 5. Enrolled in cognitive-behavioralexposure-based therapy for PTSD during study period. Supportive therapy and some psychiatric medications if stabilized at least 3 months prior to enrollment are acceptable. Although patients may use medications, no new medications will be started during the study. This includes, but is not restricted to, SSRIs, benzodiazepines, barbiturates, antiepileptic drugs, antidepressants, buspirone, non-benzodiazepine hypnotics, stimulants, or antipsychotics. 