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 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 eyewitness testimony, only to have their convictions later overturned when DNA or some other corroborating evidence is brought to bear.
In order to study how these false memories might form in the human brain, Susumu Tonagawa, a neuroscientist at the Massachusetts Institute of Technology, 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. According to Tonagawa, 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 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 become activated. The researchers also modified the hippocampus cells so that the channelrhodopsin 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 there. “We call this ‘incepting’ or implanting false memories in a mouse brain,” Tonagawa told Science.