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Telling the brain when to learn and when to remember; Research by Institut Pasteur

The memory system alternates between periods of learning and remembering

As we go about our lives, our brain continually remembers information that we have learned in the past and uses it to make sense of the world in the present. However, we also often encounter objects and events that we have never experienced before, and then the brain needs to be ready to learn. These two essential functions of our brain’s memory system, learning, and remembering, seem to constantly compete against each other. “How the brain finds the balance between these two opposing processes is a question that has fascinated neuroscientists for a long time,” explains Christoph Schmidt-Hieber, head of the Neural Circuits for Spatial Navigation and Memory Laboratory at the Institut Pasteur.

Using an animal model, scientists from the Institut Pasteur recently identified a neural signal in the hippocampus, a brain region essential for forming and recalling memories, that enables the brain to alternate between remembering and learning modes. The findings were published in the journal Nature Communications on July 15, 2022.

The scientists designed a video game in which mice learn to explore a virtual ‘world’ and get sugar rewards when they correctly follow the rules of a simple game. While mice were engaged in playing the video game, the researchers recorded the activity of neurons in the hippocampus, a brain region that is essential for forming and recalling memories.

Using this innovative approach, they discovered an electric signal in the hippocampus that appears at the precise moment when the animal is teleported to a new virtual world. The signal is emitted by granule cells and triggered by novelty. It induces a transition from a neural state of memory to a state of learning.

Teaming up with physicists from the École normale supérieure, Université PSL, and the CNRS, the scientists then developed a computational model suggesting how such a novelty signal may work as a switch to enable the brain to alternate between remembering and learning modes depending on the information present in the environment. “The discovery of this novelty signal in the hippocampus provides exciting new clues to understand how the brain finds the necessary equilibrium between the formation of new memories and recall of familiar ones,” concludes Christoph Schmidt-Hieber.

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