False memory implanted in mice

False memory implanted in mice

In an article entitled, ‘Creating a False Memory in the Hippocampus’ published in July 26, 2013, issue of Science (Vol. 341 no. 6144 pp. 387-391 ), the lead author Steve Ramirez with seven other associates affiliated to RIKEN-MIT Center for Neural Circuit Genetics at the Picower Institute for Learning and Memory & Howard Hughes Medical Institute, MIT have implanted a false memory in the brains of mice and they hope that will shed light on the well-documented phenomenon whereby people remember events or experiences that have never happened. 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 the authors, both false and genuine memories seem to rely on the same brain mechanisms. The 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, the team firstly introduced a mouse to a chamber that it had never seen before and allowed it to explore the sights and smells: a black floor, dim red light, and the scent of acetic acid. The next day, the mouse found itself in a decidedly more unpleasant chamber: The lights, colors, and smells were all different, and it received a series of mild electric shocks to its feet. While the mouse was getting shocked, the scientists used optical fibers implanted in its brain to shine pulses of blue light on its dentate gyrus (part of the hippocampal formation), reactivating specific cells that had been labeled the day before as the mouse explored the first, less painful chamber. The hope was that the mouse would form a new (and totally false) association between the first room and the painful shocks. Even though the mouse never got shocked in the red-and-black, acid-scented room, it froze in fear when it returned there, confirming that it had formed a false, context-specific memory. However, it is impossible to know just what the mouse experienced as the scientists stimulated its brain with light—whether it felt some or all of those earlier sensations, or even perceived that it was back in the first chamber during the shocks. But it is clear that the rodent recalled a painful experience when it returned to that first environment. It showed no signs of fear when placed in a third, unfamiliar chamber, demonstrating that the fear response was indeed triggered by the first room. The team hopes that these results could help explain some of the cases in which humans form false memories. [summarized by Samsad Research Associate at Plant Biotech lab, DU.]

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