Your brain may have brief windows when it is primed to transform a passing moment into a lasting memory.
Researchers at the University of Tübingen found that natural shifts in alertness can briefly change the hippocampus, making its memory circuits more receptive to new information. The findings suggest that memory formation depends not only on what happens to us but also on the brain’s condition at that exact moment.
The study, published in Nature Communications, was led by Professor Andrea Burgalossi of the Institute of Neurobiology and the Werner Reichardt Center for Integrative Neuroscience (CIN).
The team focused on the hippocampus, a brain region that helps create episodic memories of particular places and events. In both mice and humans, the hippocampus contains place cells, neurons that become active in specific locations and help build an internal representation of the surrounding world.
“In laboratory settings, we can expose mice to different environments and observe how the place cells become active,” says Dr. Eduardo Blanco-Hernandez of the University of Tübingen, one of the lead authors of the study. “Different groups of place cells represent different environments. Watching their activity is like observing memories being formed or reactivated in real time.”
Alertness Reshapes Memory Circuits
While recording these neurons in mice, the researchers also tracked the animals’ level of alertness. The brain does not remain in one steady condition, even during rest. It continuously moves between states of lower and higher arousal that can alter how its networks process information.
“The internal brain state can be estimated from pupil size,” says CIN researcher and co-author of the study, Nicola Sartorato. “When we become more alert or engaged, our pupils dilate. The same is true in mice.”
As the mice became more alert, a particular group of place cells grew more active. These shifts occurred even when the animals were not moving, showing that the changing activity was linked to an internal state rather than a new location or behavior.
“A specific subset of place cells became especially active when the animals became more alert,” explains Nicola, “suggesting that internal state can rapidly reshape the neuronal substrate of episodic memories.”
Brain Rhythms Signal Readiness
The same pattern appeared in theta oscillations, rhythmic waves of neural activity associated with learning, navigation, and memory encoding. Their strength rose and fell alongside changes in alertness, further indicating that the hippocampus repeatedly shifts between different levels of readiness.
The researchers suspected that these brief periods might represent windows of heightened plasticity, when neural circuits are especially capable of changing. Plasticity allows neurons to strengthen, weaken, or reorganize their connections, creating the physical changes that preserve an experience.
“Plasticity is essential for memory because it is the process by which the brain physically stores experiences,” says Professor Burgalossi.
This flexibility is particularly important for episodic memory. Unlike a fact that can be studied repeatedly, many personal experiences happen only once and may last only seconds. The brain must therefore capture and organize the information immediately.
“This is especially important for episodic memory, since the events we experience in life happen only once. There is no repetition, no rehearsal—so the brain must capture and store them quickly and efficiently in real time,” says Burgalossi.
Creating New Memory Cells
To test whether heightened alertness made the hippocampus easier to reshape, the researchers stimulated individual memory-related neurons during those periods. Neurons that had not previously responded to particular locations began developing location-specific activity, effectively becoming new place cells. The result suggests that even limited stimulation, when delivered at the right moment, can recruit new “memory cells” into the hippocampal network.
The results portray memory formation as a process that is constantly opening and closing. The hippocampus does not appear equally prepared to store information at all times. Instead, it enters short periods when its circuitry becomes unusually responsive and easier to reconfigure.
“What’s exciting is that we can now study these processes in a controlled way, by focusing on moments when the brain is naturally more plastic,” Burgalossi says.
Reference: “Place and behavioral modulation of hippocampal neurons during immobility” by Nicola Sartorato, Ioannis S. Zouridis, Ulzii-Utas Narantsatsralt, Eduardo Blanco-Hernández and Andrea Burgalossi, 24 July 2026, Nature Communications.
DOI: 10.1038/s41467-026-75492-w
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