Scientists implant false memories into brains of mice

Scientists found they could reactivate a false recollection at will by manipulating the light pulses to part of the brain where it was stored

PUBLISHED : Saturday, 27 July, 2013, 12:00am
UPDATED : Saturday, 27 July, 2013, 3:17am


Scientists have implanted a false memory in the brains of mice, hoping the experiment will shed light on the well-documented phenomenon whereby people "remember" events or experiences that have never happened.

False memories are a major problem with witness statements in courts of law. Defendants have often been convicted of offences based on witness testimony, only to have their convictions later overturned when DNA or other evidence is brought to bear.

Our experiments provide the first animal model in which false and genuine memories can be investigated at the memory engram level

The latest advances in studying manipulated memories in the laboratory were reported in the Science journal by US and Japanese researchers at the Massachusetts Institute of Technology.

According to lead author Susumu Tonegawa of MIT, the method involves recognising the brain cells that are changed physically and chemically during the formation of a memory, known as an engram.

"Whether it's a false or genuine memory, the brain's neural mechanism underlying the recall of the memory is the same," said Tonegawa, a 1987 Nobel laureate and director of the RIKEN-MIT Centre for Neural Circuit Genetics. "Our experiments provide the first animal model in which false and genuine memories can be investigated at the memory engram level."

Tonegawa and colleagues showed they could identify the cells for a specific memory in the hippocampus (a part of the brain central to memory-making) of mice and programme the engram to respond to pulses of light, known as optogenetics.

Researchers placed the mice in a peaceful place, Box A, and isolated the animals' brain response to that secure setting. Then, they placed the mice in Box B and reactivated the secure memory while delivering a shock to the mice's feet.

When researchers returned the mice to Box A, the mice froze with fear, signifying they remembered something bad happening there, even though it had not.

Scientists found they could reactivate the false memory at will by manipulating the light pulses to the part of the brain where the memory was stored.

They could also see the false memory stimulated other parts of the brain, such as the amygdala, where active fear responses are based. "To the animal, the false memory seems to have felt like a real memory," said co-author Xu Liu.

Learning how to turn on false memories may also help scientists figure out how to temporarily turn off - or even permanently erase - bad memories, he added.

According to Bill Klemm, senior professor of neuroscience at Texas A&M University, the research could help treat conditions like post-traumatic stress.

"False memory is a big deal. It comes up in criminal trials and post-traumatic stress syndrome, all sorts of things. This paper is important in that here is an animal model where you can do things you can't do in people," said Klemm who did not take part in the study.

However, the study offers only a first glance at how these processes may work in humans, since the lives of lab mice are much less complicated, and the memory span studied was short, he added.

"There was only a one-day interval in between each condition," said Klemm.

"In a real world situation, such as eyewitnesses at a crime, days or weeks or months may elapse between the different contexts and a lot of intervening things may happen."

Elizabeth Loftus, a distinguished professor of psychology at the University of California-Irvine, said she found the research "kind of exciting" because it appeared to answer a key question raised by critics.

"When you work with humans you do have a concern about what we in psychology call demand characteristics - the idea that humans are giving you the response they think you would like to hear," she said. "That is probably not true for mice."

Besides, not all false memories are harmful. Loftus said this flexibility allowed humans to self-correct after misremembering something, and even helps us plan for the future.

"Even without external influence, people remember that their grades were better than they were, or that they voted in elections that they didn't vote in, or that their kids walked and talked at an earlier age than they really did," she said.

"These self-enhancing memory distortions allow people to feel better about themselves."

MIT researchers said they were planning more study of how false memories were created, and whether they could extend to memories for objects, food, or even companions.

Agence France-Presse, The Guardian