So once a week, Frey has agreed to meet with Dr. James Spira at the Naval Medical Center in San Diego for therapy sessions. But instead of just talking about his experiences in Iraq, Frey puts on special goggles to relive them inside of a realistic videogame-like simulation that re-creates the sights, sounds --- and soon --- the smells of the battlefield. It's called exposure therapy.

Inside the virtual world, Frey sees a generic Middle Eastern desert city that could easily double for Baghdad. It is quiet at first. Sensors attached to his fingers and body display heart rate, breathing and other information on a monitor for Spira to see how his patient is responding.

When he's sure Frey is doing all right, Spira begins clicking his mouse to gradually add ambient noises like distant gunshots and jets flying overhead. Frey's breathing becomes shallow. His heart rate increases. Next, he begins to hear accented voices shouting at him, saying things like "Go home cowboy!" The sounds of explosions and machine guns get louder as a Blackhawk helicopter swoops in for a landing in the middle of the street.

"This isn't real," Spira reassures Frey. "Just reminders from the past. You can let those thoughts be further away, more distant. They will still come, but you don't have to pay attention to them. You can say to yourself, 'these are just memories.' "

The virtual reality world, Spira said, "triggers those thoughts, those feelings, those earlier reactions they had. What we're trying to do now is train them to have different reactions to those same stimulus and reminders."