The brain's coordinate system
At the Kavli Institute for Systems Neuroscience in Trondheim, researchers located a fundamental component of our ability to navigate. In 2005, May-Britt and Edvard Moser identified a new type of neuron they called a "grid cell". The discovery came from experiments recording brain activity in rats as they moved around an open area. The scientists observed that certain cells in the entorhinal cortex fired in a unique and astonishingly regular pattern.
Instead of firing in just one location, each grid cell became active at multiple points. When mapped, these firing locations formed a perfect hexagonal grid that tessellated across the entire environment. Collectively, these neurons generate a coordinate system that the brain uses for pathfinding and understanding its position in space. Grid cells have since been found in numerous mammals, including mice, bats, monkeys, and humans. The system is modular, with different sets of grid cells creating grids of varying scales, from fine-grained to coarse.
From place to prize
The discovery of grid cells built upon earlier work from 1971 by John O'Keefe, who found "place cells" in the hippocampus. Place cells are neurons that fire only when an animal is in one specific location in an environment. O'Keefe concluded these cells form an internal map of a room or area. The question that remained for decades was how the brain knew where the animal was, in order to activate the correct place cell.
The Mosers' discovery of grid cells provided the answer. Grid cells in the entorhinal cortex provide the universal coordinate system, the metric for space; place cells in the hippocampus use that input to associate a specific location with memories and events. Together, these two cell types form the brain's positioning system. This breakthrough earned O'Keefe, May-Britt Moser, and Edvard Moser the 2014 Nobel Prize in Physiology or Medicine. Their combined work solved a problem that had occupied scientists for centuries: how the brain creates a map of its surroundings. Research into this system also has clinical implications, as the entorhinal cortex is one of the first areas affected in Alzheimer's disease, which could explain the spatial disorientation common in patients.