Uncovering the Secrets Of Our Internal GPS
There’s a lot of work that goes into navigating through our world, and our brains take on much of the heavy lifting. The brain is full of cell types that are specifically designed to help us decipher our position in space and detect features of our surrounding environment. Two of these cell types are called place cells and grid cells.
Place cells are located in a brain structure called the hippocampus. As we move around, different place cells become active to create an “internal map” of our environment.
Grid cells are located in a part of the brain called the medial entorhinal cortex (MEC), and they activate when we reach a certain point in our environment. They also send information along to the hippocampus, perhaps communicating to place cells the amount of distance we’ve travelled or stimulating their formation.
Grid cells are arranged in a hexagonal grid that tiles the MEC, with cell clusters making up the vertices of each hexagon. The space between these vertices gets larger as you move toward the back of the MEC, expanding the size of the grid—referred to as “grid scale”.
There is little known about how this expansion in grid scale affects place cells or spatial navigation in general. It’s hard to study grid cells because it’s difficult to manipulate them without affecting the surrounding cells that carry out other functions in spatial navigation.
In a recent study published in Nature Neuroscience, researchers from Stanford University including NYSCF — Robertson Investigator Lisa Giocomo, PhD, found a way to selectively manipulate grid cells by knocking out a gene called HCN1 in the MEC of mice. This caused grid scale to expand without affecting surrounding cells, allowing the researchers to then observed changes in place cells and the mouse’s ability to navigate through its environment.
What they found was that increasing grid scale increases place scale—the size of the field in which a place cell will fire. The researchers also found that increasing grid scale impaired the mouse’s ability to navigate to a goal location that moved each day (a skill called “place stability”).
These findings indicate that changes in grid scale do impact place cells, and that expanding the grid scale past its normal boundaries causes issues in spatial navigation and memory, likely by affecting place maps. Future research will further address the relationship between these two cell types.