Locating the GPS system in the brain
PhD student David Weston reports on his top stories for the month....
David - The second paper this week marks a significant milestone for brain navigation research. A group of scientists at Princeton University have been working towards locating the human GPS system, an area of the brain that is responsible for allowing us to successfully navigate our environment.
David Tank and his team focused on the medial entorhinal cortex, an area of the brain that has previously been associated with the way in which we map physical space.
Within the entorhinal cortex we find neurons called grid cells that fire electrical signals at particular places within the space. Remarkably these grid cells form a pattern of activation that looks like the hexagonal spaces on a Chinese Checkers board. So a single grid cell will fire when you occupy specific hexagons within a room for example.
Now two competing theories have predicted how these grid cells electrically encode the physical landscape. The first, the so-called oscillatory interference model, proposes that individuals grid cells produce oscillations in their electrical activity that inform you of where you are, while the competing attractor model suggests that the ramping electrical patterns of grid cells, communicating with one another, are responsible for the positional information.
The authors decided to test which of these theories is most valid by taking electrical recordings from the entorhinal cortices of mice navigating a virtual-reality environment. Although they found that both the oscillations and ramps were present in these cells, the ramping electrical activity much more reliably predicted the positional information, giving support to the attractor model.
These important findings have come some way into understanding how the complex patterns of electrical activity in the brain co-ordinate to give us reliable and accurate information about the ways in which we can interact with our world.