By watching fruit flies take flight, Gwyneth Card is trying to learn how the brain makes decisions and then translates those decisions into action.
The path that brought Card to this research started at Harvard University, where she conducted an undergraduate research project with Andrew Biewener, an expert in the biomechanics of animal movement. "It was a great experience," she says. "We went to Australia and chased kangaroos and wallabies to study the mechanics of how they hop." Card and Biewener recorded the forces generated by these animals as they hopped over force plates—scale-like instruments used to measure movement—embedded in the ground.
As she was conducting this research, Card realized that to truly understand how animals move she would also have to study the body's control center—the brain. That insight brought her to the neuroscience laboratory of Simon Laughlin and Holger Krapp at the University of Cambridge, where she spent a year learning how to conduct brain recordings—or electrophysiology—in house flies. With this expertise, Card returned to her home state of California to pursue a Ph.D. at the California Institute of Technology. There, under the supervision of Michael Dickinson, she started looking at how the fruit fly Drosophila melanogaster initiates flight.
When a fly is confronted with a looming object, it performs a carefully choreographed set of maneuvers that enable it to take off in flight and escape possible danger. Card looked at these motions in minute detail by taking high-speed videos of the flies as they launched into flight. She then examined the videos frame by frame, measuring the positions of legs, wings, and other body parts over time.
What her studies reveal is that a fly's escape responses are much more sophisticated and complex than anyone had appreciated. Card described sets of distinct behavior "modules" that the fly performs in a matter of milliseconds. These behaviors vary depending on the information the fly receives from its senses—such as the position of a looming object or the speed at which it is approaching—and include not just wing raising and leg extension, as previously thought, but also other behaviors, such as freezing, leg position adjustment, and leaning.
In addition, Card found that although a set of modules may follow a certain sequence in response to a particular stimulus, each one appears to be independent—that is, each module may occur regardless of whether others have been performed.
At Janelia Farm, Card plans to determine how these behavioral modules and neuronal components interact. One of the attractions of the Janelia Farm environment is the "wonderful support and expertise available for collaboration on these kinds of studies," says Card. A key resource is the availability of genetic tools for creating mutations in fly genes that are known to govern the functions of particular neurons. "We'll create genetic modifications that obliterate certain populations of neurons and then see if the flight behavior of the fly changes," says Card. "In this way we can narrow down the neurons involved in a behavior, which we can then further study by electrophysiology."
By combining genetics and electrophysiology with detailed behavioral analyses, Card hopes to soon be able to unravel how the fly decides which maneuvers to make while taking off in flight. And such understanding may provide insights into the decision-making process in general, even when it comes to more complex choices. "The decision to have coffee or tea in the morning probably does not come down to a single neuron in humans," says Card. "But the fly has a relatively simple system in comparison and it might be possible to understand decisions at the neuronal level."
