Scientists from MIT have planted a false memory in multiple mice , and found neurological traces of the memories showing that they’re 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,” said Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and senior author of a paper describing the findings, in a statement.
Episodic memories, or memories of experiences, are made of several elements, including objects, space, and time. The associations of these elements are hardwired into chemical and physical changes in neurons, or electrically excitable cells.
The memory traces, also called engrams, remain somewhat mysterious and scientists have been trying to find out where they reside in the brain.
In a study last year, the researchers conditioned the brains of a set of mice to fear a particular chamber by shocking them, and the memory was formed. The cells encoding the memory trace was “labeled” with light-sensitive proteins. The mice were put in a normal chamber and behaved normally but reacted with fear when the researchers delivered a pulse of light to the hippocampus area of the brain.
“Compared to most studies that treat the brain as a black box while trying to access it from the outside in, this is like we are trying to study the brain from the inside out,” Liu says. “The technology we developed for this study allows us to fine-dissect and even potentially tinker with the memory process by directly controlling the brain cells.”
In the new study, the researchers worked on using reactivated memory traces to see if they could implant false memories in the mice’s brains.
“First, the researchers placed the mice in a novel chamber, A, but did not deliver any shocks,” according to the study description from MIT. “As the mice explored this chamber, their memory cells were labeled with channelrhodopsin. The next day, the mice were placed in a second, very different chamber, B. After a while, the mice were given a mild foot shock. At the same instant, the researchers used light to activate the cells encoding the memory of chamber A.
“On the third day, the mice were placed back into chamber A, where they now froze in fear, even though they had never been shocked there. A false memory had been incepted: The mice feared the memory of chamber A because when the shock was given in chamber B, they were reliving the memory of being in chamber A.”
Howard Eichenbaum, a professor of psychology and director of Boston University’s Center for Memory and Brain, who was not part of the study, said the research shows a lot of progress in memory research.
“They identified a neural network associated with experience in an environment, attached a fear association with it, then reactivated the network to show that it supports memory expression,” he said. “That, to me, shows for the first time a true functional engram.”
The MIT team is planning further studies in the field.
