A team of Dutch researchers led by Merel Kindt has successfully reduced the fear response. They weakened fear memories in human volunteers by administering the beta-blocker propranolol. Interestingly, the fear response does not return over the course of time.
The findings were published in the March 2009 issue of Nature Neuroscience.
Until recently, it was assumed that the fear memory could not be deleted. However, Kindt's team has demonstrated that changes can indeed be effected in the emotional memory of human beings.
Before fear memories are stored in the long-term memory, there is a temporary labile phase. During this phase, protein synthesis takes place that ‘records’ the memories. The traditional idea was that the memory is established after this phase and can, therefore, no longer be altered. However, this protein synthesis also occurs when memories are retrieved from the memory and so there is once again a labile phase at that moment. The researchers managed to successfully intervene in this phase.
During their experiments the researchers showed images of two different spiders to the human volunteers. One of the spider images was accompanied by a pain stimulus and the other was not. Eventually the human volunteers exhibited a startle response (fear) upon seeing the first spider without the pain stimulus being administered. The anxiety for this spider had therefore been acquired.
One day later the fear memory was reactivated, as a result of which the protein synthesis occurred again. Just before the reactivation, the human volunteers were administered the beta-blocker propranolol. On the third day it was found that the volunteers who had been administered propranolol no longer exhibited a fear response on seeing the spider, unlike the control group who had been administered a placebo. The group that had received propranolol but whose memory was not reactivated still exhibited a strong startle response. The fear response was measured using two electrodes under the eye that measured the eye-blinking reflex. The response measured is one directly initiated by the amygdala, the emotional centre of the brain.
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Cognitive behavioural therapy is currently the prevailing and most effective method for treating anxiety disorders. During such a treatment the patient is exposed to the fear-eliciting stimulus without the feared consequence occurring. This method frequently only achieves short-term results and the fears often return over the course of time.
Interestingly, after the treatment with propranolol and memory reactivation, fear memories can no longer be recalled by means of a much-used method in which the individual pain stimuli are re-administered. This indicates that the anxiety memory is either completely erased or could no longer be found in the memory. It should be noted, however, that the human volunteers could remember the association between the spider and the pain stimulus but that this no longer elicited any emotional response. In the next phase of the research, Kindt and her colleagues shall investigate the long-term effects of administering propranolol.
Treatment of anxiety disorders
The researchers expect that the results from this study can contribute to a new procedure for the treatment of patients with anxiety disorders. The method intervenes in the memory in a completely different way to conventional treatments. Whereas the traditional cognitive behavioural therapies frequently focus on the creation of new memories, this method focuses on the weakening of the existing emotional memory.
In 2007, Merel Kindt received a Vici grant from NWO for her innovative research. This study was carried out by Merel Kindt, Marieke Soeter and Bram Vervliet at the Universiteit van Amsterdam.
- Merel Kindt, Marieke Soeter & Bram Vervliet. Beyond extinction: erasing human fear responses and preventing the return of fear. Nature Neuroscience, 2009; 12 (3): 256 DOI: 10.1038/nn.2271
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