Egyptian fruit bat. (Seregraff/Getty Images)

Bat Brain Study Reveals How Animals Use 'Place Cells' to Navigate in Space And Time

CONOR FEEHLY
16 JULY 2021

You're running down the road and all of a sudden a car pulls out in front of you. In a split second your brain projects your location and predicts you will collide with the car., telling your muscles to engage in an evading maneuver. In this moment, your brain is paying more attention to where you will be rather than where you are. 

 

This ability to project our current location into the future is a key characteristic of the mammalian navigational system, and can often mean the difference between life and death. 

To further understand this phenomenon, neuroscientists have peered into the minds of fruit bats as they flew around a room with cameras tracking their movements, and feeders to encourage them to fly, at speeds of up to 50 kilometres per hour (31 mph). 

Researchers compared the wirelessly tracked neural activity of Egyptian fruit bats (Rousettus aegyptiacus) with their flight paths and noticed that the bats' 'place cells' - unique neurons responsible for encoding an animal's spatial position - were more closely correlated with where the bats would be in the near future, rather than where they were at that specific moment in time. 

"We wanted to find out: Does the neural activity at the present moment do a better job at representing a past or future position than it does the actual present position? And we found that, for some neurons, neural activity actually does a much better job of representing a future position," said study lead author and neuroscientist Nicholas Dotson from UC Berkeley. 

 

Place cells are a type of neuron located in the hippocampus; they become active when an animal moves into particular locations in its environment. Different locations are represented by different place cells, which form a sort of internal neural 'map' of the surrounding space. 

"If you had access to neural activity in my hippocampus while I walked around a room, you'd be able to decode where I was in the room based on this neural activity," Dotson said.

Previous research has revealed how these dedicated neurons code for spatial positions in rodents, finding that their place cells encoded for positions immediately in front of the animals, rather than farther along the path. Researchers believed this was due to their slower movements in experimental environments. 

Bats, on the other hand, fly around at tremendously high speeds, which requires them to plan and rapidly predict positions further into the future, causing their positional representations to extend out along a continuum of space and time.

In this study, the bats' neural activity correlated with their spatial position much more strongly when their position was projected a few hundred milliseconds, or a second into the future. 

Place cells have been identified in a wide variety of mammals, however it is not clear yet if this ability to project up to a second in the future is unique to bats and their high-speed movements. The brains of slower animals, including humans, simply may not need to plan that far ahead.

"Terrestrial creatures may not need to project as far into the future as a bat, but, even for humans, it could vary by situation. If you're walking, you are probably content with knowing what's going to happen just ahead of you. But when you're driving, you want to know what's going to happen three meters or more away from you, because you're moving at a very high speed," says neurobiologist Michael Yartsev, also from UC Berkeley.

"Now that we know that there is some neural representation of future position in bats, we can go and ask: What are the shared components between different animals? And in what ways, and to what extent, do humans exhibit this ability?"

The study was published in the journal Science.