In a new study, researchers have manipulated the brain’s own memory process to extinguish fear. In a series of experiments using only colored squares and skin shocks, a team from New York University and the University of Texas induced a fearful memory and then erased it. Participants remained free of the specific fear memory for at least a year.
“It’s the first evidence that emotional memories in humans can be affected without drugs. That’s why it’s so exciting,” says Daniela Schiller, Ph.D., of New York University’s Center for Neural Science and Psychology Department, lead author of the study that appeared online Dec. 9, 2009 in the journal Nature and was funded by the James S. McDonnell Foundation and National Institute of Mental Health.
The findings are based on the idea that when memories are recalled, they are vulnerable to change. The researchers were inspired by their previous successful experiments on rats.
Schiller explains that new memories are formed through “consolidation,” which involves complex changes in connectivity between brain cells. Only after that consolidation process is complete do memories become fixed. But retrieving memories prompts another round of consolidation, called reconsolidation, at which point memories become unstable and receptive to interference or even updating.
The researchers suggest that such a window of vulnerability could be an evolutionary adaptation, allowing newly available information to be incorporated into an old memory.
“It shows that in the lifetime of a memory, there are windows of opportunity to change it,” Schiller says.
In the experiments, 65 participants in three groups were conditioned with intermittent wrist shocks to fear a colored square. (Fear was measured by skin conductance). A day later, participants underwent extinction training in which the square was repeatedly presented without shocks.
But prior to the extinction training, groups one and two had been prompted to recall the painful memory (fear reactivation) by a single presentation of the colored square. The first group was prompted 10 minutes before extinction training; the second group, six hours before. The third group underwent extinction training without fear reactivation.
Another day later, each group again confronted the colored square. Only the participants who underwent extinction training shortly after fear reactivation were relieved of the fear response. The other two groups remained afraid of the colored square.
Even after a year, the participants who had undergone extinction training within the presumed reconsolidation window (the first group) were spared the effects of a fear-reinstatement regimen conducted with the colored square and shocks.
The results indicate that a fear response can be updated with non-fearful information introduced during the reconsolidation window.
The findings open windows of opportunity for devising new therapies for treating anxiety disorders such as phobias, compulsions and posttraumatic stress, but research has a long way to go to both define the reconsolidation window and to extend the simple laboratory model to the real world. Among the next steps is the examination of more complex, ingrained memories consisting of combinations of sights, smells and sounds.
“The idea is to gradually extend the lab model to real life fear memories, which are complex, old and intense,” Schiller says. “In the lab, we want to mimic life better, and we want to test patients with these disorders to see if these techniques can be applied in the clinic as a form of therapy.”
She adds, “Unlike the movie ‘Eternal Sunshine of the Spotless Mind,’ we don’t change the content of memory, just the emotional response to it. That’s what we think is happening.”