For a decade, scientists have been puzzled by how the “internal maps” of the human brain are anchored to the external world. A new study published in the journal Nature attempted to solve this puzzle.

Share on Pinterest The orange lines in this illustration depict forces acting on the internal map to produce a final grid geometry that is asymmetric to the environment.

Image credit: Tor Stensola/Kavli Institute for Systems Neuroscience

The scientists behind the new study – from the Norwegian University of Science and Technology in Trondheim, Norway – compared the brain’s internal map to how we might use a map and compass to relate longitude lines to the terrain around us while hiking.

Nobel Laureates Edvard Moser and May-Britt Moser had previously discovered “grid cells” in the brain that are the main reference in our brain’s spatial navigation system. These cells allow internal grid maps to be “pulled up” as appropriate to guide us in the right direction. The new study helps to explain how these maps are anchored to our surroundings.

The Norwegian team recorded the activity of grid cells in rats as the animals hunted for cookie crumbs around a 1.5 m2 box.

“We recorded the activity of hundreds of grid cells,” says Tor Stensola, a researcher at the Kavli Institute for Systems Neuroscience in Norway.

“Looking at the information from more than 800 grid cells, we noticed that grid patterns typically were oriented in the same few directions,” Stensola explains. “This was true for all the animals studied, which suggested the grid map aligns to its surroundings in a systematic way. Grid cells all seemed to be anchored to one of the local walls, but always with a specific offset of a few degrees. So we decided to investigate this.”

As a way of visualizing this, the researchers explain that if a map represented by the activity of grid cells were to represent the box, it would need to look and be aligned the same every time the rat was in the box.

Analyzing data from recordings of the grid cells’ activity in the rats’ brains, the team found that these recorded maps were consistent and that each grid pattern was linked to one of the walls of the box. However, the axes of the grids were not perfectly aligned – they were askew. The angle was always approximately 7.5 degrees off.

Stensola did some calculations and realized there might be a good reason for that particular angle: