When the mice were put in a third chamber unlike the first two and were not given the light flash, they were unafraid. They were not reminded of their previous experiences, real or imagined.
The scientists had planted a false memory, and the mice believed it.
Tonegawa said people who remember falsely are not lying; they completely believe what they say. People with false memories are among those who can beat polygraph machines. Even when confronted by facts, such as DNA evidence, they refuse to believe their memories are wrong.
Elizabeth Loftus a cognitive psychologist at the University of California, Irvine, who has done more than almost anyone in attacking false and implanted memories in courtrooms and who has appeared as an expert witness in many trials, including the McMartin trial, said the finding was “very exciting.”
“It converges well with human data showing you can plant emotional memories into people’s minds,” she said.
Tonegawa, who won the Nobel Prize for Physiology in 1987, said there is a bright side to all this. Only humans have false memories; animals do not unless, like the mice at MIT, false memories are forced on them, he said.
“Humans are the most amazing, imaginative animals,” he said. “We are thinking. Lots of things are going on. Humans are recording what happens and passing it on.”
An imperfect memory, Tonegawa said, may be the price we pay for the imagination and creativity that makes us human.