Washington - Stressful events can often coincide with the creation of false memories, when people recall things that never happened, and scientists said on Thursday they are learning more about this curious phenomenon.
A better understanding of false memories could help treat post-traumatic stress and possibly cut back on inaccurate eyewitness testimony that jails innocent people, experts say.
The latest advances in studying manipulated memories in the lab were reported in the US journal Science by researchers in a US-Japanese partnership at the Massachusetts Institute of Technology.
They say they can make mice remember a traumatic event that never happened.
According to lead author Susumu Tonegawa of MIT, the method involves recognizing 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," explained 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 of mice and program the engram to respond to pulses of light.
Researchers placed the mice in a peaceful place, Box A, and isolated the animals' brain signature of 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.
False feels like real
When researchers returned the mice to Box A, they froze, exhibiting a common fear response, even though nothing bad was happening.
Scientists also observed they could reactivate the false memory at will by manipulating the light pulses to the part of the brain where the memory was stored.
Even more, they could see the false memory aroused 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 turn off, or erase, bad ones, he added.
According to Bill Klemm, senior professor of neuroscience at Texas A&M University, the research could help treat conditions that affect humans, 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 the sense in that here is an animal model where you can do things you can't do in people," said Klemm, who was not involved in the research.
However, the study may offer only a preliminary 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 limited, he added.
"One thing that needs to be pointed out, is that this is relatively short-term memory. There was only a one-day interval in between each condition," Klemm told AFP.
"In a real world situation, like eyewitnesses at a crime or something, days or weeks or months may elapse between the different contexts and a lot of intervening things may happen that were prevented from happening in this controlled laboratory environment."
According to co-author Steve Ramirez at MIT, the findings will further research on how memories are distorted, and what conditions lead to the formation of a false memory.
"Can false memories for both pleasurable and aversive events be artificially created?" asked Ramirez.
"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."