NYU Psychology Professor Elizabeth Phelps and her colleagues have developed a technique to block the return of fear memories in humans. Their research may have implications for addressing post-traumatic stress syndrome, fear of crowds, and other anxiety disorders.
“Previous attempts to disrupt fear memories have relied on pharmacological interventions,” said Phelps, a professor in NYU’s Department of Psychology and Center for Neural Science. “Our results suggest such invasive techniques may not be necessary. Using a more natural intervention that captures the adaptive purpose of reconsolidation allows a safe way to prevent the return of fear.”
While researchers have traditionally seen long-term memory as fixed and resistant, it is now becoming clear that memory is, in fact, dynamic and flexible. As a result, the act of remembering makes the memory vulnerable until it is stored again—a process called reconsolidation. During this instability period, new information could be incorporated into the old memory. This was the phase during which the NYU researchers sought to employ a technique to block the return of fear memories.
In a series of experiments, the NYU researchers showed that reactivating fear memories in humans allows them to be updated with non-fearful information. As a result, fear responses no longer return.
To achieve this, the researchers created a fear memory in the laboratory by showing participants a visual object and pairing it with mild electric shocks—a process known as classical fear conditioning. Fear conditioning is successful when subjects show a fear response to the object when it is subsequently presented on its own. In order to measure the fear memory, they examined the skin conductance response to the object, an indication of arousal.
Once this fear memory was formed, participants were reminded of the object a day later. This reactivation of the memory was intended to initiate the reconsolidation process. During this process, information that the same object was now “safe” was provided through extinction training. Presenting this new “safe” information during reconsolidation was designed to incorporate it into the initial fear memory. A day later, the participants were tested again to see whether they continued to demonstrate a fear response when presented with the object.
Extinction training on its own led to the reduction of fear, but fear returned when tested at a later time or when following stress. However, the NYU researchers found that if extinction training was conducted during the reconsolidation window, when the memory was temporarily unstable, fear responses did not return. They also showed that rewriting of the fear memory as safe was specific to the object that was reactivated prior to extinction. Fear memories for other objects returned following extinction, suggesting that the technique is selective rather than having a general effect on memories.
The experiment was conducted over three days: the memory was formed in the first day, rewritten on the second day, and tested for fear on the third day. However, to examine how enduring this effect is, a portion of the participants was tested again about a year later. Even after this period of time, the fear memory did not return in those subjects who had extinction during the reconsolidation window. These results suggest that the old fear memory was changed from its original form and that this change persists over time.