Sometime soon, a lab mouse could wake up thinking he had snuggled up to a girl mouse the night before. But he hadn’t. The memory is fake.
Scientists at the Massachusetts Institute of Technology (MIT) have successfully implanted a false memory into a mouse’s brain, a seemingly far-fetched idea reminiscent of a science-fiction film.
“If mice had Hollywood, this would be ‘Inception’ for them,” said one of the lead researchers, MIT neuroscientist Steve Ramirez, referring to the 2010 sci-fi action movie. The study was published online Thursday in the journal Science.
Ramirez and his colleagues tagged brain cells associated with a specific memory, and then tweaked that memory to make the mouse believe something had happened when it didn’t.
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Although implanting a memory won’t happen anytime soon in people, in principle, it should be possible to isolate a human memory and activate it at will, scientists said.
“We would have every reason to expect this would happen in humans exactly as it happened in mice,” said Michael Kahana, director of the University of Pennsylvania’s Computational Memory Lab, who was not involved in the study.
Researchers said the ability to implant a false memory was a scientific milestone; Kahana called it a “technical tour de force.” The study’s authors said this type of research could one day help treat some emotional problems, such as post-traumatic stress disorder, which involves the intrusion of unwanted memories.
The first step in the mouse experiment took place last year when Ramirez and his colleagues isolated an individual memory in a mouse’s brain by tagging the brain cells associated with it, and inducing recall of the memory at will by forcing those neurons to fire with light. In this new study, they artificially stimulated neurons to make associations between events and environments that had no ties in reality, and in essence, implanted a new, false memory.
They used a technique called optogenetics, which uses light to turn on and off activity of individual brain cells in an animal.
In their experiment, the scientists implanted memories associated with certain rooms or chambers where they placed the mouse.
Say a mouse gets put in a chamber with red walls. It is sniffing around when suddenly it feels a mild shock zap its feet. When the mouse is dropped into the same red room the next day, even if there’s no shock, it recalls the unpleasant experience and freezes in fear.
“(After the jolt,) it formed a new memory that this chamber is a very dangerous place,” said senior author and MIT neuroscientist Susumu Tonegawa.
Next, Tonegawa and his colleagues wanted to find out if they could induce recollection of a memory by forcing the neurons associated with that memory to fire. When put in a different, benign blue room, the mouse moves about and probes the new surroundings as usual. But once the scientists force those neurons to activate, the mouse immediately remembers the bad experience and freezes.
“Now that we can reactivate a memory, can we tinker with that memory, maybe making it into a false memory?” asked Ramirez.
Putting a new mouse in the red chamber, researchers let it recognize the room as harmless. The next day, they had it explore a blue-walled chamber, and gave it a mild jolt while simultaneously inducing recall of the red room. This was meant to artificially associate the memory of the shock-free red room with the fear of being shocked.
On the third day, Tonegawa and colleagues placed the mouse in the red room, where it froze even though nothing bad had ever happened to it there. A false memory had been formed and recalled.
Because he finds implanting fear “kind of depressing,” Ramirez next wants to try to implanting pleasurable memories in mice, such as thoughts about rodents of the opposite sex.