Yesterday, three scientists were awarded the Nobel Prize in Physiology or Medicine for their discovery of two types of brain cells involved in keeping track of where we are when moving around. Called place cells and grid cells, they may hold the key to understanding aspects of neurological diseases such as Alzheimer's. Laura Colgin, who did research with two of the prize-winning scientists awarded this year’s Nobel Prize, is now an associate professor of neuroscience in the University of Texas at Austin’s College of Natural Sciences who continues to investigate the role of place cells in spacial memory tasks and more.
According to Ila Fiete, also an associate professor in the department, the discovery of these types of cells is a big deal in neuroscience. They shed light on higher cognitive functions in the brain, showing how the brain works with information not directly related to sensory inputs or motor commands.
The cells’ discovery has unmasked large mysteries, namely, how these cells function and why they exist.
Imagine you’re in a pitch-black hotel room at night, and you want to make it from the bed to the bathroom without bumping into various obstacles and without turning on the light. Chances are, even with little in the way of sight, sounds and smells to go on, you can do it pretty well. But your brain has to do some pretty heavy processing of a wide range of information from your muscles, joints and inner ear to accurately estimate where you should be and that means there are many opportunities for errors to creep in. Neuroscientists, therefore, assume the brain must have some way to reduce noise in order to have any hope of getting it right.
A remarkable feature of grid cells provides a possible clue about how the brain does this error correction. When an animal, say a rat, moves around inside a square box looking for bits of food (following a path like the gray line in the left image), an individual grid cell in its brain will fire anytime the rat is on one of perhaps dozens of spots on the floor of the box, forming a hexagonal grid pattern (red dots in the right image). Another nearby grid cell also fires in a hexagonal grid pattern, but one that is slightly shifted over on the floor of the box.
Fiete and her colleagues have shown that grid cells—with their remarkable patterns of activation that precisely tile the space like a crystal lattice as mammals move around -- can encode information in a special way that allows the brain to perform computations. The brain also is able to reject noise, in much the same way that the data in a CD is encoded to ensure that the player can read it even when it is scratched. Their work also explains how an ever-increasing set of possible locations (imagine walking through Central Park for the first time) can be represented in the brain without requiring an equally rapidly increasing number of brain cells.
If the scientists are correct, this would be the first example of an "exponentially scaling code" found in the brain. It also could be the answer to how we can keep track of large amounts of information, including where we are, without succumbing to corruption of that information by noise and without requiring vastly more neurons than we already have.
Fiete and others are now conducting experiments and analyzing the activity of grid cells to determine how the circuit is set up and how it might arise through learning.
“To me what’s really exciting about grid cells,” says Fiete, “is that there may be a whole class of coding schemes in the brain that we didn’t realize existed before."
Updated on Oct. 15, 2014.
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