Getting lost in a hall of mirrors is easy: every wall reflects another, and you feel like you've been here before. The brain gets similarly confused when surrounded by many similar places. Neurons responsible for the spatial map can fire the same signal for two different corners of a room. This is called spatial ambiguity.

Usually, the brain relies on boundaries — walls, corners, large objects. But in a symmetric room, boundaries don't help: all corners look alike. Scientists added grid cell signals to the navigation model. These neurons work like an internal coordinate grid: they tile space with a hexagonal lattice, regardless of what the eye sees. The grid overlays the room like an imaginary graph paper, giving each node its own address.

In three environments (an open field, a room with a cross-shaped obstacle, and a maze) adding grid cells reduced ambiguity by 94–99%. The biggest gain was in the most symmetric environment. So grid cells provide the brain with an independent cue: even if the eyes see the same thing, the internal grid tells you where you are.

Thus, the brain doesn't rely solely on external landmarks. The internal coordinate grid helps distinguish two identical halls in a mirror maze, like an invisible floor marking that reflections can't erase.