Place cells in the brain are cells that recognize very specific places and are found in an area behind the temple called the hippocampus. While these cells must be sent information from nearby cells to do their job, so far no one has been able to determine exactly what kind of nerve cells, or neurons, work with place cells to craft the code they create for each location. Neurons come in many different types with specialized functions. Some respond to edges and borders, others to specific locations, others act like a compass and react to which way you turn your head.
Now, researchers at the Kavli Institute for Systems Neuroscience at the Norwegian University of Science and Technology have combined a range of advanced techniques that enable them to identify which neurons communicate with each other at different times in the rat brain, and in doing so, create the animal's sense of location. Their findings are published in the 5 April issue of Science.
"A rat's brain is the size of a grape. Inside there are about fifty million neurons that are connected together at a staggering 450 billion places (roughly)," explains Professor Edvard Moser, director of the Kavli Institute. "Inside this grape-sized brain are areas on each side that are smaller than a grape seed, where we know that memory and the sense of location reside. This is also where we find the neurons that respond to specific places, the place cells. But from which cells do these place cells get information?"
The problem is, of course, that researchers cannot simply cut open the rat brain to see which cells have had contact. That would be the equivalent of taking a giant pile of cooked spaghetti, chopping it into little pieces, and then trying to figure out how the various spaghetti strands were tangled together before the pile was cut up.A job like this requires the use of a completely different set of neural tools, which is where the "light switches" come into play.
Neurons share many similarities with electric cables when they send signals to each other. They send an electric current in one direction – from the "body" of the neuron and down a long arm, called the axon, which goes to other nerve cells. Place cells thus get their small electric signals from a whole series of such arms.