Bats Reveal the Cellular Secret of the '3D Compass'

Despite what some may say, bats aren't blind. Sonar helps, but it isn't everything. Now a new study of the common fruit bat has revealed how exactly these animals keep track of where they are mid-flight - revealing the same mechanism that other mammals and even humans use to guess at location and direction.

Think of it this way. During a road trip, you may have a very good idea of which direction is which and where you're heading when you first get in a car, but after a few twists and turns without the chance to reorient yourself, you may suddenly feel like you've lost your way - even if a GPS or map tells you otherwise. This is especially true if you happen to take a nap or close your eyes.

This is a prime example of a temporary failure in what researchers think is the mammalian brain's 3D compass - a compass that relies on the positioning of objects relative to you, not the magnetic poles.

A study recently published in the journal Nature details how bats are ideal for studying this mechanism because the animals are constantly swooping, diving, and even flying upside-down to snag their midnight snacks. Even with the help of their sonar, keeping track of where they are and what direction they are in can be challenging, so how do they do it? (Scroll to read on...)

According to a team of Israeli scientists, the brain of the Egyptian fruit bat pulls off this incredible feat with the help of special "3D" neurons that can tell which way its head is pointing.

Using a video-monitoring system and microelectrodes that they inserted in the bats' brains, the researchers tracked bats while they flew and crawled. They compared brain signals with the direction they were facing and quickly determined that these special neurons are a different set than those that help mammals compute 2D direction.

"Basically what we found is that if you want to direct your head at a tree branch that's at a certain elevation and angle from you, you want to compute this [in a] 3D direction," Arseny Finkelstein, a co-author of the study, told The Verge. "This '3D head direction cell' can do that."

The research team even suggests that the sensation of vertigo is a direct result of these neurons failing to fire properly, with the 2D neurons trying to compute 3D movement.

Interestingly, comparing this system to a traditional compass is not exactly ideal, as a compass is all about 2D movement. Similarly, angles would indicate a sphere-like shape, and don't involve the amount of functional representation that is needed. Instead, the researchers believe that the neurons fire based on relative position best described by a donut, as shown below.

The researchers also explained in an interview with Haaretz that this same cellular "compass" set is likely present in humans as well, and is heavily dependent in our short term ability to remember our relation to surroundings we just saw.

"We think the navigation system that evolved in animals enables humans to remember location-based special memory," Finkelstein said, adding that it's not only about remembering that you had been somewhere, but what you did there (did you turn right? Did you climb up?).

"We think these compass and location cells constitute a sort of scaffolding on which we 'hang' our memories."

In the future, the researchers hope to investigate how exactly the brain matches these 3D compass signals with those special memories, essentially putting together an image in the brain that says "you are here." Understanding this may help explain the phenomenon of disorientation, and may even lead to preventative measures that would keep pilots and their passengers safer.

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