Inside the brain's GPS system

     May-Britt Moser, Edvard Moser, and John O’Keefe were just awarded the 2014 Nobel Peace Prize in Physiology or Medicine for their work with grid cells.  May-Britt and Edvard are a married couple with a lab at Norwegian University of Science and Technology in Trondheim.  Their area is figuring out how the brain functions and learning more about the neural code for cognition.  Their mentor John O’Keefe is known for discovering place cells in the hippocampus of rats in the 1970’s.  The hippocampus functions in memory formation, spatial organization, emotional responses, and long-term potentiation.  Place cells are activated when a rat is in a particular location.  It is believed that humans use a similar system to know where they are in relation to their surroundings.

     The Moser’s goal was to better describe the source of the place cell’s signal.  They study this by putting electrodes directly on a rat’s hippocampus and recording the signals as the rats run around a box.  The electrodes are sensitive enough to pick up the activity of a single neuron.  Then, a computer plots the location when each neuron fires.  To tell exactly where the place cells were working they chemically inactivated parts of the hippocampus and observed where the cells still functioned normally.

     What they found is that input to the place cells comes from the entorhinal cortex.  This cortex is located just inferior to the hippocampus (Figure 1).  From the data they noticed a pattern emerge of where the neurons were firing, a “near perfect hexagon lattice appeared”.  This was huge; no one could have imagined a pattern better than this.  It is so mathematically based and a very effective, optimal system, allowing for high resolution with minimal grid cells used.  They also found that smaller hexagonal-grids were located higher in the entorhinal cortex, while larger grids were forming lower in that cortex.  There is still much to learn in this area, we don’t know the process in which grid patterns are formed by the entorhinal cortex or how this enables animals to move from one place to another. 

 

Figure 1. http://www.lookfordiagnosis.com/mesh_info.php?term=Entorhinal+Cortex&lang=1

     The Mosers have plans to address these issues in upcoming experiments.  Their lab wants to have rats run on a stationary ball and show them images of changing environments, while their heads are held in place so electrodes can be placed on individual cells connected to a lense to microscopically observe the cells in real time.  They would also like to investigate when this grid system develops in the rat’s life.

     Grid cells are not the first discovery in the entorhinal cortex, it is also known for its role in memory.  It is one of the first areas to be affected by Alzheimer’s disease.  One of Alzheimers patient’s first symptoms is getting lost, or not finding their way home.  It would be groundbreaking if some special characteristics of these grid cells were allowing the disease to develop there first.  I believe this is strong evidence that the Mosers and team are on to something with their work in grid cells and how humans form maps inside their brain, like a GPS. 

Scientific American, How the 2014 Nobel Prize Winners Found the Brain’s Own GPS

http://www.scientificamerican.com/article/how-the-2014-nobel-prize-winners-found-the-brain-s-own-gps/

(The article also has a cool video towards the bottom to visualize the experiments.)

This is a link to the Moser’s and others published paper in 2005 about this topic (abstract only):

http://www.nature.com/nature/journal/v436/n7052/full/nature03721.html