In an early trial, a team of scientists has used the anesthetic propofol to disrupt traumatic, solidified memories in humans, opening the door for its possible use to treat people with post traumatic stress disorder or severe phobias.
Earlier research suggested that drugs like propofol could make it harder to remember the vivid details of traumatic events. But previous efforts to test this in people focused on mostly newer memories that had less time to solidify, says neuroscientist Bryan Strange of the Universidad Politécnica de Madrid, who led the research project.
Strange says newer memories are more labile and more prone to disruption. Scientists long thought that a consolidated memory—one that the brain has had time to replay and store—was too entrenched for drugs like propofol to disrupt. But these types of memories are often the problem for people with PTSD or a long-term phobia. “Now, the standard view of memory is that this is not possible,” Strange says. “After a period of consolidation, memory becomes relatively stable, or fixed.”
But earlier findings in rodents challenge this idea, Strange says. In those studies, researchers reactivated the traumatic memory in the animals, making it labile to treatments that then disrupted the memory. These treatments, which use protein synthesis inhibitors, are toxic and aren’t practical for use in people.
Strange and his colleagues wanted to try the same reactivation approach but paired with a drug that would do the memory disruption. The research team recruited 50 people who were already scheduled to be anesthetized using propofol for an endoscopy. The scientists split the participants into two groups. One group watched a video that was emotionally neutral until a scene in which a child was kidnapped. The other video was similar, except the traumatic scene involved a car crash. One week later—presumably enough time for the shocking memory to solidify—the study subjects watched part of the video again, were asked questions about its content to determine how well they remembered what they saw, and then immediately received a dose of propofol that would put them into deep sedation for an average of about 12 min.
The researchers split the people into two groups, independent of which video they watched. The researchers tested one group’s memory of the video immediately upon waking up and tested the other 24 h later. The people who were tested 24 h after waking up had a harder time remembering details of the traumatic sections of the video, providing some evidence that their memories had been affected (Sci. Adv. 2019, DOI: 10.1126/sciadv.aav3801).
Strange says the research is in its early stages. Trauma often involves physical symptoms, such as pain, and this study mainly focused on visual stimuli, not physical ones. Truly erasing a traumatic memory may involve more than just erasing the visual components of the memory. And for many people with PTSD, their trauma is years old, he says. These memories will be quite entrenched and likely harder to break up. His team would also like to repeat these experiments with different doses of propofol to find one that is most effective.
The findings hearken back to efforts during World War II to treat soldiers with PTSD through deep sedation, says neuroscientist John Krystal of Yale University, who was not involved in the study. He says that propofol works through two receptors in the nervous system, the GABA-A and NDMA glutamate receptors, which scientists think interfere with consolidation of learning and memory. Strange’s work, he says, provides some support for this idea.
Current treatment for PTSD involves selective serotonin reuptake inhibitors like paroxetine. “They help many people,” Krystal says. “However, large numbers of people with PTSD treated with these medications are either non-responders or partial responders. There is a tremendous unmet need for more effective treatments.”