Part of Brain That Extinguishes Fears Found

Could lead to new therapy for anxiety disorders, researchers say

WEDNESDAY, Sept. 15, 2004 (HealthDayNews) -- The areas of the brain involved in learning fears have been known, but new research now identifies the areas involved in extinguishing those fears.

"We have been able to identify neural circuits of extinction learning in humans," said study author Elizabeth Phelps, an associate professor of psychology and neural science from New York University. "This is important, because extinction is a model we can use to look at how we get rid of fears we have learned."

Phelps and her colleagues found the area called the amygdala is a key in both learning and unlearning fears. They also found the ventral medial prefrontal cortex is critical for the long-term extinction of fears, according to their report in the Sept. 16 issue of Neuron.

In their experiments, the researchers presented the subjects with either blue or yellow squares. One color was associated with a mild electric shock. Using this method, the subjects acquired a fear of the colored square associated with the shock.

Phelps's team then extinguished the fear response by presenting the colored square associated with the shock, first with a gradually reduced shock and then with no shock at all.

To determine the brain areas involved, the subjects' brains were scanned during the experiment by functional magnetic resonance imaging (fMRI), which uses harmless magnetic fields and radio signals to measure blood flow in targeted areas of the brain. These images reflect the level of brain activity.

"We focused on the amygdala and the ventral medial prefrontal cortex, because research in rats has shown that these are important areas," Phelps explained.

"We found that the amygdala seems to play an important role early on in extinction learning," she noted. Phelps said there are drugs that target the amygdala, which help in the treatment of anxiety disorders.

"The ventral medial prefrontal cortex seems to be more important in retaining this extinction learning," Phelps said. "Both of these regions are important for different parts of the process."

These models for how fears are learned and extinguished are being used to develop treatments for anxiety disorders, Phelps added.

"The more we can understand about these mechanisms and test these mechanisms in humans is going to help us develop effective treatments for these disorders," she said. "It will also help us understand what's going wrong when you have an anxiety disorder."

"More and more research is focused on how we get rid of fears and anxieties," Phelps said. "This is an example of how we can take the kind of things we are doing in rats and show that we are getting the same things in humans. It opens up the possibility for us to translate these animal models to human function and to human anxiety disorders."

"These findings do replicate what people are finding in rats," said Jeffrey B. Rosen, an associate professor of psychology at the University of Delaware. "There is a relationship between the amygdala and the frontal cortex in fear learning and extinction."

Rosen added these findings can be used to help develop treatments for phobias and post-traumatic stress disorder. "It looks like we can learn to extinguish these responses," he said.

More information

The National Mental Health Information Center can tell you about anxiety disorders.

SOURCES: Elizabeth Phelps, Ph.D., associate professor, psychology and neural science, New York University, New York; Jeffrey B. Rosen, Ph.D., associate professor of psychology, University of Delaware, Newark; Sept. 16, 2004, Neuron
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