Temporarily returning the brain to a child-like state could help people with post-traumatic stress disorder and phobias forget their fears forever.
A clue to permanent erasure comes from research in infant mice. With them, extinction therapy completely erases the fear memory, which cannot be retrieved, reports New Scientist.
Identifying the relevant brain changes in rodents between early infancy and the juvenile stage may help researchers recreate aspects of the child-like system and induce relapse-free erasure in people.
One of the most promising techniques takes advantage of a brief period in which the adult brain resembles that of an infant, in that it is malleable. The process of jogging a memory, called "reconsolidation", seems to make it malleable for a few hours. During this time, the memory can be adapted and even potentially deleted.
Daniela Schiller at New York University and colleagues tested this theory by presenting volunteers with a blue square at the same time as administering a small electric shock.
A day later, Schiller reminded some of the volunteers of the fear memory just once by presenting them with both square and shock, making the memory active. During this window of reconsolidation, the researchers tried to manipulate the memory by repeatedly exposing the volunteers to the blue square alone.
What's more, their memory loss really was permanent. Schiller later recalled a third of the volunteers from her original experiment.
"A year after fear conditioning, those that had [only] extinction showed an elevated response to the square, but those with extinction during reconsolidation showed no fear response," she said.
The loss in infant mice of the ability to erase a fearful memory coincides with the appearance in the brain of the perineuronal net (PNN). This is a highly organised glycoprotein structure that surrounds small, connecting neurons in areas of the brain such as the amygdala, the area responsible for processing fear.
Cyril Herry at the Magendie Neurocentre in France, and colleagues reasoned that by destroying the PNN you might be able to return the system to an infant-like state.
They gave both infant and juvenile rats fear conditioning followed by extinction therapy, then tested whether the fear could be retrieved at a later date. Like infant rats, juvenile rats with a destroyed PNN were not able to retrieve the memory.
Since the PNN can grow back, Herry suggested that in theory you could temporarily degrade the PNN in humans to permanently erase a specific traumatic memory without causing any long-term damage to memory.
The findings were discussed in the Society of Neuroscience conference in San Diego.