By analyzing the activity of “GPS” neurons in mice, researchers at the Stanford University School of Medicine have discovered that the mental maps created by these cells accumulate errors, which are corrected when the animal encounters a wall.

The findings support the theory that these cells, called grid cells, use an animal’s perceived speed and direction to help it navigate familiar places.

Thus, as you stumble through your pitch-black kitchen in the middle of the night for a glass of water, your body knows how many steps to take and when to turn to get to the sink. Scientists believe grid cells are responsible for constructing the internal, GPS-like map that keeps you from colliding with the refrigerator.

But grid cells can make small errors, the Stanford researchers assert, taking you to the dishwasher instead of the sink, at which point other nearby neurons, called border cells, assist in reorienting the grid cells to correctly map your current position.

How the brain integrates this sensory and motion data is one of the big open questions of spatial navigation. A paper that helps to answer that question was published April 16 in Neuron. Lisa Giocomo, PhD, assistant professor of neurobiology at Stanford, is the senior author; the lead author is graduate student Kiah Hardcastle. This work was done in close collaboration with the theory lab of Surya Ganguli, PhD, assistant professor of applied physics at Stanford, who is the other co-author on the study.

Learning from Nobel laureates

A decade ago, grid cells were identified in the entorhinal cortex of the brain by Norwegian scientists May-Britt Moser, PhD, and Edvard Moser, PhD, who were among the winners of last year’s Nobel Prize for the discovery of the neurons involved in self-location and navigation. They found individual cells that fired consistently when a mouse wandered past certain places in both light and dark enclosures. At each of these places, a unique set of grid cells activated, presumably signaling to cells in the hippocampus the mouse’s location.