An Iraq war veteran with PTSD sits before a self-portrait he painted.

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Thirteen years after he returned home to Las Vegas, Nev., from fighting in Iraq, Adam Kelley, a specialist in the U.S. Army, took his own life. While fighting in the Persian Gulf during the first Iraq war, he watched as one of his friends died. He saw the killing of countless people on both sides. He killed others with the mortar rounds he fired. He was under heavy fire for days at a time. After he returned home, he relived the terrifying events through nightmares and flashbacks. Ultimately, although he was treated with medications, he was unable to shake his demons. Kelley shot himself [source: Rogers].

What Kelley endured for 13 years is what researchers now refer to as post-traumatic stress disorder (PTSD). Previously called soldier's heart, it was first described by Jacob Mendes Da Costa, a doctor during the American Civil War. Marked by chronic tachycardia (high heart rate), and reactivity (increase in heart rate due to a stressor), it looked very much like cardiac disease, but Da Costa recognized the possibility that it was brought on by wartime trauma. PTSD was first noticed on a massive scale during World War I, when it was called shell shock and was described by physician Charles Myers in the medical journal The Lancet in 1916. Interestingly, Myers believed that, at least in part, the symptoms were caused by subtle injury to the brain resulting from the overpressure of exploding artillery rounds. It turned out he was prescient; this is what experts now believe is the cause of mild traumatic brain injury (mTBI). Many symptoms of mTBI overlap with PTSD [source: Myers].

The first diagnosis of the modern view of PTSD came in 1980. Research into this anxiety disorder began intensely after Congress requested a study of how Vietnam veterans were adjusting back to civilian life in 1983. The National Vietnam Veterans' Readjustment Study turned up a wealth of statistics and provided rare, large-scale insight into the nature of PTSD.

But there's still much to learn. For instance, there's no comprehensive data on the number of people with PTSD who, like Adam Kelley, commit suicide. And there's debate over how many soldiers fighting in the second Iraq war are vulnerable to developing the disorder later on. Also, many health care professionals are still exploring the best type of counseling and medication to most effectively treat PTSD.

But the findings from the Vietnam study helped to advance human understanding of the effects of PTSD by leaps and bounds. We now realize, for example, that the part of the brain that stores memories of fearful incidents can be directly related to the development of the disorder. We also now know that some people are more prone to develop PTSD after experiencing a trauma than others. And the duration, intensity and danger of a traumatic experience are known to be directly related to the development of PTSD. Furthermore, the number of exposures is additive, meaning additional exposure to new traumatic situations will compound an existing condition [source: Vasterling et al].

It's also clear to researchers that PTSD can develop in people who have never set foot on a battlefield. The disorder occurs in men, women and children, as a result of a number of traumatic experiences. It's also a question of perception; that is, the traumatized person believes she was in terrible danger, even if someone else might not see it that way.

It's this expanded understanding of PTSD that will eventually allow mental health professionals to properly treat the disorder and also help clinicians to create new drugs and find ways to use existing drugs that not only alleviate the symptoms of the disorder, but also the mental processes behind them. Some drugs that formerly seemed unrelated to PTSD are being used to treat the disorder. The military is even exploring the possibility of developing an "inoculation" against PTSD (more on that later).

But in many ways the disorder is still a mysterious one, and people with PTSF are often misunderstood. In this article, we'll examine the effects it has on the lives of people who have it and the treatments.