Researchers block fearful memories

Scientists have for the first time blocked fear memories in people using behavioural training rather than the drugs usually used in fear therapy.

Scientists have for the first time blocked fear memories in people using behavioural training rather than the drugs usually used in fear therapy.

In a small study involving 65 people, researchers at New York University found that a Pavlovian fear response could be blocked if the subjects underwent a psychological technique called extinction training within hours of the incident that caused the fear.

If the training was received after six hours, however, the memory and fear response remained. The research was published this week in the journal Nature.

"Our research suggests that during the lifetime of a memory, there are windows of opportunity where it becomes susceptible to be permanently changed," said the study's lead author, Daniela Schiller.

"Our results suggest a non-pharmacological, naturalistic approach to more effectively manage emotional memories," New York University's Elizabeth Phelps said.

The researchers induced a fear response in the participants by showing them a series of coloured squares and intermittently giving them a mild shock on the wrist.

The people eventually showed an involuntary fear response to the coloured squares, even without the shock, as a result of this conditioning. Researchers measured the fear response by monitoring changes in the electrical conductance of their skin.

The subjects then underwent extinction training, which involves exposing them to the object of their fears — the coloured squares — in a safe environment, without the shocks.

Some of the subjects received the training within six hours of the fear conditioning while others received it after six hours had elapsed.

The fear response was blocked in the people who received extinction training promptly after the fear conditioning, while those who received it after six hours were still afraid of the coloured squares, though the fright eventually wore off over a longer time.

In a follow-up experiment conducted about year later, researchers tried to reactivate the fear response in 19 of the original participants by shocking them four times and then showing them the squares.

The fear memory didn't return in those who had undergone extinction training within six hours of the fear conditioning, while those who received delayed training were once again afraid of the squares.

The researchers theorize that memories are flexible within a period of a few hours after an event until they are stored again in the brain in a process called reconsolidation.

If psychological techniques such as extinction training are used in the window of time before reconsolidation, the memory can be permanently altered, they said.