50 years ago many scientists thought it was impossible.
A research group guided by Marijn Kroes from Radboud Universiteit Nijmegen developed a system to remove unpleasant memories of selected patients, by using electroshock. The result has been published in Nature Neuroscience and could open the door to a new series of treatments.
The first memory eraser
To comprehend the importance of the results obtained by Kroes, it is necessary to have some background knowledge. In 1968 the researcher Donald Lewis tamed some rats to fear a certain sound up to the point where they panicked when they heard it. Then Lewis waited one more day, let the rats hear the sound again, and gave them an electric shock. After the shock, the rats lost their fear: they had removed the negative memory.
The research of Lewis was revolutionary, because it suggested for the first time that memories could be erased , even after some time. Up to then, scientists thought that removal of memories (if possible) could only happen immediately after the memory itself had been created. That is before consolidation, when the image is moved from the short-tem to the long-term memory where they were thought to stay forever.
Although Lewis published his findings in Science, it was not a big success in the scientific community. Many researchers were not convinced, because a similar study conducted a few years later did not show the same results.
Only at the end of the Nineties, neuroscientist Karim Nader from NY University gave birth again to the topic. He showed that old memories in rats could be removed by injecting a drug when a particular memory is activated. The chemical substance blocks the synthesis of some proteins involved in the memory mechanisms.
Taking it a step further
Now Kroes, from the school of Nader, tried the trick on humans. His research included 39 persons affected by strong depression, already having undergone cycles of electroshock. Despite its bad reputation in the public, because of scientist abusing this technique during the first years of 1900, electric shock is still a common therapy to treat severe cases of depressions. It is used on patients that did not respond to any other therapy and is carried out under full anesthesia.
In order to find out whether electroshock could remove negative memories, Kroes prepared a simple test. The patients were shown two series of photographs with two different stories. In the first, two sisters are walking on the street to visit their brother when a men kidnaps one of two girls and threatens her with a knife on her throat. In the second, a kid is hit by a car and a surgeon has to reattach his foot. Two unpleasant stories with a high impact for people affected by severe depression.
After one week the same patients were shown the same pictures, in order to recall the bad memories. After a few minutes some of the patients were treated with electroshock. All the subjects then answered a multiple choice test about the two stories.
The people that did not get electroshock treatment answered correctly to around half of the questions. This was quite different for those that were treated with electroshock. These people did not seem to remember the “bad stories” anymore: they answered correctly to only 25% of the questions. That is the same result we can expect when answering randomly. The patients who had not been showed the images again before electroshock performed better.
Although the experiment was very successful, there are still some doubts to be clarified. The researchers cannot exclude that the negative memory could have been erased by anesthesia. Moreover it is not clear whether Kroes’s system could also be applied to older memories, with stronger roots in our mind.
Many media spreading the news cited the 2004 film “Eternal Sunshine of the Spotless Mind” by Michel Gondry. Its plot reminds us of what the research of the team of Kroes realized. The film tells the story of Clementine (Kate Winslet) and Joel (Jim Carey), who after a complicated relationship decide to split up. In order not to suffer from the memories of their relation, they both use the services of Lacuna, a society that developed a system to cancel selected memories of people.
Kroes is now working, together with his colleagues, on other experiments and he hopes to start a series of clinical tests soon. He will use electroshock to try to remove traumatic memories of patients who suffer from post-traumatic stress. Still many years of study will be needed before developing a therapy, however. If it will ever be possible.
Photo: Flickr, aenimation
Kroes MC, Tendolkar I, van Wingen GA, van Waarde JA, Strange BA, & Fernández G (2013). An electroconvulsive therapy procedure impairs reconsolidation of episodic memories in humans. Nature neuroscience PMID: 24362759
memory, erase, long term, electroshock, brain