Studies in animals and humans have focused on pinpointing the specific brain areas and circuits involved in anxiety and fear, which underlie anxiety disorders. Fear, an emotion that evolved to deal with danger, causes an automatic, rapid protective response that occurs without the need for conscious thought. It has been found that the body's fear response is coordinated by a small structure deep inside the brain, called the amygdala.
Neuroscientists have shown that when confronted with danger, the body's senses launch two sets of signals to different parts of the brain. One set of signals, which takes a more roundabout route, relays information to the cerebral cortex, the cognitive part of the brain that explains in detail the threatening object or situation such as a big black car heading for you as you cross the street. The other set of signals shoots straight to the amygdala, which sets the fear response in motion, readying the body for quick action before the cognitive part of the brain comprehends just what is wrong. The heart starts to pound and diverts blood from the digestive system to the muscles for quick action. Stress hormones and glucose flood the blood stream to provide the energy to fight or flee. The immune system and the pain response are suppressed to prevent swelling and discomfort, which could interfere with a quick escape. And, as a preventive measure for similar confrontations in the future, the learned fear response is etched on the amygdala. |
Fear Response Turn into an Anxiety
Disorder |
One or more fearful experiences can prime a person to respond excessively to situations where most people would experience no fear—such as in the supermarket—or only moderate
nervousness—such as giving a speech. In anxiety disorders, the deeply etched memory can result in
hyper vigilance, making it hard to focus on other things, and leading to feelings of anxiety in many situations. In people who have survived overwhelming trauma and developed PTSD, for example, even mild reminders of the trauma may initiate the fear response. People with specific or social phobia often completely avoid their feared situation. In panic disorder the chronic worry about having another attack may lead to stress-related conditions such as heart problems and irritable bowel syndrome. In people with generalized anxiety disorder, the chronic anxiety may prevent them from focusing on even the simplest tasks. The amygdala, although relatively small, is a very complicated structure, and recent research with animals suggests that different anxiety disorders may be associated with activation in different parts of the amygdala.
Some Cases of OCD Linked to Earlier Infection
NIMH studies of obsessive-compulsive disorder in young people have shown that the experience of having a streptococcal bacterial infection may lead to the development of crippling obsessions and compulsions. It appears that a genetic vulnerability, coupled with rheumatic fever, is associated with some cases of OCD. Preliminary evidence indicates that special treatment for the infection improves or cures the OCD.
Research Program
In addition to studying anxiety disorders, NIMH supports and conducts a broad based, multidisciplinary program of scientific inquiry aimed at improving the diagnosis, prevention, and treatment of other mental disorders. These conditions include bipolar disorder, clinical depression, and schizophrenia. Increasingly, the public as well as health care professionals are recognizing these disorders as real and treatable medical illnesses of the brain. Still, more research is needed to examine in greater depth the relationships among genetic, behavioral, developmental, social and other factors to find the causes of these illnesses. NIMH is meeting this need through a series of research initiatives:
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The
amygdala findings may have important implications for treating
people who suffer from anxiety disorders. If, as studies
suggest, the memories stored in the amygdala are relatively
indelible, one aim of research is to develop therapies for
anxiety disorders that increase cognitive control over the
amygdala so that the "act now, think later" response can be
interrupted.
The
Role of Cognitive Factors
Cognitive factors play a significant role in the onset of anxiety disorders. People at risk for these disorders tend to be overly responsive to potentially threatening stimuli. Studies are underway to look at how people with anxiety disorders process information. The goal is to see which cognitive capabilities are affected by anxiety and which are free to handle other information. Data collected from the studies should help researchers determine more about the brain pathology associated with anxiety disorders.
Anxiety Research and Genetics
Research evidence points to genetics as a factor in the origin of anxiety disorders. Scientists have recently discovered a gene that influences fearfulness in mice. And NIMH-supported studies of twins have found that genes play a role in panic disorder and social phobia. Although genes help determine whether someone will develop an anxiety disorder, heredity alone can't explain what goes awry. Experience also plays a part. In PTSD, for example, the trauma is the experience that triggers the anxiety disorder; genetic factors may help explain why only certain individuals exposed to similar traumatic events develop full-blown PTSD. Researchers are honing in on the degree of influence that genetics and experience exert in each of the anxiety disorders—information they hope will yield clues to prevention and treatment.
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Clinical Trials of New Treatments
Anxiety disorder treatment studies have been designed so that
pharmacological and cognitive or behavioral therapies can be
tested head-to-head. In one clinical trial, two separate centers
are examining how well drug and behavioral therapies work
separately and together in the treatment of OCD. Data collected
from this study should help scientists determine if one of the
treatments works better than the other in decreasing obsessions
and compulsions. In addition, the direct comparison of the
combined treatment with the medication will provide much needed
information on whether the high relapse rate associated with
stopping the drug can be reduced. The comparison should also
help determine if the medication can enhance compliance with the
behavioral treatment.
Many of the current medications for anxiety disorders affect the neurotransmitter serotonin. New treatment approaches are examining drugs that affect other neurotransmitters and brain chemicals such as GABA, gamma-aminobutyric acid, and Substance P. A new research tool, magnetic resonance spectroscopy will help scientists measure brain levels of GABA and other substances.
Researchers are also looking at combinations of medications that may have a
synergistic effect—in panic disorder, for example, studies are underway to
determine if an antidepressant medication that affects serotonin works
better when used with the new anti-anxiety drug buspirone.
Early Life Stress May Play a Role
In animals, NIMH-funded researchers are studying how stress, especially when it occurs in early life, affects how adverse events are handled later in life. Rat pups who are subjected to the stress of being separated from their mothers for several minutes early in life have, months later, a much greater startle reaction to a stressful event than pups who were never separated. This line of research may help scientists learn how genes and experience affect who is vulnerable and who is resistant to anxiety disorders.
Anxiety Disorders and Hormones
Another area of research has led to the discovery that anxiety disorders are associated with abnormal levels of certain hormones. People with PTSD, for example, tend to be low on the stress hormone cortisol, but have an overabundance of epinephrine and norepinephrine, which could be why they continue to feel anxious after the trauma. In addition, they tend to have higher-than-usual levels of corticotropin releasing factor (CRF), which switches on the stress response and may explain why people with PTSD startle so easily. Scientists are researching ways to correct hormonal imbalances and bring symptoms under control.
The Importance of Imaging Tools
Scientists may be closer than ever before to creating therapies that are specifically targeted. NIMH studies use imaging tools to allow researchers to peer into the living brain and watch the amygdala, the cortex, and other areas of the brain at work. They can identify abnormal activity when a person has an anxiety disorder and determine if medication or cognitive and behavioral therapies help to correct it.
Recent studies of the brain using magnetic resonance imaging
showed that people with OCD had significantly less white matter
than did control subjects, suggesting a widely distributed brain
abnormality in OCD.
Human Genetics Initiative
This project has compiled the world's largest registry of
families affected by schizophrenia, bipolar disorder, and
Alzheimer's disease. Scientists are able to examine the genetic
material of these family members with the aim of pinpointing
genes involved in the diseases.
Prevention Research Initiative
Prevention efforts seek to understand the development and expression of mental illness throughout life so that appropriate interventions can be found and applied at multiple points during the course of illness. Recent advances in biomedical, behavioral, and cognitive sciences have led NIMH to formulate a new plan that marries these sciences to prevention efforts.
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