A drug-free way to block fearful memories has been devised by US scientists. This finding opens up the possibility of new treatment approaches for problems such as post traumatic stress disorder.
The findings in humans build on studies in rats that showed that reactivating a memory - by showing people objects that stimulate the fearful memory -opens up a specific time window in which the memory can be edited before it is stored again.
"Our results suggest a non-pharmacological, naturalistic approach to more effectively manage emotional memories," said Elizabeth Phelps, of New York University.
The results add support to the hypothesis that emotional memories are reconsolidated - rendered vulnerable to being modified - each time they are retrieved. That is, reactivating a memory opens what researchers call "reconsolidation window," a time-limited period when it can be changed.
Earlier this year, Joseph LeDoux from NYU and colleagues exploited this potentially clinically important insight to erase a fear memory in rats.
In the new study, Phelps and colleagues conditioned human participants to fear coloured squares by intermittently pairing them with mild wrist shocks.
A day later, the memory was first reactivated by re-exposing participants to the feared squares. A measure of nervous system arousal confirmed that they experienced a fear response. Extinction training - repeated trials of exposure to the coloured squares without shocks - followed.
A day later, the fear response was banished only in human participants who underwent the extinction training soon after the fear reactivation.
Those trained after the 6-hour consolidation window remained afraid of the squares - as did a control group that received extinction training without first experiencing reactivation of the fear memory.
Evidence suggests that the behavioural manipulation may work through the same molecular mechanisms as experimental medications under study for quelling traumatic emotional memories.
"Using a more natural intervention that captures the adaptive purpose of reconsolidation allows a safe and easily implemented way to prevent the return of fear," the authors said.
The study has been published online Dec. 9, 2009 in the journal Nature.