Unwanted Memories Erased in Electroconvulsive Therapy Experiment
Unwanted Memories Erased in Electroconvulsive Therapy
Experiment
Scientists Search for New Treatments for Mental Trauma
By GAUTAM NAIK CONNECT
Updated Dec. 22, 2013 9:14 p.m. ET
Scientists have zapped an electrical current to people's
brains to erase distressing memories, part of an ambitious quest to better
treat ailments such as mental trauma, psychiatric disorders and drug addiction.
In an experiment, patients were first shown a troubling
story, in words and pictures. A week later they were reminded about it and
given electroconvulsive therapy, formerly known as electroshock. That
completely wiped out their recall of the distressing narrative.
"It's a pretty strong effect. We observed it in
every subject," said Marijn Kroes, neuroscientist at Radboud University
Nijmegen in the Netherlands and lead author of the study, published Sunday in
the journal Nature Neuroscience.
The experiment recalls the plot of the movie
"Eternal Sunshine of the Spotless Mind," in which an estranged couple
erase memories of each other.
Science has tinkered with similar notions for years. In
exposure treatment, repetitive exposure to a phobia in a nonthreatening way is
designed to help patients confront their fears and gradually weaken the fear
response, a process known as extinction. Some researchers also are
experimenting with antianxiety drug propranolol. The hope is that one day it
may be possible to selectively eliminate a person's unwanted memories or
associations linked to smoking, drug-taking or emotional trauma.
Scientists used to think that once a memory took hold in the
brain, it was permanently stored and couldn't be altered. People with anxiety
disorders were taught to overcome their fears by creating a new memory. Yet the
old memory remained and could be reactivated at any time.
About a decade ago, scientists made a surprising
discovery. They showed that when a lab rodent was given a reminder of some past
fear, the memory of that event appeared to briefly become unstable. If nothing
was done, that memory stabilized for a second time, and thus got ingrained—a
process known as reconsolidation.
But when certain drugs, known to interfere with the
reconsolidation process, were injected directly into the rodent's brain, they
wiped out the animal's fearful memory altogether. Crucially, other memories
weren't erased.
Whether it was possible to disrupt the
memory-consolidation process in humans was thought to be difficult to answer
because injecting drugs into the human brain is risky business. Dr. Kroes and
his colleagues found a way around the problem.
Their test subjects were 39 patients who were undergoing
electroconvulsive therapy for severe depression. In ECT treatment, patients get
a muscle relaxant and an anesthetic and an electrical current is passed to part
of their brains, triggering a brief seizure that can help treat the depression.
It isn't clear how the technique works: Some scientists have suggested it
changes the pattern of blood flow or metabolism in the brain, while others
believe it releases certain chemicals in the brain that battle the depression.
Patients who are treated with ECT are those who typically
haven't responded to an array of other treatments, including the most powerful
drugs available.
The 39 patients were asked to watch two distressing
stories on a computer screen, narrated via a series of pictures and a
voice-over. One story was about a child who is hit by a car and has to have his
feet severed by surgeons. The other involved a pair of sisters, one of whom is
kidnapped and molested.
A week later, the 39 patients were randomly assigned to
one of three groups, A, B and C. Each person was prompted to recall details
about just one of the troubling stories he or she had seen—an effort to
specifically reactivate that memory.
Group A was given ECT immediately after. A day later, the
patients took a multiple-choice quiz about both stories. They recalled most
details about the particular story for which their memories hadn't been
reactivated.
However, their recall for the other story—whose memory
had specifically been reactivated—was extremely poor. It was no better than
guesswork, in fact.
Patients in group B were given ECT immediately after, and
their memories were tested immediately after the procedure. Their recall of
both stories was intact. It suggests that it takes time to impair a memory—something
the scientists had predicted.
The 13 members of group C acted as a control group and
didn't receive ECT. When tested, their memories of the stories were actually
enhanced. That suggests that it requires both reactivation and ECT to prevent reconsolidation
and thereby disrupt memories in people.
"It's a clever demonstration and could provide a new
tool for us clinically," said Karim Nader, a neuroscientist at McGill
University in Canada, who wasn't involved in the Nature study.
A lot more work needs to be done. It isn't clear whether
the memory erasure is temporary or permanent. And while the technique might
work for simple stories, it needs to be shown that it also works for real-world
traumatic memories.
Some researchers looking to move beyond ECT are now also
experimenting with propranolol, which inhibits the actions of a hormone that
enhances memory consolidation. This summer, Dr. Nader hopes to test the drug in
about 50 patients suffering from posttraumatic stress disorder.
—Shirley S. Wang contributed to this article.
Write to Gautam Naik at gautam.naik@wsj.com
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