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.

Kate Winslet and Jim Carrey in a scene from the film "Eternal Sunshine of the Spotless Mind." Associated Press

 

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.