Throughout our experiences in life, our brain picks up things to remember along the way and helps us take past experiences to aid interpretation of encounters in the present. At the same time, there are several occasions where we come across different and new things that we have to learn and adapt to for the first time. Scientists from the Institut Pasteur have now identified a neural signal in the hippocampus, the brain region responsible for memory, that informs the brain on when to switch gears between a learning and memory state.
“How the brain finds the balance between these two opposing processes is a question that has fascinated neuroscientists for a long time,” says Christoph Schmidt-Hieber, head of the institute’s Neural Circuits for Spatial Navigation and Memory Laboratory.
Schmidt-Hieber and team set out to address this gap in knowledge, designing an experiment where mice explore virtual reality (VR) environments while their brains are recorded. “We realized that the main obstacle to studying how the brain reacts to novelty was physical reality itself!” explains Ruy Gómez-Ocádiz, a PhD student in the laboratory and first author of the study.
Researchers say it would be nearly impossible to study the effect that new exposure has on the brain with a more traditional neurology study method. That’s because it would be difficult to keep track of everything that changes according to each mouse’s perception.
So the authors generated a video game simulation for the rodents to create the VR scenario. As the mice followed the rules of the games, they were rewarded with sugar treats. As they played, the team tracked neuronal activity in the hippocampal region in real-time. They identified an electric signal in the region that activates exactly as the mice switch virtual worlds. This means that their brains are triggered upon unfamiliarity, and the signal prompts a conversion from memory to learning mode.
Teaming up with French physicists, the team then developed a computational model based on their initial findings. The model would address the question of whether new exposure and the subsequent signaling mechanisms could work as a switch that allows the brain to swap back and forth between memory and learning based on specific information in the environment initiating the signal.
Future work will continue to test and build on this, and the scientists are excited to see where research goes from here. “The discovery of this novelty signal in the hippocampus provides exciting new clues to understand how the brain finds the necessary equilibrium between formation of new memories and recall of familiar ones,” concludes Christoph Schmidt-Hieber.
This study is published in the journal Nature Communications.