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.
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.
ILLUSTRATION BY MATTHEW TWOMBLY, NGM ART
An artist's rendering of a dragonfly shows an electronic
backpack that helps scientists at the Howard Hughes Medical Institute study the
way it flies.
Controlling Movement
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.
Slow Motion
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."
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