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How Steph Curry is Like a Bat

Bats, too, keep track of their teammates’ locations.

Last night, Stephen Curry of the Golden State Warriors finished the regular basketball season with 402 three-pointers, far eclipsing anyone else. He is also one of the best in the NBA at assists, including no-look passes.

At the International Congress of Neuroethology two weeks ago in Montevideo, Uruguay, David Omer of the Weizmann Institute of Science in Israel opened his presentation with a video clip in which Steph Curry, dribbling toward the basket, makes a precise pass to a teammate several feet directly behind him. How does Curry do this?

We may not be able to find out what’s going on in Curry’s brain, but it turns out that bats do something similar.

Bats don't play basketball. But many bats do live and fly in groups and they do keep track of other bats, even when they can't see them. (And yes, bats can see, although many species are better at hearing.) Omer, along with Nachum Ulanovsky and Liora Las, trained Egyptian fruit bats to remain still while keeping track of the flight path of another bat, even when the other bat moves out of their field of view. When bats do this, nerve cells (neurons) in their brain can be monitored via tiny electrodes that transmit the neuron’s signals wirelessly.

Yossi Yovel, used with permission
Egyptian fruit bats
Source: Yossi Yovel, used with permission

Using this set-up, they found that there are nerve cells in a part of the bat’s brain (the hippocampus) that signal (by firing action potentials, or spikes) whenever the other bat is in a particular location. Different neurons fire for different locations in space, so collectively, this group of neurons keeps track of where the other bat is.

In another talk from the Ulanovsky lab at the same meeting, Arseny Finkelstein described how bats also keep track of their own location in space and the direction in which they are moving. Individual neurons in the hippocampus fire spikes rapidly when the bat is in a particular location in a room (a different location for each neuron). In another part of the bat’s brain, neurons instead fire rapidly when the bat is moving in a particular direction. All these neurons collectively keep track of the bat’s place and heading in the world.

Neurons like these had previously been described in rodents, earning John O’Keefe, May-Britt Moser, and Edvard Moser the 2014 Nobel Prize in Physiology or Medicine. But the bat research goes beyond the rodent research by showing that these neurons keep track of space and direction in 3 dimensions.

Of course, bats are not known for their vision. They are better known for using echolocation, the animal version of sonar, to navigate and to catch insects in the dark. Many bats make very high-frequency sounds (ultrasound, too high-pitched for humans to hear) and listen carefully to the timing and frequency of the echoes. The bats that do this are the smaller species that hunt insects, not the large bats that eat fruit and nectar.

(Click here to download an animation of an actual chase between a bat and two insects, from Cynthia Moss and Annemarie Surlykke.) Bats can be incredibly precise using echolocation, as James Simmons of Brown University showed—for example, they can discriminate a change in distance about as small as the diameter of a cell!

How do they do this? Essentially, their brains do math, as demonstrated by research largely in Nobuo Suga’s lab at Washington University in St. Louis, focusing on mustached bats.

Mustached bat
Source: Alex Borisenko, Biodiversity Institute of Ontario/Wikimedia [CC BY-SA 3.0]

The time it takes for the sound they make to echo back to their ears (divided by 2, because the sound has to reach the insect and then return to the bat) multiplied by the speed of sound equals the distance of the insect. Individual neurons in their brains (first in the midbrain and later in the cerebral cortex) fire spikes rapidly only for a particular object distance, by responding selectively to the combination of a pulse sound followed by an echo sound, with a particular delay between them. Neurons that are next-door neighbors in the brain fire most for similar pulse-echo delays, forming a map of object distances in the brain.

In a different part of the brain, neurons fire spikes fastest for particular differences in frequency between the pulse and echo. The echo frequency is higher when a bat flies toward an insect, due to the Doppler effect.

The Doppler effect is what happens to the sound of an ambulance’s siren or a train’s whistle: as it moves toward you, the sound frequency or pitch increases (because the sound waves are compressed) and as it moves away from you, the frequency decreases (because the sound waves are stretched). The frequency-comparing neurons allow the bat to know how quickly it is approaching the insect (its relative velocity).

Together, the distance-tuned and velocity-tuned neurons in the bat's brain allow the bat to track down and scoop up hundreds or thousands of insects in the dark every night, a feat perhaps on a par with Steph Curry’s basketball skills.