In a windowless room in northern Virginia, neuroscientist Anthony Leonardo is about to open a door. Quickly. "There are thousands of fruit flies in there, and we don't want them all to escape," he says.
The fruit flies aren't research subjects. They're food. Leonardo studies how dragonflies catch their prey on the wing. To do that, he and his colleagues are working on a new invention: a backpack that can record from a dragonfly's nerve cells while it's chasing a fruit fly.
Leonardo works at the Howard Hughes Medical Institute, which funds scientists like him fully so they don't have to spend time applying for grants or mentoring students. Many are at universities, but Leonardo works at HHMI's research facility, Janelia Farm, in Ashburn, Virginia.
The fruit flies and dragonflies live in a dragonfly flight arena—really, that's what the sign by the door says. It's a brightly lit room kept toasty and humid. To make the dragonflies think they're outside on a warm summer day, the walls are covered with photomurals of an outside landscape—bright yellow flowers in the foreground, bushy evergreen trees in the background. A handful of dragonflies rest on the walls or cameras, occasionally going after a fruit fly.
When the cameras in the room are turned on, Leonardo can record the insects' every move, tracking them as they pull off precision maneuvers with their four wings.
Intercepting a moving object looks effortless. An outfielder gets his eye on the ball. He runs, he sticks out his glove, and smack! But at the level of the nerve cells, it's really complicated.
"This is a pretty common problem we take for granted," Leonardo says. When you're catching a ball, you're doing two things at once: keeping track of the thing you want and going after it. The dragonfly is tracking the fly's movement—and, at the same time, getting oriented so it can stick out all six legs, lay them on its prey, and jam that tasty fly in its mouth. "We understand very little about how the brain integrates this sensory and motor information," he says.
Leonardo studies this problem in dragonflies, not humans or mice, partly because they're so agile and beautiful, but mostly because they're relatively simple. They have fewer neurons in their brain, which means it's easier to measure what's going on.
For insects, though, dragonflies are pretty big, which means they're relatively easy to work with. For example, you couldn't stick a backpack on a house fly. But that's just what Leonardo and his colleagues are doing with dragonflies.
In his lab upstairs, Leonardo demonstrates how the backpacks are assembled. He glues together the silver wire and carbon fiber that make an antenna, cuts out a little green chip, and glues the assembly together. Later the whole thing is glued onto a dragonfly's shoulders.
Older iterations of the backpack were too heavy; while the dragonflies could fly if prodded, they didn't want to forage and would quickly starve to death. By ditching the teensy battery, Leonardo and his colleagues were able to make the backpack weigh only 40 milligrams, about as much as a couple of grains of rice, and small enough that the dragonflies will forage while they wear it.
The backpack also has a tiny wire leading to probes that hook into individual neurons in the dragonfly equivalent of a spinal cord. "While the animal is performing this sophisticated interception behavior, that little backpack is acting like a radio that's broadcasting the signals from those neurons back to our computer," Leonardo says.
That's the idea, anyway. There's still one hurdle: figuring out exactly how to put the probes in so they won't annoy the dragonflies. "It's like if I'd put a pebble in your shoe and asked you to dance," Leonardo says. His team is still working on how to place the probes so the dragonflies will dance.
Leonardo has already learned a lot about how dragonflies think just by watching them work. High-speed video cameras show dragonflies and fruit flies converging in slow motion. He's also worked out how to do motion capture on the dragonflies, as if they were being recorded for an animated movie. The researchers stick tiny reflective dots on a dragonfly in several places, and an array of infrared cameras records just how its body bends and turns as it flies.
It seems that the dragonfly catches its prey by keeping the fly in the same place in its visual field and flapping so that it gets closer, which was what people thought—but Leonardo is working out how the way its body works determines how it actually moves.
"Like, if you were driving from D.C. to Boston, you can't drive in a straight line," he says. "There are other constraints that dictate that."
"It's amazing work," says Adrienne Fairhall, a computational neuroscientist at the University of Washington. "We don't have very many examples of small populations of neurons that we can really understand."
Brains are so incredibly complicated—a human brain (see photos) has billions of cells, constantly sending each other signals—that it's rare to figure out the answer to even one question like this one. The backpacks are impressive, too, she says. "It's a wonderful example of being able to push the technology."