Remarkable news on the memory-erasure front. A team led by Elizabeth Phelps at New York University published a report in Nature last month about a technique for wiping out unpleasant associations by taking advantage of a psychological process known as reconsolidation. A good deal of research has gone on lately into the erasure of unpleasant memories, with the goal of treating people suffering from anxiety and PTSD, but so far the focus has been on using drugs, as I've described earlier.
This kind of emotional memory is processed in the amygdala, a crucial hub for coordinating the brain's response to danger. Fear memories can be problematic because, unlike the conscious, "explicit" memories that are formed via the hippocampus -- things like the name of a friend, or the number of pints in a gallon -- they do not fade with time in the same way. As I write in Chapter 10 of Extreme Fear:
The amygdala’s memory system retains frightening associations permanently. If you’ve been bitten by white dog, your amygdala will never forget. But the memory can get overlaid by a positive or neutral association. If you later buy a friendly white dog, say, and spend day after day associating your pet with harmless fun, in time your fear of white dogs will be overlaid by a suppressing response generated by the medial prefrontal cortex. Your amygdala isn’t forgetting that white dogs are dangerous, but you’ve laid a new memory on top of it, like a linoleum floor over a trap door. The old unconscious fear connection remains, encoded subconsciously in the amygdala. Under stress, the buried fear can spontaneously reemerge.
In her study, Phelps explored the effect on extinction of reconsolidation, an intriguing effect in which a memory that has been recalled into consciousness becomes temporarily malleable and subject to change. Previous experimenters have administered drugs, such as the beta-blocker propranalol, during the reconsolidation phase, and found that this can help erase painful memories. Phelps' experiment was designed to see whether a similar effect could be obtained without the use of drugs. And the surprising answer was yes.
As described on the ever-insightful BPS Research Digest blog, Phelps sat her subjects in front of a computer screen and showed them blue and yellow squares. Day One was "acquisition phase," during which the colored squares were paired with painful electrical shocks. (Or not, in the case of the experiment's control subjects.)
Now that the bad memories were firmly in place, the experiment moved on to phase two: extinction training. On the second day, subjects were shown the colored squares in the exact same setting, but this time the image of the squares was not paired with the application of painful shocks. The real-life equivalent would be seeing a white dog after having been bitten by one. Gradually, you learn not to be afraid, but the emotional memory remains, subconsciously, able to return.
This is what the experiment found on day three, when the subjects were once again put in front of the screen and shown the colored squares. Even though they'd successfully completed the extinction training the day before, they nevertheless showed phsyiological evidence of a heightened fear response, such as sweaty palms. Though it had been damped down, the fear remained.
Here's where the ground-breaking part of the study comes in. On day two, just prior to the extinction training, a subset of the subjects were shown an image of the colored squares on the computer screen. Then they went off to watch television for ten minutes, before coming back and taking part in the extinction training. The idea was that this brief reminder would be enough to activate the process of reconsolidation -- to make the fear memory plastic, so to speak, so that extinction could not only over-write the fearful memory, but actually erase it. And it seems that this is exactly what happened. On day three, those subjects who'd had the reminder ten minutes before extinction training showed no signs of fear at the colored squares. What's more, the effect persisted when the subjects were called back into the lab a year later.
As with the propranalol studies, these findings point the way to more effective treatment of patients suffering from traumatic memories. What's more, they suggest a technique that all of us can use to deal with fear in our daily lives, by increasing the effectiveness of home-brew extinction training. If you've had a phobia-inducing bad experience while speaking in front of a class, for instance, you can help extinguish that fear by practicing your presentation in front of a small group of friends. And to make the session even more effective, initiate reconsolidation by looking at the classroom lectern beforehand -- or even just imagining it.
(Parenthetically, Discover magazine recently posted a story on their website about one of the researchers involved in Phelps' work, Daniela Schiller. When people say that NYU researchers are the rock stars of neuroscience, they mean that literally.)