2014’s Nobel Prize for Physiology or Medicine has been awarded to John O’Keefe, May-Britt Moser, and Edvard Moser for their discovery of the brain’s “inner GPS” system. The prize revolves around their discovery of place cells and grid cells — special neurons in the hippocampus and entorhinal cortex of animals (including humans, monkeys, and rats) that appear to create a cognitive map of every room or space that you’ve ever explored. As you move around a room or space, a very specific place cell fires — and when you visit the same place again in the future, the same place cell fires every time. The three researchers will share a $1.1 million prize.
Back in 1971, O’Keefe and Jonathan Dostrovsky discovered that the rat hippocampus had special place cells that, as their name suggests, are specifically involved with the rat’s current place. Prior to 1971 we already knew that the hippocampus was deeply involved with memory and learning, but the specificity of place cells and the cognitive spatial map they constructed was groundbreaking work. Later work has shown that there really are specific pyramidal neurons that fire in a certain pattern when an animal (rat, human, etc.) is in a specific place.
Then, in 2005, the two Mosers found that the entorhinal cortex — a region of the brain that feeds into the hippocampus — went one step further and actually has a region of grid cells: pyramidal neurons that are arranged in an almost perfect triangular grid (pictured below). These grid cells are effectively a coordinate system, with a specific spatial location triggering a specific firing of grid cells. The grid does not correlate directly with the physical world, though; if you take a step to the left, the grid cell to the left doesn’t necessarily fire. Rather, it seems the brain uses some kind of special encoding method to make sense of the grid connections.
Recent research has shown that grid cells, along with other neurons in the entorhinal cortex, form a network with place cells in the hippocampus (pictured top). In the words of the Nobel Committee for Physiology or Medicine, “This circuitry constitutes a comprehensive positioning system, an inner GPS, in the brain.” Most research into grid and place cells has revolved around rats, but early work suggests the human brain does things in much the same way.
The three scientists are being awarded a Nobel Prize because the discovery of an internal positioning system is, “a paradigm shift in our understanding of how ensembles of specialized cells work together to execute higher cognitive functions.” This paradigm shift, combined with our rapidly improving ability to image and analyze brain activity, means we’re on the cusp of understanding how the human brain does other high-level tasks, such as planning and thinking.