This kind of therapy has been around for years. Typically a therapist would ask someone to imagine they are experiencing their trauma again. This would happen repeatedly and ideally, with each retelling of what happened, the event would seem gradually less threatening.

Recently Rizzo and other experts have employed virtual reality for this purpose. Patients wear goggles and describe their experiences while a technician stands by with a console changing the scene to fit the patient's description. If the patient recalls hearing a young boy's voice, the technician makes that happen. If the patient experienced the trauma at night or in the daytime, or perhaps was involved in an IED explosion, those circumstances will be created in the virtual world.

"We can begin to pace the exposure in a very evocative fashion," Rizzo said. "This works because some people don't engage in the trauma memory at a sufficient level. They don't engage fully with their imagination to confront difficult memories."

Could a gun range be a form of exposure therapy?

Absolutely not, Rizzo said.

"What happened this weekend with the death of former Navy Seal sniper Chris Kyle at a gun range is exactly the opposite of the evidence-based approach to treating PTSD," termed 'prolonged exposure' or 'virtual reality exposure' therapy, he said. "Chris Kyle, while well trained in his field, had no clinical training in conducting therapeutic exposure."

It is never advisable to put someone with PTSD in an environment where there is likely to be uncontrolled exposure to provocative events -- such as gunfire and visuals of people shooting guns -- because this could stoke a flashback in the PTSD sufferer.

"This would especially not be recommended in a situation where that person had a gun in his/her hand or at least quick access to one. That would truly be a questionable activity and in this case, it was a deadly one," Rizzo wrote in an e-mail forum to journalists who were asking him about the Kyle case.

Conducting exposure therapy requires a well-trained expert clinician in a very controlled therapeutic setting, Rizzo said.

"That is very different than what one could ever reasonably expect in the atmosphere of a shooting range," he said.