April 4, 2001 (Washington) -- Fear can be a powerful influence on behavior, even when we don't think about it. For example, it does not take a genius to figure out that coming face to face with a tiger would not be a good thing. But did you ever wonder why a caged tiger does not trigger the same response?
Thanks to new brain imaging techniques, mechanisms for tracing pathways of nerves in the brain, and instruments to measure the brain's electrical activity, scientists finally are beginning to answer this and other questions regarding human phobias and fears.
Many of the developments have been made in the last decade. Recent advances range from the development of the electroencephalograph, an instrument used to measure the electrical activity of the brain, to computer-assisted imaging techniques that can be used to visualize the structure of a living brain.
Anyone can experience fear. But when fears become persistent and are associated with anxious anticipation or avoidance of triggers that spark the fear -- enough to interfere with your life and disrupt your ability to function -- then it's not just a fear; it's a phobia, and phobias generally require treatment.
By developing a virtual map of the brain's activity when confronted with danger, researchers now hope to someday develop treatments to aid everyone from those who are afraid to leave the house to those who suffer from everyday phobias, such as the fear of heights or even spiders.
"The clinical implications are very simple. If you know the basic circuitry, you know where to look," explains Michael Davis, PhD, a professor of psychiatry and behavioral sciences at Emory University School of Medicine in Atlanta.
One target of the present research is a small part of the brain, located behind the temple, called the amygdala. Since 1939, scientists have suspected that the amygdala may play a large role in how people respond to fear and phobias.
In animals, it has been demonstrated that the amygdala acts much like a "smart" alarm, evaluating the surrounding environment for danger signals and inhibiting or facilitating a fear-related response as warranted. For instance, it has been shown that while the amygdala might trigger a rabbit's heart to beat faster when a predator is at hand, to enable him to run away -- it also could inhibit this natural reaction if the rabbit is caught and needs to play dead.
The new technology is now helping researchers confirm those suspicions and apply animal research findings to the human brain.
At a major conference sponsored by the National Institutes of Health, Davis and other pioneers in the field recently gathered to share their insights.
Significant progress has been made due to human participation, according to the researchers, because unlike animals, humans can describe their emotions, explains Richard Davidson, PhD, a professor of psychology and psychiatry at the University of Wisconsin in Madison.
"What we are learning is that the amygdala is part of a whole network," Davis says. It is now known that while the amygdala appears to play a subtle yet important role in distinguishing signals of danger, its role appears to be associated with the emotional aspects of danger, rather than the thinking part of the response to fear.
"A face is just a face in the visual cortex, but it becomes an angry or happy face when it reaches the amygdala," explains David Amaral, PhD, a research director at the University of California Medical Center in Davis, who spoke at the conference.
Understanding the different components of fear responses -- both emotional and based on thought -- and how they interact is important for developing treatments, Davis tells WebMD. But in terms of treatment, a major target is getting rid of disruptive memories that can recur and spark fears at any time, he says.
To that end, Davis and his colleagues are now working on the development of compounds to inhibit the reactions triggered by the amygdala. The research is still in its infancy, but someday, they hope these compounds can be used as treatments for a number of fear-related conditions, including posttraumatic stress disorder (PTSD).
PTSD is the severe emotional reaction to a traumatic event, such as a flood, fire, war, assault, domestic abuse, or rape. People with PTSD often re-experience the event in the form of recurring nightmares or flashbacks. These events usually follow the exposure to a symbolic trigger, such as a loud noise or an anniversary of the traumatic event.
At present, PSTD is treated using common behavioral techniques. These techniques are based upon either gradual or frequent exposure of the patient to symbolic triggers of their emotional trauma. The goal of this therapy is to help them gain a sense of mastery over the experience.
The goal of the new treatments would be to suppress the fear-related response caused by the amygdala, when it occurs at inopportune moments, Davis says. In essence, he tells WebMD, the goal of the new treatments would be to reinforce the behavioral therapy by helping the amygdala to master the experience as well.
One such compound might be an inhibitor of glutamate, a chemical that transfers messages between nerves and that has been shown to influence various brain functions, Davis says. By inhibiting this chemical in certain parts of the brain, scientists may be able to assist the amygdala to suppress the fear-related response when exposed to symbolic triggers, he says.
According to Davis, there is a desperate need for these types of treatments. Despite the development of newer agents such as Prozac, which has antidepressant and antianxiety properties, the actual treatment of people's fears and phobias has remained largely difficult because these disruptive memories easily can be re-triggered, he says.
But because scientists know very little about these messenger chemicals in general, Davis says the development of treatments may take some time. Besides finding the right chemicals to target, the drugs will also need years of testing to ensure that they are safe and effective.
Still, the present research offers a lot of hope because it at least pinpoints where the fear response may have its origin.