Scientists have implanted a false memory in the brains of mice in an experiment that they hope will shed light on the well-documented phenomenon whereby people “remember” events or experiences that never happened.
False memories are a major problem with witness statements in courts of law. Defendants have often been convicted of offenses based on eyewitness testimony, only to have their convictions later overturned when DNA or some other corroborating evidence is brought to bear.
To study how these false memories might form in the human brain, Massachusetts Institute of Technology (MIT) neuroscientist Susumu Tonagawa and his team encoded memories in the brains of mice by manipulating individual neurons. He described the results of the study in the latest edition of the journal Science.
Memories of experiences we have had are made from several elements, including records of objects, space and time. These records, called engrams, are encoded in physical and chemical changes in brain cells and the connections between them.
Tonagawa said both false and genuine memories seem to rely on the same brain mechanisms.
In their work, Tonagawa’s team used a technique known as optogenetics, which allows the fine control of individual brain cells. They engineered brain cells in the mouse’s hippocampus — a part of the brain known to be involved in forming memories — to express the gene for a protein called channelrhodopsin. When cells that contain channelrhodopsin are exposed to blue light, they are activated. The researchers also modified the hippocampus cells so that the protein would be produced in whichever brain cells the mouse was using to encode its memory engrams.
In the experiment, Tonagawa’s team placed the mice in a chamber and allowed them to explore it. As they did so, relevant memory-encoding brain cells were producing the channelrhodopsin protein. The next day, the same mice were placed in a second chamber and given a small electric shock, to encode a fear response. At the same time, the researchers shone light into the mouse brains to activate their memories of the first chamber. That way, the mice learned to associate fear of the electric shock with the memory of the first chamber.
In the final part of the experiment, the team placed the mice back in the first chamber. The mice froze, demonstrating a typical fear response, even though they had never been shocked while in that chamber.
“We call this ‘incepting,’ or implanting false memories a mouse brain,” Tonagawa told Science.
A similar process may occur when powerful false memories are created in humans.
“Humans are very imaginative animals,” Tonagawa said. “Independent of what is happening around you in the outside world, humans constantly have internal activity in the brain. So, just like our mouse, it is quite possible we can associate what we happen to have in our mind with bad or good high-variance online events. In other words, there could be a false association of what you have in your mind rather than what is happening to you.”
“Our study showed that the false memory and the genuine memory are based on very similar, almost identical, brain mechanisms. It is difficult for the false memory bearer to distinguish between them. We hope our future findings along this line will further alert legislatures and legal experts how unreliable memory can be,” he added.