The GPS that guides our brain
James Mitchell Crow investigates the sophisticated mapping system in the brain that earned the scientists who discovered it a Nobel Prize.
These days you could parachute into Timbuktu and mosey your way to the best café – as long as you have your smart phone app with the little blue “you are here” dot to guide you. It turns out the brain has its own GPS, with cells that provide the equivalent of that dot. The discovery earned the 2014 Nobel Prize in Physiology or Medicine.
Born in the US, neuroscientist John O’Keefe spent most of his career at University College, London. In the 1970s he discovered cells that record place with pinpoint precision. O’Keefe used electrical probes to monitor rats’ brains as they wandered a walled environment and noticed electrical activity in the hippocampus – the part we now know to be associated with spatial memory. These neurons, which he named “place cells”, seemed to be tracking the rat’s position. One place cell would always fire an electrical signal when the rat was in the northwest corner of the cage, another would fire near the eastern wall, and so on across the environment.
Deep in a rat’s brain, it seems, there’s the equivalent of a little blue dot telling the animal where it is on a mental map of its world.
How does the brain construct these mental maps? That’s the question O’Keefe’s fellow Nobel winners, Norwegian husband and wife research team May-Britt and Edvard Moser, set out to answer – initially as researchers in O’Keefe’s London lab in the mid-1990s, and then as independent researchers at the Norwegian University of Science and Technology in Trondheim. While studying a part of the brain neighbouring the hippocampus called the entorhinal cortex they discovered it was packed with cells they dubbed “grid cells”.
Whereas each place cell recorded the position of a single point in the rat cage, individual grid cells fire at multiple positions. The cells project a grid-like pattern, across the rat’s mental map – just like the lines of latitude and longitude on Google Maps. But rather than the pattern of square gridlines, grid cells use hexagons, projecting a honeycomb-like pattern. Whenever the rat’s path took it across a corner of one of these hexagons, the cell would fire.
Neighbouring grid cells, the Mosers found, project similar honeycomb patterns so that every point in the environment is covered. Wherever the rat stood, there was a grid cell telling the animal where it was.
Place and grid cells work together to provide the rat’s GPS. Place cells seem driven by visual information, the position of boundaries such as corners and walls in the environment seem very important to their function. Grid cells, on the other hand, track motion.
“If you close your eyes and walk around your bedroom, you’ve got a pretty good idea of where you are,” says Caswell Barry, a researcher in the same UCL department as O’Keefe. “Updating your position based on your motion, rather than what you can see or feel around you, is what grid cells seem to do.”
The more we examine human brains, the more it seems we map our world in the same way rodents do – but with certain embellishments. Human brains are richly annotated with events that have happened to us at certain landmarks, and the people we shared these moments with. For instance, most people can recall exactly where they were when they learned about the events of September 11, 2001.
Perhaps, as O’Keefe was the first to propose, that’s because our sophisticated memory is built upon the basic spatial recall that first evolved in smaller brains, like the rat’s.