate at the sound of a bell, scientists today have taught rats to fear all kinds of things--from buzzers to lights--by giving them electrical shocks when they hear the buzzer or see the light. The animals quickly learn to fear the stimulus even in the absence of a shock. Then researchers destroy small portions of the rats' brains to see what effect that has on their reactions (an experiment that would be impossible to conduct in humans). By painstakingly matching the damaged areas with changes in behavior, scientists have, bit by bit, created a road map of fear as it travels through the rat's brain.