French CNRS scientists in collaboration have shown that a memory of a traumatic event can be wiped out, although other, associated recollections remain intact. This is what a scientist in the Laboratory for the Neurobiology of Learning, Memory and Communication (CNRS/Orsay University), working with an American team, has recently demonstrated in the rat. This result could be used to cure patients suffering from post-traumatic stress.
Recalling an event stored in the long-term memory triggers a reprocessing phase: the recollection then becomes sensitive to pharmacological disturbances before being once more stored in the long-term memory. Is drug therapy capable of wiping out the initial memory, and only that memory?
The scientists trained rats to be frightened of two distinct sounds, making them listen to these sounds just before sending an electric shock to their paws. The next day, they gave half of the rats a drug known to cause amnesia for events recalled from memory, and played just one of the sounds again. When they played both sounds to the rats on the next day, those which had not received the drug were still frightened of both sounds, while those which had received the drug were no longer afraid of the sound they had heard under its influence. Recalling the memory of the electric shock associated with the sound played while rats were under the influence of a drug thus meant that the memory was wiped out by the drug, leaving intact the memory associated with the other sound.
The researchers also recorded the neuronal activity of rats in the amygdale, an area of the brain associated with emotional memory. Neuronal activity increased when remembering the traumatic memory, but diminished in drugged rats. This result showed that pharmacological disturbance of the memory recalled did indeed consist in selectively wiping out this memory, and only this memory. This is the first demonstration that a memory can be modified or even wiped out at the cellular level, permanently and independently of other memories associated with it.
Synapse-specific reconsolidation of distinct fear memories in the lateral amygdale, V. Doyère, J. Debiec, M.-H. Monfils, J. E Schafe, J. E LeDoux, Nature Neuroscience, doi :10.1038/nn1871 (2007). Advanced online publication on March 11, 2007