A study led by Spanish researchers has shed light on how the brain stores new experiences without erasing or confusing memories that already exist. The findings point to a flexible role for a region of the hippocampus, offering fresh insight into memory formation and recall.
Scientists from the Institute of Neurosciences, jointly run by the Spanish National Research Council (CSIC) and Miguel Hernández University, examined how inhibitory neurons in the dentate gyrus respond when new information is added. Their research was published in PLOS Biology and involved experiments in mice supported by computational modelling.
How the brain separates overlapping memories
Everyday experiences often unfold in stages. A person may remember a building before renovation, the construction work itself and the completed result. Although these events are connected, the brain generally needs to keep them distinct so that one memory does not overwrite another.
The new research suggests that the dentate gyrus helps manage this challenge. This section of the hippocampus is involved in generating memories and distinguishing between experiences that share similar features.
Within the dentate gyrus, inhibitory neurons reduce the activity of other cells. Rather than simply switching memory formation on or off, this process appears to help the brain select how strongly it should preserve an existing memory and how readily it should encode incoming information.
Experiments in mice
The research team altered the level of inhibition in the brains of mice and then assessed how the animals retrieved information. When inhibition was reduced, the mice showed behaviour associated with stronger retrieval and more detailed recollection under some experimental conditions.
Encarni Marcos, co-lead author of the study and head of the relevant research line at the Institute of Neurosciences, said the results did not indicate that one level of inhibition is always superior. Instead, the effect depended on how much information the brain had to process.
Memory does not use one fixed setting
The computational model developed for the research provided an important qualification. Lower inhibitory activity appeared helpful when the memory load was relatively light. However, that advantage did not continue when the amount of new information became substantially larger.
This suggests that the hippocampus may adjust its operating mode according to the circumstances. When a new experience is important and sufficiently distinct, the dentate gyrus may support the incorporation of new information. When incoming stimuli risk interfering with an established memory, the same system may help stabilise what has already been learned.
The researchers describe this as a dynamic mechanism shaped by context and task demands. In practical terms, the brain may balance two competing requirements:
- Encoding new experiences: allowing fresh information to be recorded as a separate memory.
- Protecting existing memories: preventing new and similar events from becoming confused.
- Adjusting to memory load: changing the balance as the volume and complexity of information increase.
Why the findings matter
Memory research often focuses on how information is stored, but the ability to keep similar experiences apart is equally important. Without that separation, people could struggle to identify when or where an event happened, or confuse earlier versions of an experience with later ones.
The study does not establish a direct treatment for memory disorders, and the experiments were conducted in mice rather than people. Nevertheless, understanding how inhibitory circuits regulate memory could contribute to future research into conditions involving memory loss, interference or inaccurate recall.
The work also highlights that memory is not a static archive. The hippocampus appears to continually balance preservation and change, responding to the significance of an event and the quantity of information arriving at the same time.
What remains to be studied
Further research will be needed to determine how closely the mechanism observed in mice corresponds to human memory. Scientists may also investigate whether changes in inhibitory activity are linked to ageing, neurological disease or differences in learning environments.
Because the findings point to a context-dependent process, future studies could examine how emotion, attention and the similarity between events influence the dentate gyrus. These factors may help explain why some experiences remain sharply separated in memory while others become blended.
Conclusion
The Spanish study suggests that the brain protects existing memories and incorporates new information through a constantly adjusted balance of inhibition in the hippocampus. Rather than relying on one ideal setting, the dentate gyrus appears to adapt according to the memory load and the demands of the task. The finding offers a clearer picture of how the brain preserves the past while continuing to learn.
