Humans have a built-in neural map, and it’s shaped like a honeycomb.
How did you manage to navigate to the place you are sitting right now as you read this? If you are in a familiar place like your office or favorite café, how did you find your way there? If you are in a new place, how did you explore and navigate the new space? Did you bump along into walls and objects and change course accordingly like an iRobot Roomba vacuum cleaner? Hopefully, not.
So how do we do it? How do we manage a new café with various dimensions, multi-levels, tables, chairs, people, walls, stairs, and other obstacles? We very quickly seem to become cartographers of the environment, using multi-modal sensory information to create some sort of internal, mental map. But is there really a ‘mental map’?
In 1948, Edward Tolman proposed the concept of a ‘cognitive map’. In the late 1950’s, the new technique of implanted micro wires into the brain allowed researchers to study free moving animals. In 1971, using this technique, John O’Keefe found the neural substrate of Tolman’s ‘cognitive map’. When a rat moved into a particular place in an environment, certain cells in the hippocampus (CA1) fired consistently. So when you pass the water station at your local café, certain ‘place cells’ fire in the ‘water place’. However, these ‘water place’ cells are not specifically ‘water place’ cells in all environments, since there may not always be a water place. ‘Place cells’ can be active in different places and environments. They readjust to new places. O’Keefe referred to this as ‘remapping’. In the image above, you can see grid cells firing on a mental map, which tells your feet where (not) to walk.
Hexagons and honeycombs
Fast forward a few decades to the Moser group, May-Britt and Edvard Moser. They were looking to find where the hippocampus was receiving this place information. They set their sites on the entorhinal cortex, which is very close to the hippocampus. While poking and prodding in the rat brain, a particular firing pattern emerged when the animal was allowed to roam freely. A very specific, grid-like pattern… What kind of configuration do you think this would take? What would be an efficient and encompassing layout to represent a space? Nature has her consistent patterns, and here, deep in the brain, we find one yet again.
Cells that fired consistently were observed at the vertices of equilateral triangles (i.e. the place where two lines of a triangle meet), resulting in a familiar pattern regardless of the direction or path the rat was taking. Those of you who are Euclidean fans or 3D designers already know how useful and fundamental equilateral triangles are for tessellating (i.e. tiling) a surface.
Having trouble visualizing this? The image on the left is an example of a surface tessellated with equilateral triangles.
What do you get when you look at all these vertices? What sort of pattern emerges?
Hexagons. Yes, that’s right. Your spatial grid in your brain is laid out like a bee’s honeycomb. So what makes this bee hive pattern in your brain so interesting? Unlike the place cells that reconfigure and “remap” in new environments to new landmarks (like the Roomba vacuum), grid cells retain their hexagonal layout, regardless of environmental changes. This has led scientists to infer this grid is not derived from the outside world but rather is something intrinsic in an organism, created within the brain. Our “mental/cognitive map” is an actual neural map.
Human mapping systems
This was such a landmark discovery, that in 2014 John O’Keefe, May-Britt Moser, and Edvard Moser were awarded the Nobel Prize in Physiology or Medicine. This has now placed place and grid cells on the popular neuroscience research map.
In the past year alone, from the gracious participation of epilepsy patients with depth electrodes implanted in the entorhinal cortex, these grid cells have been observed in humans playing spatial navigation video games. (For those neuroscientists out there, you know how exciting and difficult it is to obtain human data.) The clinical population’s role in these routes of research will be paramount in the coming years, which, in addition to proving information about our neurological mapping systems, will also work towards bridging the gap between laboratory and clinical research.
So now when you get up from your favorite seat at the local café and effortlessly walk home, take a moment to acknowledge and appreciate the sophisticated mental, neural map Nature has endowed you with that your feet effortlessly follow. Follow the map… Beat a new path… Where does it lead? Hopefully to new questions and discoveries.
Bjerknes TL, Moser EI, & Moser MB (2014). Representation of geometric borders in the developing rat. Neuron, 82 (1), 71-8 PMID: 24613417
Langston RF, Ainge JA, Couey JJ, Canto CB, Bjerknes TL, Witter MP, Moser EI, & Moser MB (2010). Development of the spatial representation system in the rat. Science (New York, N.Y.), 328 (5985), 1576-80 PMID: 20558721
O’Keefe J, & Dostrovsky J (1971). The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat. Brain research, 34 (1), 171-5 PMID: 5124915
Solstad T, Boccara CN, Kropff E, Moser MB, & Moser EI (2008). Representation of geometric borders in the entorhinal cortex. Science (New York, N.Y.), 322 (5909), 1865-8 PMID: 19095945
Tolman, E. (1948). Cognitive maps in rats and men. Psychological Review, 55 (4), 189-208 DOI: 10.1037/h0061626