“If mice had Hollywood, this would be ‘Inception’ for them,” said one of the lead researchers, MIT neuroscientist Steve Ramirez, whose 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 hadn’t.

… 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 a living animal. An optical fiber feeds light into the mouse’s hippocampus, the area of the brain that plays a prominent role in forming new memories…

Because he finds implanting fear “kind of depressing,” Ramirez next wants to try to implant pleasurable memories in mice, such as thoughts about rodents of the opposite sex.