Scientists from Japan and the United States have shown that they can plant false memories in the brains of genetically modified mice.
The team identified cells, shown in red, in the mouse hippocampus where memory traces are stored (Steve Ramirez / Xu Liu)
Their study, published in the journal Science, may lead to new understanding of how and why humans form false memories. It also shows that many of the neurological traces of these memories are identical in nature to those of authentic memories.
“Whether it’s a false or genuine memory, the brain’s neural mechanism underlying the recall of the memory is the same,” explained senior author Prof Susumu Tonegawa from the MIT’s Howard Hughes Medical Institute.
The study also provides further evidence that memories are stored in networks of neurons that form memory traces for each experience we have.
Neuroscientists have long sought the location of these memory traces, also called engrams. In previous studies, Prof Tonegawa and his colleagues showed that they could identify the cells that make up part of an engram for a specific memory and reactivate it using a technology called optogenetics.
Now, they successfully implanted a false memory into mice by manipulating engram-bearing cells in the hippocampus, a seahorse-shaped part of the brain known to play a role in forming and storing memories of experiences.
They zeroed in on the animals’ brain cells that represented the safe environment of a setting, Box A, and programmed those cells to respond to pulses of light. They then placed the animals in a completely different environment, Box B, and pulsed light into their brains to reactivate the memory of Box A. They gave the animals mild foot shocks, creating a negative association between the light-reactivated memory of Box A and the foot shocks, which mice find highly aversive. When the animals were placed back in Box A, the researchers found that the animals now displayed heightened fear responses.
“Humans are highly imaginative animals. Just like our mice, an aversive or appetitive event could be associated with a past experience one may happen to have in mind at that moment, hence a false memory is formed,” Prof Tonegawa said.
“These kinds of experiments show us just how reconstructive the process of memory actually is,” said lead author Steve Ramirez, a graduate student at MIT.
He said that memory is not a carbon copy, but rather a reconstruction, of the world we’ve experienced. “Our hope is that, by proposing a neural explanation for how false memories may be generated, down the line we can use this kind of knowledge to inform, say, a courtroom about just how unreliable things like eyewitness testimony can actually be.”
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Bibliographic information: Steve Ramirez et al. 2013. Creating a False Memory in the Hippocampus. Science, vol. 341, no. 6144, pp. 387-391; doi: 10.1126/science.1239073
