This study will develop a new clinical tool for assessing post-traumatic stress disorder (PTSD), which could enable researchers to better treat war veterans suffering from this disabling anxiety disorder. An objective laboratory test, which measures a person's ability to control fear, is currently being used for the first time with Vietnam and Iraq War veterans at the Atlanta VA Medical Center. PTSD, which affects an estimated 20 percent of veterans, is a dysfunction of the brain's fear control mechanisms resulting from a traumatic experience, such as combat. One of the central features of the disorder is the inability of the brain to distinguish between dangerous and safe situations. The ability to inhibit fear can be tested in a simple laboratory experiment that uses the startle response as a way to measure fear. When people hear a loud sound they startle and blink their eyes. The eyeblink can be measured with small wires placed under the eye that detect contraction of the eye muscles and send a signal to a computer. When people are afraid, they startle more. For example, people who have been exposed to pairings of a signal (e.g., a colored light) with an aversive event (e.g., a blast of pressurized air to the throat) startle more, and blink harder, in the presence of that signal than in its absence. This is called "fear-potentiated startle."

After people have learned to be afraid of a particular light, we present that light without the aversive stimulus many times, until the person now learns that the colored light is no longer associated with the airblast. In this way people can learn not to be afraid. This type of experiment is called "extinction learning" and is the basis of many psychological treatments for fear-related disorders, such as phobias and PTSD. A person's ability to learn that something is safe may make them less likely to develop a disorder in the first place, or may make them more likely to recover once they have the disorder. The proposed study will use these tests to see whether this ability is linked to the development of PTSD in combat soldiers returning from Iraq and Afghanistan. The study will also look at blood samples to see whether there are some genes that make people more vulnerable to PTSD by making them less able to suppress their fearful responses.

This test can provide a more objective way of measuring fear control mechanisms that work in healthy people and do not work in PTSD patients. In fact, if this finding holds up in larger studies, it may provide one of the first biomarkers for PSTD, namely an objective physiological measure of fear control dysregulation in this debilitating psychiatric disorder. It may also become a valuable clinical tool to assess and compare the effectiveness of different treatments in different populations of PTSD patients, such as civilian and combat-related PTSD.