The human brain has a remarkable capacity to transform experiences into lasting memories, allowing us to learn from the past and apply that knowledge to navigate new situations. However, this memory system cannot simply be a static archive of bygone events. Rather, it must be a dynamic process, constantly evolving and adapting to changing circumstances in order to better equip us to predict the future and make sound decisions.

Pioneering research led by Professor Flavio Donato’s team at the Biozentrum, University of Basel, has shed light on the sophisticated mechanisms underlying this dynamic memory storage. Using mouse models, the researchers have discovered that a single memory is not simply recorded as a singular trace, but is encoded in parallel across at least three distinct groups of neurons within the hippocampus, a brain region critical for learning from experience.

The earliest-born neurons are responsible for the long-term persistence of a memory. Although their initial memory trace may be too weak for the brain to readily access, it grows stronger over time. Interestingly, this suggests that in humans, the brain may only gain full access to certain memories some time after they are first encoded.

Parallel memory traces encoded in hippocampal subpopulations defined by development support the dynamics of memory
Parallel memory traces encoded in hippocampal subpopulations defined by development support the dynamics of memory. Credit: Vilde A. Kveim et al.

In contrast, the memory trace created by the latest-born neurons is initially quite robust but then gradually fades, eventually becoming inaccessible to the brain. Nestled between these two extremes are neurons that emerge at intermediate stages of development, encoding a more stable memory copy.

Crucially, the specific memory trace that the brain chooses to activate appears to have profound implications for how that memory can be modified or leveraged to generate new knowledge. Memories stored by the recently-born neurons are more malleable, allowing the brain to readily integrate new information and update the original recollection. Conversely, accessing memories held by the earliest-born neurons is less conducive to such dynamic revisions, as the associated trace has become more rigid over time.

The dynamic way memories are stored in the brain is a testament to the remarkable plasticity of the organ, which underpins its incredible mnemonic capabilities, explains lead author Vilde Kveim.

Flavio Donato’s team has thus demonstrated that the activation of specific memory traces and the precise timing of their retrieval can significantly shape how we remember, modify, and utilize our accumulated experiences. The brain faces a delicate balancing act with memory,” Donato observes. “On one hand, it must maintain a record of the past to help us make sense of the world. On the other, it needs to adapt those memories to the changes unfolding around us, so that we can make informed decisions about the future.

The researchers hope that by further unraveling the mechanisms driving memory encoding and modification in the brain, they may one day find ways to selectively smooth over intrusive, pathological recollections or even recover memories that had been thought permanently lost. The dynamic nature of human memory, it seems, is both a remarkable feat of neurological engineering and a potential avenue for therapeutic intervention.

SOURCES

University of Basel

Vilde A. Kveim et al., Divergent recruitment of developmentally defined neuronal ensembles supports memory dynamics. Science 385, eadk0997(2024). DOI:10.1126/science.adk0997

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