Scientists have demonstrated “proof of principle” that traumatic memories can be erased from the brain — as seen in the science fiction film, Eternal Sunshine of the Spotless Mind.
Studies in mice demonstrated that fearful memories prompted by a sound associated with an electric shock could be turned off and on. The researchers said, however, that attempting to experiment on humans was full of ethical problems and some way off. But their studies suggest it will be possible at some point in the future, for example, to treat people suffering from post-traumatic stress disorder or drug addiction.
Speaking recently at the annual meeting of the American Association for the Advancement of Science in Boston, Sheena Josselyn said that they had been able to discover the specific brain cells where a particular memory was stored. “So we can target where in the brain a memory has gone,” she said. “We can then decrease the activity in these cells … And it is as if we erase the memory.” After this was done, the mice were unperturbed when they heard the sound they had previously learned to associate with the shock.
Increasing the cells’ activity restored the memory of the shock — enough to be unpleasant but not to cause lasting harm — to the mice. “We can turn memory on and turn memory off,” Josselyn said, “It really does give us proof of principle. If there’s a memory problem, we don’t have to target the entire body or the entire brain.”
Josselyn, of Toronto University, said that it was possible that in the future scientists could develop “a heat-seeking missile or a heat-seeking drug that would somehow operate on just the cells important for this memory”. “We can erase a fearful memory in mice, suggesting in people there might be a way of targeting just those cells that are important in just this traumatic memory and perhaps getting rid of it,” she said. “The spotless mind,” interjected Professor Howard Eichenbaum, director of the Centre for Memory and Brain at Michigan University, who was taking part in the same briefing to the press at the meeting.
In Eternal Sunshine of the Spotless Mind, an estranged couple erases memories of each other after breaking up, but things do not go quite to plan. Eichenbaum cautioned that there were a limited number of brain cells involved in such memories and killing off one memory might damage others. But he added, “If this memory was particularly severe and was destroying your life, then it might be a reasonable compromise.”
Asked about the ethical considerations, Josselyn said that being able to target the potential treatment was a key issue, adding that she did not see a future in which brain cells would be killed off to remove memories. “The ethics are a really important question. I think we are the sum total of our memories,” she said, “We all learn from our mistakes. If we erase the memory of our mistakes, what is to keep us from repeating them?”
But she added, “For something that really interferes with your everyday life, I think a treatment that targets just those cells could be appropriate.” In addition to removing fearful memories, the researchers have been able to get rid of memories associated with taking cocaine among the mice, suggesting this could lead to new ways of treating drug addicts.
Memories are stored in what is known as an engram, which consists of brain cells that fire in a particular pattern. When something happens, the brain cells, or neurons, compete against each other to store the memory. Josselyn said, “We showed that if two related events occur in a small time window — six hours — then the same neurons win the competition for allocation to both engrams.
“This links the two related memories. If, on the other hand, two events occur more than six hours apart, non-overlapping populations of neurons are recruited and the memories are kept separate.
“Our results suggest that this neuronal competition during memory formation is a mechanism that links or disambiguates related emotional memories.”