Scientists discover how hippocampal CA1 memory switchboard safeguards past knowledge

Brain Reuses Cells to Store and Retrieve Different Memories

Neuroscientists at NYU Langone Health have identified a neural mechanism that explains how the brain learns new information while preserving existing memories1

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. Published in Nature on May 13, the study reveals that approximately one in four memory cells in the hippocampal CA1 region functions as a shared hub that connects incoming and outgoing signals without mixing them up2

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. This memory switchboard prevents new memories from overwriting old ones by changing how the same cells fire together rather than activating entirely new neurons.

How Hub Neurons Route Signals Through Divergent Firing Patterns

The research team focused on a neural chain linking the cornus ammonis 3 (CA3), which sends fast-changing information, to the hippocampal CA1, and finally to the retrosplenial cortex, which handles navigation and long-term storage1

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. Using high-density electrodes, investigators conducted multi-region recording across hundreds of individual neurons in six mice trained to run on a rewarded track. They discovered that a minority of CA1 cells carry most incoming messages from CA3, then fire in a completely different pattern when transmitting signals to the retrosplenial cortex2

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. "Our findings help explain how memory can be both moldable and enduring," said study co-lead author Joaquín Gonzalez, PhD, a postdoctoral fellow in the Department of Psychiatry at NYU Grossman School of Medicine2

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. This separation of incoming and outgoing channels allows the retrosplenial cortex to maintain stability while other regions continue learning from experience.

Memory Consolidation During Sleep Strengthens Past Knowledge

The critical hub neurons remain active during sleep, replaying waking patterns inside brain events known as sharp-wave ripples1

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. Because the same core of cells handles both daytime processing and nighttime replay, the pathway from hippocampus to cortex stays open to solidify memories2

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. "Our study shows how learning and memory consolidation can coexist in the same network," said study co-lead author Mihály Vöröslakos, MD, PhD, a postdoctoral fellow in NYU Grossman School of Medicine's neuroscience department2

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. This discovery was enabled by recording hundreds of individual neurons across all key regions simultaneously in animals moving naturally.

Implications for Neurological Disorders and Catastrophic Forgetting in AI

Co-senior author Dr. Zhe S. Chen noted that this memory switchboard may provide clues about circuit failures in Alzheimer's and other neurological disorders that affect the brain's ability to recall events2

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. The findings also offer a biological blueprint for addressing catastrophic forgetting in AI networks, which tend to erase prior learning when trained on new tasks1

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. "By showing how the mammalian brain can safeguard memories during learning, our research may offer a biological blueprint for designing next-generation AI technology that can update itself continuously without overwriting what it has already acquired," said co-senior author György Buzsáki, MD, PhD, the Biggs Professor of Neuroscience at NYU Grossman School of Medicine2

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. The research team plans to examine whether similar switchboard-like channels appear in other memory circuits.