How does our brain understand where our body is in space, and navigate us from home to work? The components of Google Maps are easy for us to discern. We readily understand the mix of GPS location, an extensive map and a sophisticated way-finding algorithm. Our ability to understand our body’s innate relationship to location is far more complex. Discovery of the “inner GPS” of the brain was recently recognized with the 2014 Nobel Prize in Physiology or Medicine, awarded to John O’Keefe, May-Britt Moser and Edvard Moser.
O’Keefe discovered the first component of the brain’s positioning system. He found that a type of nerve cell in the brain’s hippocampus, our short-term memory storage bin, was always activated when a rat was at a certain place in a room. As a rat ran through a maze, a particular sequence of individual neurons fired. Other nerve cells were activated when the rat was positioned elsewhere. O’Keefe concluded that these “place cells” formed a map of the room.
When the rats slept, the same sequences of place cells that were fired earlier in the day fired again. Researchers think that this replay helps to transfer the rat’s memory of the maze from the hippocampus into long-term storage. Place cells also attach to memories of a particular location. When sitting at a table, a person or maybe even a rat might remember a pizza that was eaten at that spot.
Many decades later, the Mosers discovered another component of the brain’s positioning system. They identified “grid cells,” which are thought to act like a dead reckoning system and generate a coordinate system to allow for precise positioning and pathfinding. The grid cells create a location to put place cells and organize position locations. Rats running around an open floor (hopefully not mine), will fire neutrons that map out a grid of equilateral triangles that serve as a spatial map. Grid cells can function in complete darkness, without visual cues. Together, place and grid cells make it possible to determine position and to navigate.
While place and grid cells were first discovered in rats, studies using brain imaging indicate that they also occur in humans. Alzheimer’s patients and those with other neurological diseases are sometimes unable to recognize familiar locales and lose their way. The areas of the brain with the place and grid cells are in the precise area of the brain that is usually affected by Alzheimer’s disease.
With nav apps and access to cell phones, we don’t need to exercise our innate mapping and positioning abilities as much. I wonder if the neurons that were created to help us find our way will suffer from underuse. The opposite seems to be true. A study found that the hippocampi of experienced London taxi drivers were significantly bigger than those of us regular folks. Perhaps a byproduct of Google Maps is a stunted hippocampus. My head feels smaller already.