[The Day They Came to Tell Me My Husband Died]

On another mission months later, I heard a boom and saw a Humvee turn into a ball of fire — one person, engulfed in flames, was running away from the vehicle. Another I.E.D. attack. I fired my M16 rifle toward an insurgent who was hiding in a building and shooting at us. Then I assisted the other medics in treating the casualties. My gloves smelled of soot from cutting the singed uniform pants off a young, dying Iraqi interpreter. “Keep breathing,” I told her. Then I helped load her into a vehicle that would transport her to the medevac helicopter, but by the time it arrived, she was already dead. Another Iraqi interpreter, probably the person I’d seen run from the Humvee in flames, was being treated by my fellow medics. He was evacuated with grave injuries; he, too, later died. When those initial rescue efforts were completed, I helped search the road for pieces of the dead American serviceman whose scorched upper body I saw on the ground next to the destroyed truck.

The images of these traumatic events are seared into my brain. I can conjure them at will. But there remains a sense of control and detachment when I think about them. This is much different from those with PTSD, who try to avoid thinking about their experiences because the memories churn up emotions and a physical response.

On the second day, I slid into the M.R.I. machine; probes were attached to my left hand to measure my pulse and sweat, and a shock device was attached to my right. A drop of sweat trickled down from my armpit despite the coolness in the room, and I waited. Goose bumps formed along my arms. I was shown videos of playful animals. I was nervous, but curious too. The yellow light I saw in the mirror no longer heralded a shock as it had the day before. After a few rounds of seeing multiple colors, I started to realize that I wasn’t receiving any shocks at all. The experiment was trying to convey the lesson that the yellow light was not a danger and no longer merited a fear response.

Some studies suggest that the amygdala, a part of the brain associated with the fear response, is smaller in size but more active in those with PTSD. The medical community is still studying whether this is a genetic difference or a response to traumatic events. The dominant theory about PTSD is that a maladaptive fear response is learned during and after traumatic events, so that even minor triggers can cause people with PTSD to suffer severe surges of anxiety, alarm or fear. Because of conditioning, the brain does not register that it is no longer in a threatening environment. For example, driving by trash on the side of the road in the United States typically does not elicit a fear response. It can for veterans with PTSD who served for months in Iraq or Afghanistan scanning the road for roadside bombs. Their brains cannot differentiate the highways in the United States from those in Baghdad. This can make a simple drive to the store a nerve-racking experience, complete with sweating, flashbacks and heightened sensations.

On the final day of my M.R.I. sessions, I was shown scenes from a Vietnam War movie. The research assistant and the M.R.I. technician remained behind the glass across the room, seated in cushy rolling chairs. The M.R.I. scans tested to see if my fear response could change — if my brain could learn to react less to prompts that had previously come with a sense of physical danger. I imagined being stuck in this tube of doom if I was someone for whom the violent images from the war movie, the sounds of shooting guns and yelling soldiers, did trigger a panic response. Why would someone with PTSD put themselves through this? Wouldn’t it conjure up their anxiety all over again? My anxiety was tinged with excitement; I guessed theirs would be tinged with despair.

In the end, the whole process forced me to re-examine my relationship to trauma. Before the study, I had questioned whether I deserved health and happiness. I naïvely thought having PTSD would validate my military experience. I didn’t know why I was able to suffer and yet still move on. But being part of a control group of people without the diagnosis gave me some relief from that guilt. I started to find purpose in my experiences by giving back as a research-study participant. Perhaps that’s why we all had volunteered: to find some meaning in our military service, whether it had left us traumatized or left us wondering why we were not.