With each description of scenery or action or sound, the therapist points, clicks and recreates. Participants in the program are encouraged to remember smells, which researchers believe are a particularly strong trigger for reliving experiences. The computer software is connected to a scent machine with an air compressor and fan that puffs out whiffs of 13 scents right near the participant’s nose. Working with military researchers, the specific odors, including cordite, charred hair and gunpowder, all developed by EnviroScent, an Atlanta-based company , use synthetic aromas and essential oils mixed with a gel substrate, said Emorie Sherwood, EnviroScent’s Product Development Manager.

“The sense of smell drives many behaviors because of the way in which the brain is structured. Other senses pass through filters, are separated and processed and then re-integrated into the brain. But with olfactory stimulants, it doesn’t pass through the filtering system,’’ said Ronald Hoover, a U.S. Army’s research portfolio manager. “What we have found is that smell has a more direct connection to the memory, and it’s very salient and tends to be more resilient to the passage of time, which is why you can have childhood memories that are based on a scent.’’

The idea is to tell, retell and relive the most horrific traumas over and over until the memory loses its emotional punch, a process known in psychological circles as exposure therapy and habituation. During treatment, the participant’s heart rate often increases, palms sweat, anxiety surges. At any point, though, they can stop.

“We don’t want the participant to lose the memory. Rather, we want them to be able to take the highly emotional content and process it out of the memory so it’s not so powerful,” said Hoover, a licensed psychologist. “PTSD can be such a debilitating condition. When soldiers return with problems, we take the responsibility to address those with the utmost seriousness.’’

Active-duty service members with PTSD are often re-deployed before they recover, said Hoover. The study also explores whether compressed treatment daily over three weeks is as effective as once a week for 17 weeks. At UCF, the first participants who went through the longer program reported their nightmares decreased from every night to once a month. Earlier this year, the U.S. Army added $1.5 million to develop the three-week intensive program, particularly for active-duty service members. “We have soldiers rotate back out on deployment before they get to finish the therapy, so we are hoping to find treatments that are successful in shorter periods which will heighten our completion rate,’’ Hoover said.

Virtual reality as therapy is not new, just improved. In 1997, researchers introduced Virtual Vietnam. The computer system placed veterans — suffering from what was then called battle fatigue or shell shock — in a jungle or aboard a helicopter hovering over a river.

The new, technologically superior, programs were created by Albert Rizzo, a clinical psychologist at the University of Southern California who began looking at ways to help soldiers almost immediately after the war in Iraq started in 2003. He had already been using virtual reality to treat patients with attention deficit disorders. Then he discovered Full Spectrum Warrior, a game used as a training tool by the Department of Defense and wondered if the same technique could be used in therapy. “We use gaming software to create realistic combat environments. We are bringing the war home so we can treat our wounded service members,’’ he said. “They have gone through and seen horrible things so it’s not easy for them to revisit. It’s hard medicine for a hard problem.’’

Rizzo said the system can be particularly attractive — and without the stigma of traditional treatments — for younger soldiers.

“You have a generation of soldiers, Marines and service members who grew up in a digital world, who have played thousands of hours of computer games,’’ he said. “That is the group you may be able to appeal to and get them to come in and get treatment

Army Sgt. 1st Class Kevin Todd, in the service more than two decades, brought back the horror of war after returning from Kuwait in 2004. He lived with the anxiety, the depression, the nightmares — the relentless loop of killing people or being killed — for seven years before asking for help. Last June, he started the Trauma Management Therapy weekly program — the longer version of the treatment — using Virtual Iraq as part of his recovery.

“The first thing you have to do is admit you have a problem and then be willing to express it, and be willing to talk about what actually happened to you,’’ said Todd, 47, who is in the process of being medically discharged. “I used to have nightmares everyday. I didn’t want to go to sleep. Now I have them a couple times a week. I am making progress.’’