In Brief

A compound called D-cycloserine in combination with exposure-based therapy may allow people to more easily break the association between a situation and fear, said Michael Davis, PhD, at a plenary session at APA's 2006 Annual Convention.

Davis, recipient of the 2006 Distinguished Scientific Contribution award and a psychology professor at Emory University, said the discovery stemmed from a career spent investigating the neural basis of fear and anxiety, based on laboratory work with rats. He said he and his colleagues worked from findings made by other researchers who showed that blockading the N-methyl-D-aspartate (NMDA) receptor the amygdala thwarts the process of extinction.

Through extinction, conditioned fear can be suppressed by repeated exposure to a feared stimulus without an aversive event. For someone with an inordinate fear of heights, exposure-based psychotherapy would involve repeated exposure to high places.

When nothing bad happens, the person learns to not be unreasonably afraid.

A compound called D-cycloserine, a commercially available antibiotic used to treat tuberculosis, has been shown to bind to the NMDA receptor and boost its activity in the amygdala. By making the receptor work better, it held the promise that it could strengthen the process of extinction.

One series of experiments started with rats that learned to associate a light and a tone with a shock. After the training period, the experimenters gave some of the rats a dose of D-cycloserine, then exposed them to a light and a tone but no shock. These animals were quicker at extinguishing the startle reflex, than a control group, Davis found.

Those results led Davis and his fellow researchers to wonder if the compound could help people deal with fear and anxiety disorders, Davis said. In one recent study, people who were afraid of heights were given either a dose of D-cycloserine or a placebo a few hours before two therapy sessions.

In the sessions, each participant wore a virtual reality headset replicating the experience of riding a glass-enclosed elevator to the upper floors of a high-rise hotel with an enclosed atrium. The subjects were then asked to "walk" out onto a beam suspended in mid-air, starting at the fifth floor and gradually ascending.

As measured by subjective descriptions of how they were feeling while experiencing the beam walk, both groups reported the same amount of fear during the initial sessions, Davis said.

One week later, the participants went through the elevator experience again. At that time, those who took the D-cycloserine experienced less fear, as measured by readings of galvanic skin response and self report, he said.

In that study, the progress that usually takes people suffering from phobias eight sessions of extinction-based psychotherapy to achieve was reached in two, Davis said.

Researchers also found that three months later, people in the D-cycloserine group reported more willingness to voluntarily put themselves in situations where they used to experience fear, such as driving over a high bridge.

Davis and his fellow researchers presented their findings in Current Directions in Psychological Science (Vol. 14, No. 4, pages 214-219).

"The D-cycloserine group had more real-world exposure to heights at the three month follow-up. Once they get over the hump, they keep exposing themselves to situations, and they keep re-extinguishing themselves," Davis said.

More research is needed to learn if the D-cycloserine approach can be useful for helping people who suffer from panic attacks, post-traumatic stress disorder and obsessive-compulsive disorders, Davis said.

--C. Munsey