Unaided by modern technology, our very survival would depend upon our brain’s ability to accurately map external space. Returning home or to a safe haven, for example, requires that we identify our location in space, remember the way back, and navigate there. For over a century, scientists have asked how the brain represents and remembers our external environment. Only in the last few decades, however, have researchers discovered the basic building blocks of an internal, neural navigation system. This system depends upon neurons in a brain region called the medial entorhinal cortex, which translate the external environment into an internal map of space. In the medial entorhinal cortex, neurons called “grid cells” provide the basis of this internal map of space. A given grid cell increases its activity when an animal or human moves through particular locations in space. For example, if a mouse runs in a straight line, a grid cell will increase its activity every 30 centimeters, relaying to the mouse how far it has run through space. Grid cells, therefore, generate a representation of space similar to a longitude and latitude coordinate system. While originally discovered in rodents, grid cells have now been found in a range of species, from bats to humans, suggesting they are fundamental to how brain remembers location and navigates the animal through space. However, despite the ubiquity of grid cells, how the brain actually creates neurons that respond this way is largely unknown. Our team will address this gap in knowledge by aiming to identify how sensory information can help the spatial maps created by grid cells remain stable over time. Taking an interdisciplinary approach, we will record the electrical activity of neurons in the medial entorhinal cortex of mice while they navigate through space. In addition, we will develop a computational model to investigate the exact way in which these neurons act to generate their external representations of space. Our work will more broadly address how neural activity in the medial entorhinal cortex gives rise to spatial memory and navigation not just in mice, but in other animals, including humans, as well.
Lisa Giocomo, Stanford University
Surya Ganguli, Stanford University