A drug-free treatment sometimes used to treat Post-Traumatic Stress Disorder (PTSD) is being tweaked by researchers to permanently erase the association of pain with a memory. Known as extinction therapy, a patient is exposed to threatening cues such as gunshots in a safe environment, in the hopes of overriding the fearful associations. Unfortunately fearful memories often reappear in time.Marie Monfils, a neuroscientist at the University of Texas in Austin, noticed that the process of jogging a memory, such as with an emotional or sensory stimulus, can make it malleable for a few hours afterwards. This feature of memory is called reconsolidation. Monfils wondered if the fearful memories that were altered in extinction therapy could be permanently erased through repetition of the treatment during the malleable period.
Her team taught rats to associate receiving an electric shock with a particular sound. When they played the sound, the rats tensed in anticipation of pain. When they used conventional extinction therapy and repeated the sound over and over, gradually the rats showed less fear. However a month later the rats showed the same fears as before, as strong as it was originally.
The team then attempted to use the malleability of memory in the reconsolidation window to erase the memory permanently. After again teaching rats to associate an electric shock with the sound, they played it without the shock and the rats showed fear. This time they waited an hour to be sure that the reconsolidation window had begun, and then repeated the sound constantly. After their fear lessened, and eventually disappeared, the rats never showed fear of the sound again.
A theory proposed by Monfils is that extinction therapy creates a new pain-free memory of the stimulus (The tone or the square) along with the original painful memory, and over time the original may be remembered. Waiting for the reconsolidation window however seems to overwrite the original memory, completely replacing it and permanently removing the fear response.
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