Inclusion Criteria:  The willingness and ability to read, understand and sign an informed consent form. Age 20-60 years. A history of more than 2 years of combat service, and of at least one potentially life-threatening combat experience. One year or more after the last combat experience.  Exclusion Criteria:  Inability to attend scheduled clinic visits or comply with the study protocol A history of traumatic brain injury or any other known brain pathology. Substance use, except for prescribed cannabis, if it can be withheld for at least 24 hours prior to the study evaluation. A current psychiatric disorder other than PTSD. The inability to perform an awake brain MRI.