One of the long-standing mysteries of neuroscience is the brain's ability to remain flexible enough to learn new things while simultaneously retaining existing knowledge. To better understand this mechanism, researchers studied neural interactions along pathways connecting the hippocampus and neocortex. Particular attention was paid to the CA3 and CA1 regions of the hippocampus and their connections with the retrosplenial cortex, an area involved in navigation and spatial memory retrieval.
The CA3 region transmits rapid and continuous streams of information. The study showed that most of these incoming signals converge on a small group of CA1 neurons—about a quarter of their total number. These same neurons then process and transmit the information to the retrosplenial cortex, but with a completely different activity pattern. This creates an independent outgoing communication channel. This dual functionality allows neurons to multiplex incoming and outgoing signals without mixing them.
This is similar to the way a telephone switchboard handles multiple connections simultaneously without allowing lines to cross. This allows new memories to be integrated into existing neural networks without disrupting previously stored information.
Furthermore, these same neurons remain active during sleep. They are involved in so-called sharp wave oscillations—processes considered important for memory consolidation. Researchers suggest that maintaining the activity of the same set of cells day and night helps transfer new information from the hippocampus to long-term storage in the cerebral cortex.
To conduct the experiments, the scientists trained six mice to navigate a special track with a reward at both ends. Using high-density electrodes, they simultaneously recorded the activity of hundreds of neurons and correlated each burst of activity with the animals' behavior. Later, similar observations were conducted during sleep, allowing them to trace the reproduction of daytime patterns of brain activity.
The authors believe the discovery may have implications not only for the study of Alzheimer's disease and other memory disorders, but also for the development of artificial intelligence. Modern AI systems often face the problem of "forgetting," where learning new tasks leads to the loss of previously acquired knowledge. The "memory switch" mechanism discovered in the mammalian brain may suggest new approaches to creating algorithms capable of continuous learning without overwriting previously acquired information.
