PTSD is not as palpably physical a wound as a burn or a broken bone, but the disorder leaves a real physiological scar on the human brain. When a person experiences a traumatic event—a rape, a car accident, a tour of duty—the fear-stoking amygdala sends panicked messages to other regions of the brain, including the hippocampus (the brain's HQ for storing long-term memories). The adrenal glands flood the body with fight-or-flight stress hormones, searing fragments of the memory onto the mind with a fire that's hard to extinguish: Past events reignite in the present tense, taking the shape of nightmares and flashbacks.

What's more, anytime the patient stumbles on a trigger—the smell of stale cigarette smoke that she associates with her rapist, a backfiring car that sounds like gunshots in Basra—the amygdala reactivates and stress hormones crank themselves up afresh, reinforcing the memory and creating a vicious cycle. MRI scans of PTSD patients show decreased volume in the hippocampus and lower activity in the prefrontal cortex, both of which modulate the amygdala.

"A strong emotional reaction to extreme stress is normal and adaptive," says John Krystal, MD, chair of the psychiatry department at the Yale School of Medicine and chief of psychiatry at Yale–New Haven Hospital. "In fact, many of the lessons of extreme stress are important—for example, a person who's injured in a car accident might learn to be a more careful driver." But PTSD teaches the brain some skewed and inflexible lessons. "Responding to threats with aggression is highly adaptive in war, but it can have disastrous effects on a marriage," Krystal says. "Or if someone is sexually assaulted, she may learn to mistrust all intimacy and end up depriving herself of emotional support that she needs to cope."

Emily, a 51-year-old horticulturist in San Francisco, showed symptoms of PTSD after she was raped by an acquaintance in 2003. "Most people can draw on a reserve of psychological strength when they need it," she says. "With PTSD, you exhaust all your strength just trying to get to work, pay the bills, feed yourself, and keep up the facade that you're a normal person. So when a little thing comes along like a flat tire or a coworker in a bad mood, all that's left is that fight-or-flight panic response."

For years after the rape, Emily slept terribly, and when she did, she kept having the same nightmare: "A guy—sometimes the guy who raped me—would walk into my home or my workplace and drive a knife into my chest, over and over. I'd wake up sweaty and panicked." She got drunk almost every night. When she was having sex with her boyfriend, she couldn't close her eyes because she'd see her rapist's face. Her temper was short. At an office where she worked, a former coworker brought in her infant one evening. "She was changing the baby's diaper on a table, and I just started screaming at her—I went totally off the wall. That's when my boss took me aside and said, 'You need to get help.'"

The paradoxical power of trauma is that it hides in plain sight; its potency depends in part on the victim's never really looking it in the eye. "PTSD is maintained by avoidance," says Barbara Rothbaum, PhD, director of the Trauma and Anxiety Recovery Program at Emory University. "The memory gets frozen in time, and it's often tangled up with feelings of guilt and responsibility. You have to look at the trauma closely and break down your fear of the memory, so you can start thinking about it differently. But you can't think about it differently if you can't even think about it."


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