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Causes of Anxiety Disorder

The National Institute of Mental Health supports a sizable and multifaceted research program on panic disorder, its causes, diagnosis, treatment, and prevention. This research involves studies of panic disorder in human subjects and investigations of the biological basis for anxiety and related phenomena in animals. It is part of a massive effort to overcome the major mental disorders, an effort that is taking place during the 1990s, the Decade of the Brain. Here is a description of some of the most important new research on panic disorder and its causes.

Genetics

Panic disorder runs in families. One study has shown that if one twin in a genetically identical pair has panic disorder, it is likely that the other twin will also. Fraternal, or non-identical twin pairs do not show this high degree of "concordance" with respect to panic disorder. Thus, it appears that some genetic factor, in combination with environment, may be responsible for vulnerability to this condition.

Brain and Biochemical Abnormalities

One line of evidence suggests that panic disorder may be associated with increased activity in the hippocampus and locus ceruleus, portions of the brain that monitor external and internal stimuli and control the brain's responses to them. Also, it has been shown that panic disorder patients have increased activity in a portion of the nervous system called the adrenergic system, which regulates such physiological functions as heart rate and body temperature. However, it is not clear whether these increases reflect the anxiety symptoms or whether they cause them.

Another group of studies suggests that people with panic disorder may have abnormalities in their benzodiazepine receptors, brain components that react with anxiety-reducing substances within the brain.

In conducting their research, scientists can use several different techniques to provoke panic attacks in people who have panic disorder. The best known method is intravenous administration of sodium lactate, the same chemical that normally builds up in the muscles during heavy exercise. Other substances that can trigger panic attacks in susceptible people include caffeine (generally 5 or more cups of coffee are required). Hyperventilation and breathing air with a higher-than-usual level of carbon dioxide can also trigger panic attacks in people with panic disorder.

Because these provocations generally do not trigger panic attacks in people who do not have panic disorder, scientists have inferred that individuals who have panic disorder are biologically different in some way from people who do not. However, it is also true that when the people prone to panic attacks are told in advance about the sensations these provocations will cause, they are much less likely to panic. This suggests that there is a strong psychological component, as well as a biological one, to panic disorder.

NIMH-supported investigators are examining specific parts of the brain and central nervous system to learn which ones play a role in panic disorder, and how they may interact to give rise to this condition. Other studies funded by the Institute are under way to determine what happens during "provoked" panic attacks, and to investigate the role of breathing irregularities in anxiety and panic attacks.

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