You are driving at night down a quiet suburban street, listening to Van Morrison's ''Brown Eyed Girl'' on the stereo. As you cross an intersection, your peripheral vision picks up the flash of headlights descending on the right side of the car. In the split second before you hear the sound of metal grinding into metal, your body tenses, blood flows to your extremities, adrenaline surges, and time slows down. At impact you find yourself noticing surreal details—the bright orange jacket of a startled pedestrian, the low-hung branches of a dogwood tree at the side of the road. After a split second that seems like 10 minutes, your car lurches to a halt against the curb.
The physical event of one car colliding with another has run its course, but its emotional impact continues. The adrenaline and other stress hormones released in your body have brought you to a state of almost superhuman alertness; you feel more awake than you've felt in your entire life. You can review the details of the crash as though you were replaying a DVD of the event, all the details immaculately preserved. For weeks, as memory fades, details continue to haunt you. Driving through an intersection causes you to flinch, anticipating another crash; the flash of headlights makes your gut tighten. For months, driving at night seems far more dangerous than driving during the day. Even a year later, the sight of drooping dogwood flowers triggers a sense of dread. Hearing ''Brown Eyed Girl'' brings the whole sequence back to consciousness with astonishing clarity.
Anyone who has been through a traumatic event will recognize this scenario immediately—the sudden physical response of fear and its often debilitating persistence in memory. The feeling of fear, like all emotions, is something that happens to the body and the mind. Few memories are as easily triggered and as hard to shake as those in which we are confronted with an immediate threat. For people who have undergone serious trauma, including war veterans and rape survivors, memories of fear can sometimes play a dominant role in shaping personality, a condition we now call post-traumatic stress disorder.
Unraveling the mystery of how the mind experiences fear—perhaps the most primal and enduring of all the emotions—turns out to be one of the most interesting and instructive quests in the annals of recent neuroscience. We have learned that fear plays tricks with our memory and our perception of reality; we have also learned that the fear systems in the brain have their own perceptual channels and their own dedicated circuitry for storing traumatic memories. As scientists have mapped the path of fear through the brain, they have begun to explore ways to lessen its hold on the psyche, to prevent that car accident from keeping us off the road months later.
