The inner GPS of the brain
The 2014 Nobel Prize for Physiology and Medicine was shared between UCL Professor John O’Keefe and May-Britt and Edvard Moser from the Norwegian University of Science and Technology for their work on nerve-cells that tell us where we are.
In the mid-20th century Edward Tolman watched rats moving around in labyrinths and suggested that the brain might contain a ‘cognitive map’, allowing animals to learn to navigate and find their way.
In 1971, John O’Keefe found the first key to the inner GPS in our brain: place cells. He recorded nerve activity in the hippocampus of the brain in freely moving rats. He found single cells that only activated when the rat was in a certain position in the environment. Different places cells were active for different positions, creating an inner map in the brain telling the animal where it is in the environment. The visual input but also all the other sensory cues were used to create a map. The hippocampus can generate numerous maps, represented by the collective activity of the place cells that are activated in the different environments. Therefore the memory of the environment can be stored as a specific combination of place cell activities in the hippocampus.
Nearly 30 years later, in 2005, May Britt and Edvard Moser watched rats but looked at cells in the Entorhinal cortex of rat brains, a region close and very well connected to the hippocampus. Here, they found nerve-cells weren’t active in only one location but fired when the rats passed multiple locations. Each of these cells was activated in a unique spatial pattern and collectively these “grid cells” constitute a coordinate system that allows for spatial navigation, a system arranged in a hexagonal grid. This coordinate system divides the environment into latitudes and longitudes that basically keeps track of how far we are from a turning and/or starting point.
Together, the information from grid cells, from other cells recognizing the direction of the head and the borders of the room in the entorhinal cortex, and from place cells in the hippocampus, form a comprehensive circuitry for a positioning system, a kind of inner GPS in the brain. This nerve cell network has since been found in rodents, bats, monkey and humans and is now thought to be found in all mammals.