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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.
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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