Neurobiological Correlates of Post Traumatic Stress Disorder (PTSD) During Rapid Eye Movement (REM) Sleep

General Inclusion Criteria: * Male OIF/OEF returnees between the ages of 18 and 45 years old * Combat Exposure Scale score \> 17 * Not taking medications known to affect sleep or wake function for at least 2 weeks (6 weeks for fluoxetine). * No history of trauma before age 18 Specific Inclusion Criteria for Subjects with PTSD: * Meet diagnostic criteria for current PTSD according to the CAPS-1 * CAPS-1 score is less than 80 Specific Inclusion Criteria for Subjects without PTSD: * Total CAPS-1 scores \< 17 * Does not meet criteria for PTSD Exclusion Criteria: * Trauma occurred less than 3 months prior to study entry * CES score \< 17 * Taking medications known to affect sleep and / or brain glucose metabolism * Current diagnosis of depression as determined by the SCID or BDI score \> 13 * History of psychotic or bipolar disorder * Current history (within 3 months) of substance or alcohol abuse as determined by the SCID * Positive alcohol blood test at screening or during the PET protocol * Significant or unstable acute or chronic medical conditions * Other current sleep disorders, such as insufficient sleep syndrome, delayed sleep phase syndrome, narcolepsy, restless legs syndrome, periodic leg movement disorder, obstructive sleep apnea, and current night shift work, suspected during the structured interview. Individuals who are found to have a apnea-hypopnea index (AHI) \> 10 or an index of periodic leg movements with arousal \> 15 will be excluded. * Presence of implanted devices such as cardiac pacemaker, aneurysm clip, ear implant, shrapnel, neurostimulators or other metal devices * Fear of closed spaces * Previous radiation. Due to the risk of radiation exposure, we will exclude subjects who have had PET scans or other radiotracer exposure in the previous year. * History of open head injury.