Published online by Cambridge University Press: 27 July 2009
Most people who experience trauma do not develop posttraumatic stress disorder (PTSD). While 75% of adults have had a traumatic experience fulfilling current DSM–IV criteria as potential factors in the development of PTSD, only 12% actually developed PTSD (Breslau & Kessler, 2001). This suggests that the majority of persons are highly resilient in the face of trauma (Charney, 2004). What are the neural mechanisms that allow a person to recover from trauma without enduring effects? Recent work has focused on extinction of classically conditioned fear as a useful animal model of recovery after trauma. In cued fear conditioning, a tone is paired with a mild footshock. After several such pairings, rats learn that the tone predicts the shock and exhibit a range of species-specific fear responses, including freezing and potentiated startle responses (see Rau & Fanselow, this volume). In extinction, the conditioned tone is repeatedly presented without the shock, causing rats to learn that the tone is no longer dangerous. Understanding the neural mechanisms of extinction learning could lead to new treatments for PTSD, given that extinction underlies exposure-based therapies used to treat PTSD (Foa, 2000; Rothbaum & Schwartz, 2002).
EXTINCTION OF FEAR IS NEW LEARNING
While it may be tempting to think that extinction of conditioned fear simply erases the original tone–shock association, substantial behavioral evidence suggests that this is not the case.