Post Traumatic Stress Disorderwas called "shell shock" during World War I. The term we use today –  PTSD – is less vivid and more clinical-sounding. But it refers to the same phenomenon: psychological and physical after-effects associated with traumatic experiences.

The disorder has proven difficult to study because its symptoms and their severity vary widely and often present differently in women than they do in men.

Though PTSD is still most popularly associated with veterans of military combat, it is believed to affect civilians who suffer severe abuse or other heightened forms of psychological and physical stress, such as sexual abuse or car accidents.

A new study published in the September 2009Archives of General Psychiatryfocused on soldiers returning from combat in the Iraq war. The study found that PTSD causes chemical changes in the brain that can linger for at least a year. Other studies have found that symptoms persist well beyond one year.

PTSD victims tend to be in a continuous state of heightened alertness. The trauma that precipitates the disorder essentially conditions them to be ever-ready for a life threatening situation to arise at any moment. As a result, they have increased reaction times, which might be characterized as a positive short-term gain. But the continuous release of brain chemicals that accompany this reaction time – and their inability to control when this heightened reactivity will occur – take psychological and biological tolls on PTSD victims over time.

The 2009 study also found that increased alertness was accompanied by a decrease in the ability to learn, retain or even pay attention to information not associated with combat situations. The chemical shift essentially redirects their brains to focus abnormally on immediate survival.

While the 2009 study did not find the soldiers'neurologicalchanges had any connection with depression or alcohol and drug abuse, other studies over the past 25 years  have found addiction and chronic depression to be common in PTSD sufferers.

Other long term side effects of PTSD include an inability to sleep, vivid nightmares and obsessive thoughts surrounding the trauma. Sufferers are also tormented by an "alarm reaction" ( ), becoming jittery or even terrified when loud noises resemble sounds they associate with the trauma. For example, combat veterans often react as if they are being fired at by guns when they are startled by the noise of a car backfiring. Repeated instances of the alarm reaction tax the autonomic nerve system over time – which could result in decreased motor skills and coordination.

Sleep deprivationand the physical strain of prolonged hyper-alertness may eventually lead to a weakening of the body's immune system. Other physical complications like cardiovascular disease could be directly related to the toll PTSD takes on the sufferer's body over an extended period of time.

Emotional disorders like depression seem to be more common in female PTSD sufferers, while men appear more likely to develop addiction problems. Both genders have been found to suffer from panic attacks and violent fits anger. They have difficulty developing or maintaining relationships with other people.Continuous study will give us a clearer picture of what PTSD does to its sufferers in the long term.