Wednesday, December 30, 2009
A fear conditioning study finds a way to drive away frightful memories.
Every time that a colored square appeared on the monitor in front of me, I braced for pain. Early into the 10-minute session as a subject of this experiment, I learned that about half of the times that I saw that square, I received a low-voltage shock, via a bar strapped to my right wrist. I also learned that every time I saw a square of a different, "good" color, I could momentarily breathe easy. But in the second day's session, as I watched the squares appear in random order, no shocks punctuated either the "bad" or "good" colors. After several minutes I started to relax.
The researcher conducting this fear conditioning experiment at New York University's Department of Psychology, David Bosch, was monitoring my fear responses. Changes in how much I was sweating, which he gauged by measuring the electrical conductance of the skin on my left middle finger, indicated my fear level. On the first day I was conditioned, like Pavlov's dog, to sweat at the sight of the "bad" color. But that response faded over the course of the second, shock-free session as my fear was "extinguished," a process known as extinction. As Bosch explains, "extinction is learning a new contingency."
"You've created a second memory, with extinction, that competes with the first," says Elizabeth Phelps, director of the lab in which Bosch is conducting his study. But this original memory is very difficult to supplant because, as Phelps explains, it is stored in an almond-shaped region of the brain, the amygdala, which responds to emotional stimuli. Even after time goes by, when people are reminded of a stimulus that they once associated with fear, the fearful memory gets conjured before the non-fearful one.
But perhaps the fear can be shaken once and for all. A recent study led by Phelps found that reminding people of the fearful stimuli, minus any fear-inducing event, shortly before the extinction session can effectively block the first memory. The finding could help improve therapies for overcoming fear.
In this study, published in the December 10 issue of Nature, researchers conditioned 65 participants to fear a "bad" color square the first day and then extinguished their fear the next day, just as in Bosch's study. The scientists waited a day between sessions because it takes hours for a new memory—in this case, the memory of a color being associated with pain—to consolidate in our minds. Before the extinction session, the researchers gave some of the participants a fear-provoking reminder by showing them the "bad" square, though without the unpleasant shock. Twenty-three of the participants received the reminder six hours before the session, while 20 were reminded just 10 minutes before the extinction trial. The rest of the participants did not receive a reminder before the session.
All of the participants were afraid of (as measured via sweaty fingers) the "bad" square at the outset of the first extinction session, before the fear subsided. The extinction trial was repeated on the third day, and the researchers noticed that at the outset of this second extinction trial, those who had had the shock-free reminder 10 minutes before the session were much less afraid than either the 6-hour group or the group that did not receive a reminder. In fact, Phelps's team followed up one year later with 19 of the original 65 participants and found that fearlessness persisted only among those who had received the reminder 10 minutes before the extinction session.
"To show this lasts a year shows us we are perhaps in a permanent way altering this memory," Phelps says.
The mechanism for the initial memory's defeat could be that the initial quick reminder induces the amygdala to store new information, Phelps explains. The window during which the amygdala is "open" is fleeting, however, and could explain why the reminder shown 10 minutes, but not six hours, before the first extinction session, eradicated fear. As Phelps notes, relearning a memory, also known as reconsolidation, takes place much faster, within several minutes, than learning the memory for the first time, or consolidation.
Although more research must be done, Phelps says that these findings suggest that "we could time therapeutic intervention at a time when [patients] are open to reconsolidation." For example, a "reminder" stimulus not associated with fear could be incorporated into counseling within the window of time for reconsolidation. Current therapies for anxiety patients include extinction sessions, though studies have found that this approach does not always prevent the fear from returning.
Another approach that could help reduce fear, though perhaps not prevent it, is being explored by Bosch, who was not involved in the Nature study. He and his collaborators are studying if there is a difference between meditators and non-meditators in how quickly fear subsides during the extinction session. People who practice certain types of contemplative practices may be able to more quickly get the better of their fear, even without a reminder stimulus.
For me, a non-meditator and non-recipient of the reminder stimulus, it took at least a few minutes to subdue my anxiety as I awaited the follow-up shocks that never came. Even though the shocks were more irritating than painful (not unlike the feeling of tapping your funny bone), I am surprised by how indelibly they taught me to fear the color square that was associated with them. I can still picture the image. And I bet that I would still feel anxious for a few minutes if I went back for an extinction session a year from now.
[The exact colors of the squares are being withheld at the researcher's request because the study is ongoing and depends upon unbiased subjects.]