Memories are notoriously unreliable–from sometimes garbled childhood recollections to more grave instances involving misidentification of a criminal perpetrator. Now, researchers have demonstrated that erroneous memories can be physically implanted in a mouse’s brain, causing it to mis-remember where an unpleasant experience occurred. The new study could provide scientists with a better understanding of how false memories are created in humans.
Reporting Thursday in the journal Science, lead author Xu Liu of the Riken-MIT Center for Neural Circuit Genetics at Massachusetts Institute of Technology (MIT) said the team was able to cause mice to remember receiving an electric shock in one location when the shock actually was administered in a completely different one. To accomplish this, the scientists placed mice in one environment long enough for them to form memories about it. Then, they identified and chemically labelled the creatures’ brain cells where the memories were arising.
Later, the mice were moved to a different environment and given an electric shock while the researchers stimulated their brain cells with light to trigger the earlier memories. When the mice were returned to the first environment, they reacted with fear, showing that they “remembered” being shocked there, even though it never happened. According to Liu and colleagues, they performed a number of variations on their experiment to confirm their findings. They say their data demonstrates the possibility of generating “an internally represented and behaviorally expressed fear memory via artificial means.”
The team used a technique known as optogenetics to locate and label the mice neurons and make them sensitive to activation by blue light transmitted by optic fibers, which delivered pulses of light to the animals’ brains. Optogenetics, a revolutionary approach to neuroscience, combines optics and genetics to control and measure the activity of individual neurons in living tissue.
Although a mouse brain is much simpler than the human brain, its basic structure and chemistry is similar. Consequently, studying how neurons work in a mouse’s brain could shed light on how similar components work in the human brain.
“In the English language there are only 26 letters, but the combinations of letters make unlimited words and sentences,” Liu told BBC News. “This is also true for memories.”
Liu explained that because so many brain cells are involved in the creation of a memory, different combinations of small numbers of brain cells can give rise to a specific recollection when they are activated. These varying combinations of cells could be the reason that memories evolve rather than remaining static like a photo frozen forever in time. That is why we are able to incorporate new information into old memories and how erroneous memory can form without our knowing it, Liu said.
Neil Burgess from the University College London, who did not participate in the study, told BBC News that the findings are impressive, saying they could lead to a better understanding of why people have fearful associations and the eventual ability to reduce or eliminate the strong negative emotions experienced by people with post-traumatic stress disorder.