Saturday, May 30, 2009

A New Treatment for Phobias and Emotional Trauma?

I have mentioned earlier the recent discovery that when a memory is recalled, it is then re-saved ("consolidated," as researchers llke to say). During that reconsolidation time window, which in rats is about 6 hours, the memory becomes vulnerable to new information and interference, and can become distorted or even abolished.

Researchers have discovered that injecting a beta blocker drug during this reconsolidation period can prevent re-consolidation of the memory that was recalled, and this is an effective therapy for some patients. The problem is that this is a prescription drug and is potentially toxic.

Another approach is to use extinction therapy. Most phobias and emotional traumas arise from a conditioned association between a neutral stimulus and the traumatic event, much like the conditioning discovered by Pavlov and his dogs. If one repeats the conditoning cue, without re-presenting the bad event, the patient may develop a new memory in which the cue becomes innocuous because it is no longer associated with the bad event. The problem here is that the effect can wear off over time, because the original fear memory was never erased.

A new approach has been devised by Marie Monfils, Joseph LeDoux, and colleagues at several neuroscience and psychiatric institutions. Their idea capitalizes on the differences between reconsolidation and extinction. They reasoned that if the non-threatening conditioning stimulus were given deuring the reconsolidation window, a new memory that the situation was safe would be formed. Use of a drug could be avoided.

They tested this idea in rats that were trained to be fearful by pairing a tone cue with electric shock to the feet.This was done three times. The intervention therapy consisted of testing for recall with the tone cue, followed by a series of extinction trials in which the cue was repeatedly delivered without accompanying foot shock. Some rat groups were given the intervention during the window and others outside it, like the next day. The behavioral response of fear was movement freezing. That is, when the tone was sounded, rats indicated their memory of the training by freezing out of fear.

The day after the extinction session, all groups showed a similar abolition of freeze behavior. Extinction worked, but did it last? A month later, the same rats were tested again, and the freeze behavior had returned in all rats except those that had received the neutral cue and extinction training during the reconsolidation window. Multiple other experiments supported the value of this intervention approach.

The investigators are now exploring clinical implications in human psychotherapy. There is a possible negative consequence. Erasing the phobia may be accompanied by the conditioning stimulus acquiring the status of being safe and not just neutral. Studies on humans can also allow experimenters to study not just the behavioral expression of fear but also allow them to examine the thought processes. The fear memory may still be there, with the major change being in the behavioral expression.

Source:
Monfils, M.-H. et al. 2009. Extinction-reconsolidation boundaries: key to persistent attentuation of fear memories. Science. 324: 951-955.

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