Humans have a six-hour window “to erase memories of fear” BBC News has reported. The news service says that reliving a harrowing memory can trigger a brief period when the mental associations of a memory can be changed from bad to good.
The study that produced these findings took healthy volunteers and induced fear using mild electric shocks. While given these shocks they were shown a particular coloured square on a screen to try to create a mental association between the image and fear. The researchers found that in a six-hour period they could ‘rewrite’ this fearful association by showing these images again without the shocks, but only if volunteers were reminded of their fearful event just before starting this retraining.
This type of laboratory-based study in healthy individuals can help scientists to understand how fearful memories are formed and whether their associations might be altered. However, experiments of this type may not be fully representative of what happens when a person experiences phobia, real-life trauma or a medical condition such as post-traumatic stress disorder. A lot more research will be needed to determine if the results of this study can help people with real-life problems or medical conditions relating to fear.
Where did the story come from?
Dr Elizabeth Phelps and colleagues from New York University and the University of Texas conducted this research. The study received funding from various sources including the James S. McDonnell Foundation and the National Institutes of Health in the US. The study was published in Nature, the peer-reviewed scientific journal.
BBC News, The Daily Telegraph, The Independent and The Guardian covered this research, generally reporting it well. The suggestion by The Telegraph that the researchers could “remove fear and trauma permanently” is a slight overstatement, as the mild shocks delivered in this study would probably not be considered trauma, and the participants of this study were only followed up for one year.
What kind of research was this?
This was a non-randomised controlled study in humans looking at whether fearful memories can be “updated with non-fearful information”. After memories are formed they are reinforced every time they are recalled, a process called reconsolidation. Some studies have suggested that memories can also be suppressed and possibly erased if certain drugs are given during the reconsolidation period after a memory has been recalled. The researchers wanted to test whether they could achieve this same effect without the use of drugs.
Studies of this type, which are carried out in the laboratory setting with healthy individuals, can help scientists to understand how fearful memories are formed and whether the effects of these memories can be changed.
However, experiments like this in a laboratory may not be fully representative of what happens when a person experiences fear in a real-life situation, particularly a traumatic one, or what happens in people who have a medical condition such as post-traumatic stress disorder. A lot more research will be needed to determine whether the knowledge gained from this study can be used to help people with problems or medical conditions relating to fear.
What did the research involve?
The researchers recruited 71 volunteers, who were split into three groups. All groups had electrodes and electrical monitors attached to the skin of their wrist to indicate how much they were sweating, which was taken as an indicator of their fear response. They were then sat in front of a computer monitor and shown two different coloured squares. They were given an electrical shock about one in three times when they saw one particular colour, but were never given a shock when they saw the other colour.
A day later all of the volunteers went through a phase called memory extinction in which they were shown the images again but this time without the shocks. Prior to this exposure the participants had been split into three groups, with two groups being given memory reactivation by being shown the shock-related image and shocked again. One of these groups had reactivation 10 minutes before the memory extinction phase, and the other six hours before.
Twenty-four hours later all three groups went through a ‘re-extinction’ phase in which they were shown the images again, also with no shocks. The responses of the three groups in this final test were compared to see which group was most fearful. The researchers only included the 65 individuals (ages 18 to 48 years, 41 women and 24 men) who had both a fearful response to the first set of shocks and a reduction of this response in the memory extinction tests.
The researchers also asked the volunteers to return after one year to see if their fear response remained the same. Only 19 of the 65 volunteers returned for assessment after one year. Due to the small numbers, the researchers’ analyses pooled the group that had been reminded of their fearful memory six hours before memory extinction with those who had not been reminded. During this set of follow-up tests the researchers looked for fear responses when the volunteers were exposed to four shocks without seeing the images and then shown the shock-associated images from the original experiment.
What were the basic results?
The researchers found that, overall, the volunteers showed a fear response during the initial exposure to the shocks, but this was reduced in the memory extinction phase a day later when they were shown the images without the shocks. There were no differences between the three groups in these periods.
When the volunteers were shown the images for the third time (re-extinction):
- Fear returned in those who had not been reminded of the fearful memory before the first memory extinction
- Fear returned in those who had been reminded six hours before
- Fear did not return in those who had been reminded 10 minutes before the first memory extinction
At one year after the initial experiment, the researchers found that exposing volunteers to shocks and then the associated image:
- Reinstated fear in those who had not been reminded of the fearful memory before the first memory extinction (seven people)
- Reinstated fear in those who had been reminded six hours before (four people)
- Did not reinstate fear in the volunteers who had been reminded 10 minutes before the first memory extinction (eight people)
How did the researchers interpret the results?
The researchers concluded that their findings show that there is a window of opportunity in which emotional memories can be ‘overwritten’ by reconsolidation with non-fearful information. They say that this suggests that a similar non-invasive technique could be safely used to prevent the return of fear in humans.
This study has illustrated that it may be possible to ‘overwrite’ fearful memories; however, there are a large number of limitations to this conclusion:
- The fearful memories assessed in this study were developed in a laboratory setting and related to a mild electrical shock, and may not be representative of real-life fears, particularly those developed from a very traumatic experience.
- It is not yet clear how these techniques could be adapted for use in people with actual phobias or post-traumatic stress disorder. In this experimental situation the fear-inducing event, that is the shock, was paired with an associated image, and then the shocks removed during memory extinction. With some phobias, for example fear of spiders, it is not clear how the fear-provoking event and the visual stimulus (the spider itself) could be separated.
- The study estimated fear response by measuring how much the volunteers sweated. Although this is an objective measure, it cannot tell us how the volunteers felt or whether they were scared or not.
- We do not know whether any of the volunteers had conditions such as post-traumatic stress disorder or phobias. Therefore, it is not possible to say whether these findings apply to people with these conditions.
- Very few people were followed up at one year. The results for this small group may not be representative of the entire sample, and therefore these results should be interpreted very cautiously.
- The study did not use randomisation to assign participants to particular study groups. This means that the groups may have differed in factors other than the treatment received and these factors may have affected the results.
Overall, these results are likely to be of interest to the scientific community, but at the moment there are no practical implications for the treatment or prevention of fear, whether as post-traumatic stress disorder or phobias.