The Effects of Very Brief Exposure on PTSD in U.S. Combat Veterans

The prevailing treatment for Post-traumatic Stress Disorder (PTSD) is exposure: the confrontation of traumatic memories, in one form or another. Although exposure therapies are effective for combat related PTSD, confronting traumatic memories is inherently aversive, which may contribute to problems with patient acceptance. For example, trauma-focused PTSD therapies have higher dropout rates than non-trauma-focused therapies, and combat vets who drop out in real-world practice have more avoidance behaviors and greater arousal than those who remain in treatment. Study investigators have developed an alternative form of exposure that has been repeatedly shown to reduce behavioral, physiological, and self-reported fear symptoms in phobic persons without having them directly confront feared situations, and thus without causing them to experience emotional distress. In Very Brief Exposure (VBE), a series of pictures representing a person's fears (e.g., a combat scene with arousing visuals) is presented very briefly (17 ms), followed by a masking stimulus that prevents conscious recognition of each picture. This sequence of picture-mask stimuli is repeated many times in an exposure session.

The goal is to develop a new behavioral treatment for U.S. combat veterans with PTSD, VBE to combat-related stimuli by:

1. Identifying the unique effects of masked exposure to combat-related images (VBE) on the brain activity of U.S. combat veterans with PTSD. Study investigators will conduct a randomized controlled trial of VBE during fMRI scanning by manipulating awareness of exposure to combat-related stimuli, comparing the effects of VBE and (barely) visible exposure to these stimuli on the brain activity of 40 combat veterans with PTSD. Visible exposure to combat images is an active control condition that demonstrates the advantages of implicit exposure (VBE) in engaging extinction circuits and reducing fear responses. These advantages are not merely the consequences of exposure, but of how that exposure is delivered. The study thesis is that exposure is more effective, both in terms of circuit activity and fear responses, when delivered implicitly. Study investigators will manipulate the number of exposure sessions within each treatment group in order to identify the optimal number of sessions.
2. Directly relating the effects of VBE on neural activity to those on behavioral symptoms of PTSD. Subjective fear levels will be measured. In statistical analyses, changes in brain activity induced by VBE will be directly related to its ensuing effects on all of these measures, and the neural mechanisms that mediate the reduction of PTSD symptoms will thereby be inferred.