By Maia Szalavitz @maiasz
Dec. 22, 2013
Using electroshock therapy, scientists say it may be possible to get rid of specific emotional memories.
We’re still far from being able to blot out our latest breakup “Eternal Sunshine”-style. But research published in the journal Nature Neuroscience showed for the first time that it may be possible to manipulate human memories with physical interventions such as electricity shortly after they are recalled. The study could lead to new treatments for conditions like depression, post-traumatic stress disorder (PTSD) and even addictions— all of which can involve memories that are intrusive and potentially destructive.
The intriguing experiment involved 42 severely depressed patients who had already agreed to undergo electroconvulsive therapy (ECT), which is typically used as a last resort when all other measures have failed. Since ECT is well-known for having negative effects on recall in general — that’s why it’s reserved for only the most intractable cases— the researchers wanted to see if it might only disrupt a newly formed emotional memory, as well as lift depression.
Led by Marijn Kroes, a postdoc at the Donders Institute for Brain, Cognition and Behavior at Raboud University Nijmegen in the Netherlands, the authors first asked the participants to watch two extremely unpleasant, narrated slideshows. One told the story of a young boy who is hit and killed by a car as he walks with his mother. The other involved two sisters, one of whom is seriously assaulted and molested by an escaped convict.
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Participants were told that the study was focused on memory, and were told to pay close attention to both the images and the stories. A week later, all were shown a partially covered version of its first slide and asked to recall just one of the stories. Then the patients were divided into three groups— two groups were given ECT immediately after recall and testing — one group was quizzed on both stories immediately after waking from the anesthesia used for the procedure while the other was tested 24 hours later. The third group simply got the cue and the test, but not ECT.
The patients who were queried just after waking remembered both stories equally well. The group that didn’t receive ECT actually remembered the story that they had been cued and tested on better— not surprisingly, since they were reminded of it.
The group tested a day later, however, was different. While they were able to remember some of the story that they hadn’t been cued to think about immediately before ECT, they couldn’t recall the one they had been primed to remember before the treatment at all. “They performed no better than chance level,” says Kroes, “They might just as well have been guessing.”
The scientists believe that the timing of the memory testing mattered: the fact that memories could be accessed immediately, but not a day later, suggests that the effect of electricity takes time to interfere with the memory storage process. Far from being the faithful record of the past that we like to imagine it as, memory is actually used by the brain mainly to predict the future— and this means that old memories are vulnerable to being re-written every time we access them. Previous research showed that this time-dependent “reconsolidation” occurs in animals, but this is the first time it has been demonstrated in humans.
Hank Greely, director of the Center for Law and the Biosciences at Stanford University, who specializes in the ethics of neuroscience but was not associated with the study, notes that it’s not yet clear whether the technique would actually work for personal memories, which may be more complex, engrained and layered with emotional and other sensory characteristics that aren’t so easily manipulated—rather than those of a short slide show seen a week earlier in a lab setting. That would make a difference in how such strategies might be used to treat certain mental illnesses — while it might help those who were recently traumatized, for example, if it doesn’t affect older memories, it wouldn’t work in many cases of more established PTSD or the many other disorders oftenrelated to childhood traumas.
Elizabeth Phelps, professor of psychology and neural science at New York University, also cautions that the participants’ overall recall of both stories wasn’t great, making the differences between the groups small. “I think it’s interesting as a proof of concept, but I don’t think it’s necessarily going to be a robust treatment because it’s so invasive,” she says. Phelps was not involved with this research, but Kroes has recently been hired by her lab.
Phelps and other researchers have previously used far less invasive techniques to reduce the emotional charge attached to a memory— rather than eliminating the memory itself. For example, one study exposed participants to smells paired with shocks and then wafted the same scents into their noses as they slept. The volunteers didn’t forget which scent was linked with the shock— but they no longer had a fear response to it. “If you could take away the fear associated with the memory and keep the memory, that would be more optimal,” she says.
Kroes plans to look next at whether having patients deliberately think about their most distressing or traumatic memories immediately before ECT would erase these memories, or at least dampen their impact and improve depression.
If that does work, the potential uses of a technique that erases personal memories raises profound ethical questions. Our memories are deeply related to our selves and many survivors of trauma get a sense of meaning and purpose from knowing what they have conquered. If negative or challenging memories are selectively removed, what would they leave behind?
“What if we wiped out all of the memories of the Holocaust?” asks Greely, “That would be terrible. On the other hand, the suffering caused by some memories is really powerful and I would want to prioritize letting people who want to relieve their suffering, as a general matter, relieve their suffering.”
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Greely is most concerned about how such technologies would be used against people’s will. If a trauma survivor wants to erase bad memories, he thinks it should be permitted— but absolutely not required. However, he can also envision situations in which involuntary use of memory-altering techniques might sometimes be acceptable — for example, parents might request it to protect their child from the legacy of surviving a traumatic event.
Taken to another extreme, such tactics could also be a new way to train spies and soldiers, potentially creating individuals who could commit atrocities without regret. While such professionals are already steeled to the consequences of their actions, the ability to selectively erase potentially troublesome and painful recollections would provide new levels of efficiency that might be disturbing. In legal cases, it could also raise new issues related to the reliability of witness testimony altered by such techniques.
But before that happens, says Kroes, he and others will have to learn much more about how the brain makes, stores and recalls memories. His results suggest that it may be possible to selectively delete some memories from our brains, but more work will be needed to understand what happens to the space that those missing memories leave behind.