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Inside your brain, grid cells function as spatial rulers, helping you create mental maps of the world around you. In a new Nature Communications publication, assistant professor of bioengineering Holger Dannenberg, together with postdoctoral researchers Blanca Gutiérrez-Guzmán and J Jesús Hernández-Pérez ask: If the world suddenly gets bigger, do our mental maps stretch with it, or do they break?
Grid cells, neurons in the medial entorhinal cortex that fire in precise, hexagonal patterns as animals move through space, were discovered decades ago. “The hypothesis was that this grid pattern essentially provides a metric for navigation in space,” Dannenberg explained. “It was considered to be a universal map, preconfigured before we even start navigating the world.”
To test that assumption, the research team recorded neuron activity in freely moving mice as they explored environments that changed in size. Using microelectrodes, the team tracked how grid cells behaved as walls were pushed outward. When the environment expanded modestly, grid cells behaved as expected. Their firing patterns scaled linearly to accommodate the larger space, Dannenberg explained. But when the expansion crossed a critical threshold, the hexagonal pattern collapsed. “At some point, those grid maps completely get disrupted,” he said. Crucially, the mice did not stop navigating in the expanded environment; only the presumed universal metric failed.
This finding directly challenges the idea that grid cells provide an all‑purpose spatial ruler. Instead, navigation appears to rely on a system with built‑in limits, one that must learn when those limits are exceeded.
Grid cells are organized into discrete modules, each operating at a characteristic spatial scale that increases as a step function. A group of small grid cells, which are best suited to mapping small environments, like a single room, may be next to a group of medium-sized grid cells, which help map medium-sized places, like a building. Dannenberg’s team found grid maps remain stable as long as environmental changes stay within the scale ratio between neighboring modules. Once that ratio is exceeded (i.e., once a room becomes the size of a building), adaptation fails.
When an environment expands beyond the system’s built-in limit, the small grid cells cannot easily map it; they need extra time to reconfigure a new mental map.
Learning does occur. After two to three weeks of exposure to the enlarged arena, grid patterns gradually re‑emerged. “It takes time, and it’s a learned process,” Dannenberg said.
Even then, the recovered grid pattern did not scale up. The small grid cells that mapped the room wouldn’t become medium-sized grid cells when the room became the size of a building. Rather, the mental map of the expanded space would be mapped with the granularity of a small space. “You’re not adapting to the largest scale,” Dannenberg said. “You’re learning how to apply the same spatial resolution to a larger space.”
Beyond navigation, Dannenberg’s work has broader implications for memory and disease. The entorhinal cortex is affected early in Alzheimer’s, and grid‑like activity is linked to episodic memory, the brain’s ability to place events in space and time. By mapping the structures that map the world, Dannenberg’s research helps explain not only how we find our way, but also how we may lose it when those maps begin to fail.