The Brain Never Stops Making Maps

There is still much we have to learn about the functioning of our brains. Although we have been able to pinpoint what some areas of our brains do, there are still many aspects of our brains that we don’t understand. Not only are researchers working on the functioning of the human brain, but studies on other animals can also lead to breakthroughs.

One specific area of research that has scientists interested is the study of the brain’s grid cells. By studying rats, researchers can begin to understand how brains are able to create mental maps.

Grid cells are specialized nerve cells that help with orientation. Without active grid cells, we would get lost (more easily than some of us already do!) and become disoriented, unable to remember even the places we are very familiar with.

Researchers studying grid cells in rats have shown that they remain active, even during periods of time when the rats are sleeping. Two preliminary studies that focused on grid cell activity in rats have shed new light on what researchers call the brain’s ‘inner GPS’ system.

These mapmaking cells are located in the medial entorhinal cortex of the brain. Grid cells were discovered in 2014 by one of the teams that later published one of the most recent studies on grid cells. Researchers were looking to see what happens to grid cells when their host doesn’t need their particular mapmaking knowledge anymore. By studying grid cell activity during sleep, researchers could begin to decipher just how important they are. They could also start to understand grid cell behavior when rats are exploring new and familiar environments as well as sleeping.

Measurements of medial entorhinal cortex activity across awake state of navigation (RUN), slow-wave sleep (SWS), and rapid eye movement sleep (REM). Source: Gardner et. al., 2017).

Measurements of medial entorhinal cortex activity across awake state of navigation (RUN), slow-wave sleep (SWS), and rapid eye movement sleep (REM). Source: Gardner et. al., 2017).

Grid cells in rats give off regular signals to the rat’s brain. These signals mark different locations as the rat moves around. Individual grid cells work together and create what we would call a mental map of the rat’s surroundings. The more a rat goes across the same territory, the more familiar that place seems because of the grid cell’s signals.

Grid cells continue to work together when rats are asleep. By studying pairs of grid cells while rats were awake and again while they were asleep, the two research teams found that the grid cells behaved the same across both scenarios. Active exploration didn’t affect how the grid cells signalled the rats, nor did sleep slow down those signals like you would expect.

The studies showed that a pair of grid cells fired nearly in tandem with one another while the rat was awake, and continued to fire in the same pattern during sleep. The rat’s internal map was left intact because the grid cells didn’t change their behavior. If the grid cells stopped working or slowed down during sleep, researchers think that our mental maps wouldn’t be as durable.

Since grid cells have only been discovered recently, there is still much to be learned about them. By studying rats, researchers can get insight into how grid cells behave the same or differently than they do in humans.


The Studies

Gardner, R. J., Lu, L., Wernle, T., Moser, M. B., & Moser, E. I. (2017). Correlation structure of grid cells is preserved during sleep. bioRxiv, 198499.

Trettel, S. G., Trimper, J. B., Hwaun, E., Fiete, I. R., & Colgin, L. L. (2017). Grid cell co-activity patterns during sleep reflect spatial overlap of grid fields during active behaviors. bioRxiv, 198671.

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