Memory erasure is the stuff of science fiction. Now, researchers in The Netherlands have reported that electroconvulsive treatment can erase bad memories in individuals suffering from disorders such as post-traumatic stress disorder, psychiatric problems, mental trauma, and drug addiction. Their findings were published online on December 22 in the journal Nature Neuroscience.
The study group comprised 39 patients who were undergoing electroconvulsive therapy for severe depression. They were shown a troubling story in words and pictures. One week later they were reminded about the story and then were subjected to electroconvulsive therapy; the treatment completely erased their memory of the unpleasant story in all the subjects. In the past, scientists were of the opinion that once a memory was established in the brain, it was permanently stored and could not be altered. Individuals suffering from anxiety disorders were taught to overcome their fears by creating a new memory; however, the old memory remained and could be revived at any time. In rodent studies that were conducted about 10 years ago, researchers found that when an animal was given a reminder of some past fear, the memory of that event appeared to briefly become unstable; however, if nothing was done, that memory stabilized for a second time and ten became ingrained into the conscious memory; the process is termed reconsolidation. The investigators found that when certain drugs, known to interfere with the reconsolidation process, were injected directly into the rodent’s brain, they completely erased the unpleasant memory. Of importance was the finding that other memories remained.
Injecting drugs directly into the human brain was not a viable option for the researchers involved in the current study; therefore, they turned to electroconvulsive therapy. The treatment involved first administering a muscle relaxant and an anesthetic to the patient; then, an electrical current was administered to part of their brains, which triggered a brief seizure. Currently, it is unknown how the therapy combats depression. One theory is that it changes the pattern of blood flow or metabolism in the brain; another is that it releases certain chemicals in the brain that combat the depression.
Electroconvulsive therapy is by no means a first-line therapy; it is only given to patients who do not respond to drug therapy. The study patients were asked to watch two disturbing stories on a computer screen; the stories were presented via a series of pictures and a voice-over. One story was about a child who was 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. One week later, the patients were randomly assigned to one of three groups, A, B and C. In an effort to reactivate an unpleasant memory, each patient was asked to recall details about just one of the unpleasant stories he or she had seen. Group A was given electroconvulsive therapy immediately after the query. A day later, the patients took a multiple-choice test about both stories. They recalled most details about the particular story for which their memories had not been reactivated; however, their recall for the other story, whose memory had specifically been reactivated, was extremely poor. It was similar to mere guessing.
The group B patients also received electroconvulsive therapy immediately after the query; however, their memories were tested immediately after the treatment. Their recall of both stories was intact. This finding suggested that it takes time to impair a memory; this result was predicted by the researchers. Group C served as a control group; they did not receive electroconvulsive therapy. When they were tested, their memories of the stories were actually heightened. This finding suggested that it requires both reactivation and electroconvulsive therapy to prevent reconsolidation; thus, disrupting memories.
The researchers stress that much additional research is needed to determine whether memory erasure is temporary or permanent. Although the treatment appears to be effective for simple stories, it might not work for real-world traumatic memories. The study authors plan to test the drug in approximately 50 patients suffering from posttraumatic stress disorder.