Egyptian Fruit Bat Brains Reveal How Animals Perceive 3D Space

Bats have some amazing adaptations when it comes to flight. They swoop and soar, darting toward insects or fruit in order to feet at night as they calculate exactly when and how to move. Now, researchers have revealed for the first time how they perceive three-dimensional, volumetric space by measuring bat brain cells during flight.

The new research, which is published in the journal Science, examined how animals orient themselves in three-dimensional settings. Although the question of how mammals orient themselves has been studied in the past, experiments have only been conducted in two-dimensional settings. These older experiments discovered that orientation relies on "place cells," which are neurons located in the hippocampus, the part of the brain involved in memory. Each of these place cells is responsible for a spatial area, and it sends an electrical signal when the animal is located in that area. Together, the cells allow the animal to navigate a whole spatial environment.

Now, scientists have gotten a new look at how these animals navigate--this time, in a three-dimensional environment. The researchers chose to use the Egyptian fruit bat as their subject; it's a very common bat species in Israel, and is relatively large. This allowed the researchers to attach a wireless measuring system to the mammal in a manner that did not restrict the creature's movements.

The wireless system itself is lightweight, only about seven percent of the weight of the bat. It contained electrodes that measured the activity of individual neurons in the bat's brain. This allowed the researchers to study exactly how the bat functioned during flight.

In order to adapt the bat's behavior to their experiment, the scientists adopted a clever solution. Usually, a bat's flight is one-dimensional; the mammal flies straight to a food source in a line. The researchers found that, in the case of a fruit tree, the bats fly around it and utilize the full volume of space surrounding the tree. Therefore, they installed an artificial fruit tree in the laboratory made of metal bars and cups filled with fruit.

After observing the bats, the researchers found that the brain's perception of all three dimensions is uniform. That is, it perceives the three dimensions of space as "equal." However, this may be different for non-flying animals that essentially move in flat space; the different axes might not be perceived at the same resolution.

These findings are of particular interest when it comes to humans, which evolved from apes that moved in a three-dimension space when swinging from branch to branch. Yet now, humans move in a two-dimensional space. The discoveries from this experiment could provide new insights into some basic functions of the brain.