When we learn something, for it to become a memory, the event must be imprinted on our brain, a phenomenon known as consolidation. In turn, every time we retrieve a memory, it can be reconsolidated—that is, more infor­mation can be added to it. Now psychologist Liz Phelps of New York University and her team report using this “reconsolidation window” as a drug-free way to erase fearful memories in humans.

Although techniques for over­coming fearful memories have existed for some time, these methods do not erase the initial, fearful memory. Rather they leave participants with
two memories—one scary, one not—either of which may be called up when a trigger presents itself. But Phelps’s new experiment, which confirms earlier studies in rats, suggests that when a memory is changed during the so-called reconsolidation window, the original one is erased.

Using a mild electric shock, Phelps’s team taught 65 participants to fear certain colored squares as they ap­peared on a screen. Normally, to overcome this type of fear, researchers would show participants the feared squares again without being given a shock, in an effort to create a safe memory of the squares. Phelps’s group did that, but in some cases investigators asked subjects to contemplate their fearful memory for at least 10 minutes before they saw the squares again. These participants actually replaced their old fearful memory with a new, safe memory. When they saw the squares again paired with shocks up to a year later, they were slow to relearn their fear of the squares. In contrast, subjects who created a safe memory of the squares without first contemplating their fearful memory for 10 minutes immediately reactivated their older, fearful memory when they saw a square and got a shock.

The researchers suspect that after calling up a memory, it takes about 10 minutes before the window of op­portunity opens up for the memory to be reconsolidated, or changed, in a meaningful way, Phelps explains. “But there is some combination of spacing and timing that we need to figure out,” she adds—the scientists do not yet know how long the window lasts. Even more intriguing is the role contemplation plays—does sitting and thinking about the fearful memory make it more mal­leable than does simply recalling it? Although questions remain, Phelps and her colleagues hope their work will eventually help people with debilitating phobias or perhaps even post-traumatic stress disorder.