Dec. 8, 2009 -- Scientists at New York University report they have developed a drug-free, noninvasive way to temporarily block the return of fearful memories in people.
The technique, the researchers contend, could eventually change the way scientists view how the brain’s memory storage process works and perhaps even lead to new ways to treat anxiety disorders, including posttraumatic stress disorder.
Researcher Daniela Schiller, PhD, and colleagues at NYU say in a new study published in the journal Nature that they’ve been able to reshape memories. The process involves resurrecting unpleasant memories and creating a window of opportunity for reshaping the fears, a period called “reconsolidation.”
“Reconsolidation is a natural process that is likely occurring all the time,” Elizabeth Phelps, PhD, a professor of psychology at NYU, tells WebMD in an email. “Our studies suggest that simply retrieving a memory is enough to trigger the reconsolidation (i.e. re-storage) process. The trick is knowing enough about exactly how this process occurs to take advantage of it to restore fear memories as safe.”
Blocking Fear Memories
The researchers “trained” volunteers to be fearful of a visual stimulus, in this case colored squares, by pairing the images with mild electric shocks in a process called classical fear conditioning. Then they measured moisture on the skin of the volunteers, an indication of fear arousal.
After the fear memory was formed, some of the 65 participants were re-exposed to the image that produced the electric shock. This was followed by “extinction training,” in which they were exposed to colored squares but not shocked.
“The term extinction is generally used to describe new learning that the previously feared event is now safe,” Phelps tells WebMD.
The fear response disappeared only in people who went through extinction training. Those people who received extinction training after a six-hour window remained afraid of the squares, as did those in a control group.
Timing Is Critical
A year later in a follow-up experiment, 19 of the original participants received four shocks followed by presentations of the colored squares. This was meant to reinstate fears.
Those who had undergone extinction training within a six-hour window were largely spared significant effects, the authors say.
People whose training had been delayed six hours or who hadn’t experienced a fear memory reactivation prior to extinction training experienced the fear response again.
“Our research suggests that during the lifetime of a memory there are windows of opportunity where it becomes susceptible to be permanently changed,” Schiller says in a news release. “By understanding the dynamics of memory we might, in the long run, open new avenues for treatment of disorders that involve abnormal emotional memories.”
“Timing may have a more important role in the control of fear than previously appreciated,” Phelps says in a news release. “Our memory reflects our last retrieval of it rather than an exact account of the original event.”
New Treatment for Fear Memories?
The authors say the experiments represent the first time a fear memory has been blocked in humans with a behavioral manipulation.
Thomas R. Insel, MD, director of the National Institute of Mental Health, says the study holds “promise for being translated into improved therapies for the treatment of anxiety disorders, such as posttraumatic stress disorder.”
Other researchers included Joseph E. LeDoux, PhD, of the University of Texas. LeDoux and a team of researchers conducted similar experiments on rats earlier this year, producing similar results.