Psychologists find a drug-free way for fears to be unlearned

In an exciting breakthrough for psychological science, researchers in the United States have demonstrated a drug-free way to prevent the return of a learned fear. Similar memory modification effects have been observed before, but these experiments have involved drugs such as the beta-blocker propranolol. It's hoped the new drug-free procedure will lead to improved therapeutic techniques for people with phobias or intrusive traumatic memories.

Elizabeth Phelps and her colleagues exploited the fact that memories are particularly vulnerable to modification just after they've been recalled. The procedure began with 65 participants learning to fear a coloured square that appeared on a computer screen. Each time the square appeared they received a mild but unpleasant electric shock to their wrist. In a real-life scenario the equivalent might be a repeatedly bad experience on each attempt at giving a class presentation.

The next day, the participants were repeatedly presented with the square but without the shock. This is a well-established procedure in psychological therapy known as extinction, the idea being that the person unlearns the fear associated with the stimulus or situation. A real-life equivalent might be to repeatedly practice giving a presentation in a safe environment, perhaps to sympathetic friends and family, or to a "virtual audience".

Crucially, a minority of participants undertook the extinction trials just ten minutes after they were given a reminder of the coloured square. This reminder will have rendered the memory of the square temporarily "labile" or vulnerable to modification. Other participants completed the extinction trials six hours after a reminder - too late to capitalise on the memory's vulnerable period - whilst a third group of participants had no reminder at all.

A short-coming with extinction therapy is that even after people appear to have unlearned the fear associated with a stimulus or situation, that fear can creep back. In the lab, on day three, the participants were again presented with the coloured square. Even though they'd all responded without fear at the end of the previous day's extinction training, the majority of the participants - those who'd had the 6-hour reminder before extinction, and those who'd had no reminder - showed a renewed fear response (as betrayed by their sweatiness), just as eventually tends to happen after extinction therapy in real life.

But excitingly, this was not so for the participants who'd had the ten-minute reminder before the previous day's extinction trials! They were ice calm, unmoved by the coloured square. For this group, it's as if their memory of the square had been permanently modified. When, on the previous day, they'd been reminded of the unpleasant shock-square experience, this memory was briefly vulnerable to modification, and it was just at this critical time that they'd had the run of ten innocuous, shock-free presentations. For the fictional student with a fear of class presentations, the trick would be to recall their nightmare experience in class, and then begin the safe, innocuous practice of presentations with friends.

This study gets even more impressive because the result carried over when a subsample of the participants were retested a year later - those who'd had the ten-minute reminder before extinction were still largely unmoved by the square whereas the other participants again showed signs of fear.

What's more, the intervention is highly specific. The researchers repeated the procedure but with three differently coloured squares - two associated with a shock, and one safe square. They then used the pre-extinction reminder procedure for one of the feared squares but not the other, and it was only this targeted square that remained fear free.

Phelps said: "Previous attempts to disrupt fear memories have relied on pharmacological interventions. 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.”

Phelps also told the Digest that any concerns that their procedure could be abused - for example to erase eye-witness memories or implant false memories - are misplaced. The types of emotional memory that were modified in the current study are represented in the amygdala, whereas the "declarative" memories involved in eye-witness testimony have a different neural representation, she explained. Indeed, all the participants in the current study were able to remember that the coloured square had previously been paired with a shock, it's just that those who undertook extinction ten minutes after a reminder no longer showed an automatic fear response to the square. "In short," Phelps told us, "eyewitness testimony depends on identifying (recollecting) what occurred before. We are not affecting that kind of memory."
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D Schiller, M-H Monfils, C Raio, D Johnson, J LeDoux & E Phelps. (2009). Preventing the return of fear in humans using reconsolidation update mechanisms. Nature

Update: Nature has a free video about this research and a PDF of supplementary methodological info.