Science fiction has long traded in the idea of memory manipulation. From mass memory editing in Dark City to the more precise memory-wiping of the neuralyzer in Men In Black, there are scores of imaginative stories set in worlds where humans can directly alter a person's memory. Two remarkable new studies are suggesting this sci-fi concept may be entirely possible, describing early proof-of-concept experiments that show how we can enhance or weaken the emotional impact of traumatic memories.

These two new studies focus on conditions such as post-traumatic stress disorder (PTSD), where a negative or traumatic memory has become so powerful it profoundly affects a person's ability to function in day-to-day life. So the challenge is how to manipulate these traumatic memories by finding ways to either suppress them, or edit them by removing any strong, negative emotional attachment.

The memory-wiping drug

The first study examined the effect on memory of a commonly used anesthetic called propofol, which has long been associated with impairing short-term memory. Studies have revealed the sedative has the ability to induce a kind of amnesia in some patients so a team of researchers wondered whether this mechanism could be harnessed to actively suppress emotionally loaded negative memories.

The idea is that when a memory is reactivated it needs to then be reconsolidated in the brain. The process is akin to taking a file out of a filing cabinet, reviewing it, and then placing it back. The hypothesis is that a memory is susceptible to modifications at the point it is being reconsolidated by our brain. So, if administered at a specific moment, it may be possible to use propofol to weaken, or even erase, a negative memory.

To test this a team of researchers took 50 healthy subjects and showed them two different narrative slide-shows. The middle phase of both slideshows contained emotionally negative content designed to prime a negative memory in the subject. One week later the subjects returned to the researchers, and memories of the first slideshow were rekindled and discussed. As soon as this memory was reactivated, the subjects were administered a sedating dose of propofol.

From this point the cohort was divided into two groups. One group was questioned as to their memories of the two different slideshows immediately upon waking, while the second group was asked the same questions but 24 hours later. Interestingly, the group questioned immediately upon waking from sedation reported accurate and unaltered memories of both slideshows, while the group questioned 24 hours afterwards reported vastly different results.

A day after the propofol sedation subjects reported significant impairments to their memories of the slideshow that was rekindled before the sedation, but not to the slideshow that wasn't reactivated. Even more crucially, the subjects' memories of the rekindled slideshow were not completely erased but the impairments were specifically directed at the negative parts of the memory.

This intriguing result demonstrated how negative associations to certain memories can be potentially edited out during a phase of memory reconsolidation and this mechanism can be specifically activated using propofol. Of course, whether these effects hold for longer than 24 hours is still yet to be studied, but the proof-of-concept is solid.

Turning the volume up, or down, on a bad memory

A second new study, recently published in the journal Current Biology, also explored how to potentially edit the negative emotion out of traumatic memories, but this research zoomed in on a different question: what part of the brain could be loading a positive or negative emotion onto a given memory?

The research, led by neuroscientists Steve Ramirez from Boston University and Briana Chen from Columbia University, followed on from previous research finding optogenetic manipulation of cells in a mouse hippocampus can alter behavioral expression of positive and negative memories. The scientists wondered whether different parts of the animal's hippocampus could be associated with different emotional associations to certain memories.

The incredible results revealed a distinct difference in emotional affect between the top and bottom parts of the hippocampus. When memory cells in the bottom of the hippocampus were stimulated, negative experiences associated with certain memories seemed to be significantly amplified. And conversely, stimulating cells in the top part of the hippocampus resulted in memory recall without powerful traumatic emotional associations.

Of course, this particular study is only demonstrating a highly specific mechanism in mouse brains, and the researchers do reasonably admit that mice and human brains are significantly different. However, these results do help better direct scientists in their investigations of specific areas in human brains.

"Let's use what we're learning in mice to make predictions about how memory functions in humans," suggests Ramirez. "If we can create a two-way street to compare how memory works in mice and in humans, we can then ask specific questions [in mice] about how and why memories can have positive or negative effects on psychological health."

From a short-term clinical perspective this research offers incredibly compelling possibilities for future PTSD and anxiety treatments. If the research translates into human brains then the overactive bottom part of the hippocampus may be responsible for a number of different anxiety disorders, and suppressing that particular region could essentially dampen the emotional effect of a traumatic memory.

"The field of memory manipulation is still young … It sounds like sci-fi but this study is a sneak preview of what's to come in terms of our abilities to artificially enhance or suppress memories," says Ramirez.

Admittedly, this research is nowhere near a Total Recall-style form of science fiction memory manipulation where we can literally add false memories into a human brain. Although, researchers are certainly investigating that possibility too, with several studies from the past few years successfully experimenting with ways to implant false memories directly into the brains of mice.

Perhaps the most realistic analogy we have between a futurist film and current research today is Eternal Sunshine of the Spotless Mind from 2004. That film was set in a world where scientists have the technology to accurately delete specific memories, and the story follows a couple who meet up for the second time, after having both undergone the memory erasing procedure. These two new studies raise the provocative prospect that in the future it may be entirely possible to either suppress unwanted memories, or at the very least rewrite any emotional attachment we have to a given memory.

"We're a long way from being able to do this in humans, but the proof of concept is here," concludes Briana Chen. "As Steve [Ramirez] likes to say, 'never say never.' Nothing is impossible."

The propofol study was published in the journal Science Advances.

The hippocampus study was published in the journal Current Biology.