Bats are flying acrobats. Some twist, turn and swoop wildly through the evening air to snag insects; others execute flips to land and hang upside down from a juicy fruit. The feats seem like a dizzyingly complex maneuvers for muscles—and for bat brains. And it turns out these flying mammals have specific neurons that help them create a kind of three-dimensional compass. But, perhaps even more surprisingly, the researchers who discovered this also suspect that humans have a similar internal GPS.
This is not a compass in the sense that the system differentiates north from south, explains Ruth Schuster for Haaretz. Rather, it helps bats determine which way is up, down and to either side.
The finding, published in the journal Nature, builds on previous work on how animals create an internal map of their surroundings. In the early 1970s, research at the University College London first revealed directionally-tuned neurons in the hippocampus of rats—cells that fired only when the rats were in a specific part of their enclosure, reports Mo Costandi for The Guardian. The mid-1980s brought the discovery of head-direction cells that fired when a rat faced in a certain direction; Norway-based researchers identified so-called grid cells that fired as the rat crosses across an enclosure and border cells that help the rat keep track of the edges of its environment. For their work on the brain’s 3D positioning system, three researchers were recognized with this year’s Nobel Prize in Physiology.
But the work thus far was on rats, which are necessarily confined to the ground. Arseny Finklestein and his colleagues of the Wiezmann Institute of Science pinpointed the up-and-down cells that make the internal map three-dimensional. Egyption fruit bats carrying wireless microelectrodes in their brains helped the researchers figure this out. Costandi writes:
The recordings taken during flight confirmed that the bat’s neural compass encodes space in three dimensions. About one fifth of the cells were tuned to specific ranges of pitch, firing only when the bats flew at a certain angle in the vertical plane, and about one tenth to roll angles. A significant proportion of the cells were sensitive to a combination of angles in the horizontal and vertical planes, and some to angles in all three planes.
"And we don’t think our results are specific to bats," Finkelstein told BBC News. Although rats and bats are millions of years apart, evolutionarily speaking, they have the same kind of cells: place cells, head-direction cells and grid cells. "That’s why we think this might be relevant for humans too."
The cells may not only be important for not bumping into things, but also for remembering where specific events happened. "We think these compass and location cells constitute a sort of scaffolding on which we 'hang' our memories," Finklestien told Haaetz.com.
Understanding how the system works in humans could help explain why fighter pilots, for example, experience vertigo sometimes and can’t tell up from down, writes Schuster for Haaretz. It also applies in less life-threatening situations—when you are disoriented after exiting the subway, say. Blame it on a failure of your 3D navigation cells.