Post-traumatic stress disorder (PTSD) is characterized, among other things, by intrusive memories in the form of unwanted images, nightmares, and flashbacks. These memories are associated with intense distress and involve excessive physiological and psychological responses to fear associated stimuli. Prevalence rates of combat-related PTSD are increasing due to Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) deployments, with the estimated risk for PTSD from service in the Iraq War at 18%, and 11% for Afghanistan.