By studying brain activity in bats, researchers reveal that their neural navigation system acts in three dimensions. This internal compass gives them a continuous sense of direction and location, making it possible for them to orient themselves in dark, complex settings swiftly. The findings were published in Nature earlier this month.
We’ve all been disoriented before. If you go up a series of stairs after getting out of a subway, you might need a minute to regain your sense of direction. To avoid aerial crashes, pilots must guard against vertigo and be able to tell up from down all the time. Researchers think that disorientation is caused by a temporary malfunction of a brain circuit that operates our 3D compass.
To see how the sense of direction is maintained in nature’s aerial acrobats, a Weizmann Institute of Science team led by Arseny Finkelstein and Nachum Ulanovsky recorded neural activity in the brains of Egyptian fruit bats while they’re flying and crawling by using microelectrodes implanted in the presubiculum area. The team also used video to monitor the angles of their head rotation, and then synced this up with their dataset on neuronal activity.
Certain neurons, they found, seem to always know which way the bat’s head is pointed. These so-called "head-direction" cells track a bat’s direction in 3D as it maneuvers in space by responding to their horizontal and vertical orientations. "This is the first study that's shown any neural correlate to 3D navigation," Finkelstein tells Popular Mechanics. "What we found is that there are basically three types of brain cells—albeit with some overlap—that are sensitive to each one of these dimensions."
Those three types of brain cells, located in different areas, form key components of the navigation system, according to a news release: The "place" and "grid" cells, which work like a GPS, allow bats to keep track of their position, and "head-direction" cells respond whenever the head points in a specific direction, like a compass. The navigation system that we’re used to is a globe with longitude and latitude map coordinates. The special neurons in the bat navigation system, on the other hand, create a donut-shaped, 3D coordinate system that also allows them to know if they're upside down or not, and stay oriented even when inverted. For comparison, the schematics above depict spherical coordinates (left) and "toroidal" coordinates (right).
Meanwhile, another team working on bat navigation overturned some conventional wisdom about Old World fruit bats (right), which have been wrongly labeled as non-echolocating. Their biological sonar works with the echoes created by wing clicks, rather than vocalizations. The work was published in Current Biology this week.
"We did all we could to prove it wrong, including sealing the bats' mouths and anesthetizing their tongues," Yossi Yovel of Tel Aviv University says in a statement. "But nothing stopped them from clicking, except for when we interfered with their wing flaps." In experiments in the dark, these fruit bats were constantly crashing into thick cables, although they were able to discriminate between larger objects—such as an acoustically-reflective black board and a similar-looking cloth sheet."
Yovel adds: "The rudimentary echolocation of the fruit bat is one example of how the first types of echolocation may have evolved."
Images: Merlin D. Tuttle, Bat Conservation International (top), A. Finkelstein et al., Nature (middle), Boonman et al., Current Biology (bottom)