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Saturday, February 28, 2009

Erasing Fear Memories

I have discussed elsewhere a new idea for treating unpleasant memories, such as post-traumatic stress syndrome. The latest treatment being investigated by some researchers is based on using a common blood pressure drug, propranolol, which has a side effect of blocking the re-consolidation of emotions associated with old memories when those memories are recalled.

The original idea was first confirmed in rats. Now a study indicates that the approach can work in humans and might become a clinically valuable treatment. In this human study, subjects were given a mild shock when shown pictures of spiders on the first day of the study. Their fear response was measured as the eyeblink startle reflex to a loud noise. On day 2 of the study, the memory reactivation phase, the study volunteers exhibited the same response to the fearful stimuli (the spider pictures) as on day 1. On day 3, 20 of the subjects were given 40 mg of propranolol, and the remaining 20 were given a placebo. Next, the entire group was exposed to the fearful stimuli. The propranolol group did not exhibit the same startle response as on previous days. The placebo group showed no change in startle response compared to days 1 or 2. In other words, the drug reduced the emotional response, yet did not reduced the memory of the learned event.

Thus, it seems that if propranolol is in the body at the time when one recalls a bad memory, the emotional impact of the memory can diminish without impairing the ability to remember the item. Psychiatric treatment protocols remain to be worked out. Notice that in this situation the learned fear response was recent. Nobody knows if this effect occurs with old, well-entrenched fear memories. Another issue that nobody seems to be asking is the possibility that people on this kind of blood pressure medication might be suffering impairments of emotional memories that they don't want to lose. Does this drug cause a general dulling of emotions?


Merel Kindt, Marieke Soeter, Bram Vervliet (2009). Beyond extinction: erasing human fear responses and preventing the return of fear Nature Neuroscience DOI: 10.1038/nn.2271

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