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N°32 I quarterly I January 2014 Insights | 31 Neurosciences American researchers successfully implanted false memories in mice. Neurobiologist Serge Laroche explores the implications of this discovery. Reshaping Memories BY julien bourdet Fiction has become reality. A US team at the Massachusetts Institute of Technology (MIT) has for the first time succeeded in implanting false memories in the brain of mice, which reacted as if they were real. This breakthrough sheds light on how our own memory works and could even lead to deleting unpleasant memories from the human brain. THE EXPERIMENT To achieve this scientific first, the MIT researchers used optogenetics, a technique whereby certain neurons are activated by exposure to a light source. To be receptive to light, the nerve cells must have been previously modified genetically to express a protein called channelrhodopsin. During the experiment, the mice with modified neurons were placed in chamber A, which was new to them. “They memorized this new environment by activating a specific set of neurons, which, as a result, synthesized the channelrhodopsin,” explains CNPS1 researcher Serge Laroche. The next day, the mice were placed in chamber B, which looked different from chamber A. The scientists reactivated the memory of chamber A by lighting up the neurons that had expressed channelrhodopsin using a probe implanted in the animals’ brains. Simultaneously, the mice received a mild electric shock to their paws. On the third day, they were placed once more in chamber A and showed fear, although they had never received an electric shock in that chamber. Laroche explains that “by making the mice relive the memory of chamber A while receiving an electric shock in chamber B, the scientists managed to make them associate two independent events to create a false memory.” TANGIBLE RESULTS This research in mice—an essential animal model for neuroscientists—sheds light on human memorization processes. It clearly supports the hypothesis, which arose in recent years, that our memory is not permanently fixed, but is dynamic and likely to change whenever we remember something. “A memory corresponds to a specific configuration of the activity of interconnected neurons,” explains Laroche. “When we remember something, this neuronal network is not only reactivated, it is also updated: new information—an electric shock in the case of this experiment—is incorporated into this memory. Such ‘updates’ may occasionally create a false memory, as demonstrated by the MIT team.” POTENTIAL CHANGES Without going as far as predicting a science fiction scenario where people’s memories could be manipulated at will, the idea of creating false memories could one day be used as a therapy. “In the future, we hope to be capable of erasing bad memories in patients suffering from post-traumatic stress disorder (PTSD),” suggests Laroche. In these individuals, it is known that events related to the initial trauma (places, people, etc.) can trigger unpleasant memories. The aim would therefore be to eliminate this association, or even create false and pleasant memories related to this context. This approach could also be used to fight drug addiction. “Of course, optogenetics cannot be performed on humans,” the researcher says reassuringly. “Instead, we could use chemical compounds to block the activity of specific neurons. Trials are already underway that might one day lead to treatments.” 01. Centre de neurosciences Paris-Sud (CNRS / Université Paris-Sud). serge laroche Director of the Centre de neurosciences Paris-Sud in Orsay, he studies the cellular and molecular mechanisms involved in memory and its malfunction. Contact information: CNRS, Orsay. Serge Laroche > serge.laroche@u-psud.fr dr © s. mill et for cnrs le journal


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