Scientists interested in studying memory have long known that humans are poor recorders of life experience. Very often we implant a “false memory” in our own brains, remembering things that never happened or, at least, recalling them differently. The darker side of human memory, however, are those memories we can’t forget. This has prompted scientists to investigate the possibility of someday deleting memories, allowing trauma victims and sufferers of post-traumatic stress disorder (PTSD) to erase their troubled pasts and regain clarity.
Experimenters routinely use mice in their tests of memory, as the differences between the two species are effectively nil at the desired level of brain activity. While it’s decidedly harder to transfer results between us and the lab-friendly rodent, mouse tests have offered a wealth of knowledge regarding brain function during memory formation, and subsequently, deletion.
One 2005 study, for example, found that medical-surgical patients given cortisol during their hospital stays experienced less frequent cases of PTSD, due to the way cortisol blocks the brain’s ability to access memories of fear.
One of the landmark findings occurred earlier this year, when scientists from Emory University, University of Miami, and Scripps Research Institute discovered that the chemical compound SR-8993 may have translational effects in humans based on research on mice under stress. SR-8993 pushes one, but not all, of the molecular buttons that control the brain’s response to certain opioids, such as morphine and oxycodone.
"At first glance, one might infer that the main mechanism by which morphine is working is through pain reduction, but our results lead us to think it could also be affecting the process of fear learning," Kerry Ressler, senior author and professor of psychiatry and behavioral sciences at Emory’s School of Medicine, said in a statement.
Study co-author Thomas Bannister, researcher and assistant professor of medicinal chemistry at Scripps Research Institute, added that an examination of mouse behavior would provide a reliable correlation to how human brains would respond under similar circumstances. "We hypothesized that the fear and anxiety component of addiction relapse may be related, in terms of brain chemistry, to the anxiety felt by PTSD patients,” he said.
After looking at which genes activated in the mice’s brains when researchers exposed them to stress — the mice were strapped to a small wooden board for two hours — the scientists introduced some of them to SR-8993. These mice, the researchers found, had impaired “fear memory consolidation.” They were less able to remember the traumatic experience as a result of the compound’s presence.
"We think SR-8993 is helping to promote a natural process that occurs after trauma, preventing fear learning from becoming over-represented and generalized," Ressler said, adding that SR-8993 works primarily in Oprl1 (opioid receptor-like 1) in the amygdala, the region of the brain responsible for fear learning. “Our model is that in PTSD, the Oprl1 system is serving as a brake on fear learning, but that brake is not working if prior trauma had occurred." In other words, mice were still able to experience fear from sounds and shocks, but the memories of those fears vanished within roughly two days. Mice that hadn’t been given the compound were prone to anxiety-like symptoms and fear, which the team likened to PTSD in humans.
This study holds promising implications for human treatment of PTSD. Scientists that can erase the fear of certain memories may even be able to replace the memory with a more desired false one. MIT researchers moved one step closer with their recent success in implanting memories into mice. Though the team instilled a fearful memory, the researchers suggested the brain’s unreliability could actually work in people’s favor. In other words, why not turn trauma into a false memory, one that is instead happier and pleasant. Given that 70 percent of adults in the U.S. have experienced at least one traumatic episode in their lives, or some 223.4 million people, it may be worth a shot.