July 26, 2013
Scientists Implant False Memories Inside The Minds Of Mice
redOrbit Staff & Wire Reports - Your Universe Online
Researchers exploring the phenomenon of false memory have taken a page out of science fiction, successfully demonstrating that fake recollections could be implanted into the brains of mice.
"According to the Innocence Project, eyewitness testimony played a role in 75 percent of guilty verdicts eventually overturned by DNA testing after people spent years in prison," explained Joel N. Shurkin of Inside Science News Service. "Some prisoners may even have been executed due to false eyewitness testimony."
The witnesses in these cases were not lying, they simply remembered things wrong, according to MIT molecular biologist Susumu Tonegawa. His study revealed that many of the neurological traces of the memories implanted into the rodents' brains were identical to real memories.
"Whether it's a false or genuine memory, the brain's neural mechanism underlying the recall of the memory is the same," Tonegawa, senior author of the paper, said in a statement. Furthermore, he and his colleagues claim that their study provides additional evidence that memories are stored in neuron networks that form memory traces for every experience a person or creature has - a phenomenon they first demonstrated in 2012.
In order to give false memories to mice, the MIT researchers first engineered a benign virus that could infiltrate cells and unload a gene which led to the production of a protein known as channelrhodopsin-2, explained Discovery News writer Jesse Emspak.
Tonegawa and his colleagues had previously determined that channelrhodopsin-2 stimulated cellular activity (specifically, memories, in this case) when it is exposed to light.
The virus was injected into the mouse's hippocampus, or the region of the brain where episodic (day-to-day) memories are formed and stored. That process occurs when slight changes occur to certain brain proteins, and based on their previous work, they knew which specific cells to target with light.
In order to illuminate the cells, the MIT researchers inserted a thread-thin fiber optic cable into the mouse's brain. After that, they put the mouse into a box known as environment A, which they dubbed the "safe" zone. There, they allowed the mouse to move about normally, running and exploring, for approximately 10 minutes. During this process, the mouse reportedly acted fairly calm, Emspak said.
The following day, the mouse was placed in a second box known as environment B. Here, they pulsed light into their brains to reactivate the memory of the first environment, and then they gave the creature mild foot shocks, which mice consider noxious or punishing. When the animals were returned to environment A (the "safe" zone), Tonegawa's team found that they now displayed heightened fear responses.
"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," the Institute explained in a statement. "Moreover, that false memory appeared to compete with a genuine memory of chamber B, the researchers found. These mice also froze when placed in chamber B, but not as much as mice that had received a shock in chamber B without having the chamber A memory activated."
The scientists discovered that immediately after experiencing recall of the implanted memory, the mice experienced elevated neural activity levels in the amygdale, the brain's so-called fear center. The amygdale received memory information from the hippocampus just like when the mice recalled an actual memory, they said. Now, the MIT researchers plan to conduct additional research of how memories can be distorted within the brain.
"Now that we can reactivate and change the contents of memories in the brain, we can begin asking questions that were once the realm of philosophy," said lead author and MIT graduate student Steve Ramirez. "Are there multiple conditions that lead to the formation of false memories? Can false memories for both pleasurable and aversive events be artificially created? What about false memories for more than just contexts - false memories for objects, food or other mice? These are the once seemingly sci-fi questions that can now be experimentally tackled in the lab."