Scientists have successfully implanted false memories of an event that never happened into a brain as part of a study showing how easy it is to create inaccurate recollections of what happened in the past.
The study is based on research into the memories of laboratory mice but the scientists believe it could also explain false-memory syndrome in humans, such as cases where people honestly believe that something has happened even when they are told it did not.
False memory syndrome is important in court cases that rely on the veracity of eye-witness accounts, which can be notoriously unreliable. Almost three quarters of the first 250 convicted criminals in the United States who were exonerated as a result of new DNA evidence, for instance, were originally convicted on the basis of eye-witness testimony.
“False memory in humans often results from mixing different sources of information or confusing something thought or imagined with reality,” said Xu Liu of the Massachusetts Institute of Technology in Cambridge, Massachusetts, who was part of the research team.
“In our study we brought back an old memory in the mouse brain and artificially associated it with a real stimulus, thus we generated a new memory for an event that never happened in reality. This illustrated one possible way how false memory can form in humans,” Dr Liu said.
“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,” Dr Liu added.
“It might be hard to imagine that mice have memories, but like other biological traits, memory is essential to life and thus is conserved throughout the animal kingdom, from sea slug, fruit flies, to mice and human,” he said.
The study, published in the journal Science, used specially-bred mice with a photosensitive pigment in their brains that stimulates the recovery of a genuine memory when the animals are exposed to a certain kind of light stimulus.
This has allowed the researchers to study nerve connections in the “memory cells” of a part of the mouse brain called the hippocampus. Pulses of light could be used to bring back a genuine memory as well as a false memory created by associating a true memory with the memory of a small but unpleasant electric shock.
Using this approach, the scientists were able to implant the false memory of being in a box where the mice were given electric shocks even when this did not actually happen, the scientists said.
They also found that the neural connections made during the formation of a genuine memory were practically identical to those made during the formation of a false memory – suggesting a physical basis for false-memory syndrome.
“We found that a false memory interacts with a true memory just like a regular memory. Also, the false memories activated the same region as true memories,” Dr Liu said.
“Interestingly, sometimes people are more confident about false memories than true ones. Without outside references, a false memory is as real as a true memory to us,” he said.
Although a pain stimulus was used in the experiment to stimulate the formation of a false memory in the mice about a fearful situation, the scientists believe other stimuli, such as a particular smell or taste could be used to implant and recover a false memory in the human brain.
“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, director of the RIKEN-MIT Centre for Neural Circuit Genetics in Saitama, Japan, who led the study.
“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,” Professor Tonegawa said.
The precedent: Alan Alda and the eggs
Trying to implant false memories into the minds of people is difficult, but not impossible. One of the most famous cases was the American actor Alan Alda who was making a science documentary about the work of Elizabeth Loftus, a psychologist at the University of Washington in Seattle.
During a picnic lunch on a university campus Alda was offered a hard-boiled egg, which he refused on the grounds that he had made himself sick as a child by eating too many boiled eggs.
It turned out that Ms Loftus had managed to implant this false memory during a previous questionnaire session when she had revealed some “facts” to Alda about his childhood, which included being sick on eggs. She also managed to convince another experiment volunteer that he had got lost in a shopping mall as a child and was “found” by an elderly gentleman who led him back to his mother. Convinced of his false memory, the man even came up with a detailed description of the elderly man who had found him. He also rated this false memory as more real even than some of his genuine childhood memories.
Ms Loftus has also managed to convince people that on a previous trip to Disneyland they had had an encounter with the cartoon character Bugs Bunny, even though this would have been impossible given that the buck-toothed rabbit is owned by the rival Warner Brothers film studio.