If you enter a darkened room, your brain can lead you to the light switch because it's kept track of landmarks and where you've been moving - and fruit flies can do the same thanks to a "compass ring" of cells in their brain, researchers have found.
Researchers from the Howard Hughes Medical Institute's Janelia Research Campus in Virginia report they've been able to see the "compass" in action.
Using a microscope to peer into the brain of a fly walking around a spherical treadmill, they saw brain activity sweep around the ring of cells to match the direction in which the insect was heading, they've reported in the journal Nature.
And when they turned the lights out and left the fly in the dark, the compass-like activity in the doughnut-shaped ring of brain cells continued, they said.
"The fly is using a sense of its own motion to pick up which direction it's pointed," says senior study author Vivek Jayaraman.
Understanding how fruit flies navigate in their environment could help in understanding how humans achieve the task, the researchers say.
In some other insects, like locusts and butterflies, researchers have seen brain cells reacting to the insects' position in relation to polarized light in the sky, in effect creating a "sun compass."
However, the fruit fly's compass - given that it works in the dark as well - is much more like "head direction cells" found in mammals that determine directional navigation based on landmarks sensed in the local environment, the researchers say.
In mammals, those cells are scattered throughout the brain, whereas in the fly they seem concentrated in a brain area known as the ellipsoid body, which just happens to be circular - just like a compass.
That provided a perfect target to watch for brain activity as the fly navigated, the researchers noted.
"It's very seldom that you have a compass in the brain that really looks like a compass," Jayaraman says.
The researches found that the compass cells could hold a memory of the fly's orientation, allowing it to keep its bearings even when it had been standing still in the dark for as long as 30 seconds.
"We are seeing how a little insect's brain can do things not very different from our own," says Jayaraman.
"The bottom line is that I think we're starting to see increasing evidence that the fly may have a lot to tell us about how our own brains work, even when it comes to more complex aspects of cognition," he says.
