Research illustrates vulnerability of brain’s information storage
An electrical shock to the brain can muddle a nasty memory. Precisely timed electroconvulsive therapy, a last-ditch treatment for severe depression, interferes with a person’s ability to remember a recently learned story, scientists report December 22 in Nature Neuroscience.
The ECT results are the latest to highlight that memories are fluid, susceptible to manipulation and even destruction. Scientists hope to ease the mental burden of diseases such as anxiety and post-traumatic stress disorder by selectively targeting traumatic memories with behavioral therapy, drugs, ECT and milder forms of brain stimulation.
“We are starting to understand the process, to some extent,” says study coauthor Marijn Kroes of Radboud University Nijmegen in the Netherlands. But, he cautions, “we are a very long way away from treating patients.”
Scientists and patients know that ECT is bad for memory in general, but the results show that the therapy, when carefully timed, can knock down specific memories, Kroes says.
He and his colleagues studied 42 people with depression who were receiving ECT, a treatment that briefly jolts the brain with a powerful electrical current. Participants watched a series of pictures as they heard a narrator describe two disturbing stories. In the first, a car hits a young boy and severs both of his feet. In the second, an escaped convict attacks a woman in an alley.
A week after they first encountered these stories, the participants saw a picture from one of the stories and were asked about it. That exercise triggered a process called reconsolidation that is thought to make a memory wobbly as the brain dredges up the information and stores it again. Immediately after recalling the story, the patients were anesthetized and treated with ECT. A day after that, participants took multiple-choice tests about the story.
People performed no better than chance at remembering the details of the story that had been recalled just before ECT, the researchers found. But participants were better at remembering the story that hadn’t been recalled just before ECT.
Testing patients immediately after ECT instead of waiting a day didn’t reveal a memory deficit. That observation shows that it takes time to weaken a memory.
The results “are very elegant,” says Daniela Schiller of Mount Sinai School of Medicine in New York. But many questions remain, she says. It’s unclear whether ECT could interfere with natural memories, created in a person’s daily life and not in a lab. “There is some evidence that older memories and stronger memories are sometimes resistant” to tampering, Schiller says. It’s also unclear whether the anesthesia plays a role in the memory loss, or how long the effects would last, she says.
While ECT works well for people suffering from severe depression, it may be too extreme to become a widely used treatment to ease traumatic memories. But for people who are already undergoing ECT for depression, the results suggest to a way to preserve memories, Kroes says: If a person could avoid thinking about something right before ECT, that memory might be better protected. Likewise, a person might want to call up unpleasant memories with the hope that they would be selectively weakened.
M. Kroes et al. An electroconvulsive therapy procedure impairs reconsolidation of episodic memories in humans. Nature Neuroscience. Published online December 22, 2013. doi:10.1038/nn.3609.
L. Sanders. Surprise makes memories wobbly. Science News, Vol. 183, March 23, 2013, p.12.