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Bad memories lost to the ether

Sun, 30th Mar 2008

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A new study has shown that a whiff of anaesthetic might be able to wipe away bad memories and even prevent post-traumatic stress disorder.

The first use of ether as an anaesthetic in 1846 by the dental surgeon W.T.G. MortonWriting in PNAS, UC Irvine scientists Larry Cahill and Michael Alkire describe how they gave volunteers either small amounts of the inhalational anaesthetic sivoflurane, at a dose one-tenth of that needed to induce unconsciousness, or a placebo. The subjects were then asked to look at a batch of 36 photographs. Some of the images were of a harrowing nature, showing severed limbs for instance, whilst others were relatively humdrum, such as a cup of coffee.

A week later the volunteers were asked to recall as many of the images as they could. Placebo-treated individuals remembered 29% of the harrowing images and 12% of the more boring ones, but the sivoflurane group recalled just 5% of the harrowing pictures and 10% of the boring ones. Brain scans show that sivoflurane can interfere with communication between the amygdala - the part of the brain concerned with emotion and fear - and the hippocampus, where new memories are laid down, thus explaining why the anaesthetic-treated group recalled far fewer of the emotionally-harrowing images than volunteers given the placebo.

The team suggest that understanding how blocking this pathway affects memory formation could also be used to treat people at risk of developing post-traumatic stress disorder, a condition in which patients experience vivid and emotionally-charged flashbacks of frightening or stressful situations.

For people who already have the condition though the problem might be more difficult to solve, although New York University researcher Joseph LeDoux has  found that rats that have learned to associate a sound with receiving an electric shock can be pursuaded to forget the association if they are played the sound whilst under the influence of a drug that can affect memory. This suggests that, in the same way, perhaps PTSD patients could be prompted to re-live their ordeals whilst under the influence of a low dose of an anaesthetic to help them to forget their unpleasant experience.

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