After further trials, Yang concluded that a pregnant fly will lay eggs on a sugary medium if that's the only choice, but if there is a non-sweet alternative, it will opt for that side. Why? Yang can't say for sure, but she speculates that perhaps the bitter location is less likely to attract predators that could jeopardize the offspring. "The fly's response to the sucrose medium isn't automatic," the researcher notes. "Its decision to accept or reject the sweet medium as an egg-laying site appears to depend on the availability of 'better' options." Yang has identified some of the nerve pathways that control egg laying, and she plans to use genetic tools to further analyze simple decision making in animals.

"Her work really opens up a whole area," comments Yuh Nung Jan, Yang's mentor. "Because once we know there is this robust behavior for decision making, we can bring in all our techniques, already developed as well as new, to follow up and get at what might be components of the circuit."

Behavioral choices are the nitty-gritty of sheer animal survival as well as the engine of advanced human culture. HHMI scientists are betting that understanding these decision-making circuits in relatively simple settings will ultimately expose the brain mechanisms responsible for higher cognitive capacities in humans. As Shadlen argues, "even human consciousness is mediated by relatively simple, unconscious decisions to engage the environment."

FOR MORE INFORMATION and to see reproductions of experimental trials from Michael Shadlen's study, visit www.shadlen.org/mike/movies/ProbClass/Abstract.html.

		Daunting feats of miniaturization stand between Vivek Jayaraman and the contraption he is building to read the minds of Drosophila in real time. "Our goal is to understand the neural computations underlying decision making in response to sensory input," says Jayaraman, a Janelia Farm fellow. "We use the fly because its nervous system is simpler and we can use genetic tools to study circuit computation at a level of detail not possible in larger systems." Using microsurgical tools and steady hands—Jayaraman says he has sworn off coffee to do this work—the researchers can expose the brain of the fly while its body and head are tethered in place with wax or glue, leaving its legs free to move. Hairlike microelectrodes are inserted into the brain of the one-eighth-inch-long insect to record activity in individual neurons, while a two-photon microscope obtains visual imagery of larger brain regions and populations of neurons. Jayaraman and his postdocs, Eugenia Chiappe and Johannes Seelig, are next planning a center-stage juggling act: they are developing a system in which a tiny ball, less than one-quarter inch in diameter, is supported on an air column, like a pingpong ball over a stream of air from a mini leaf-blower. The fly, tethered to its recording device, will be lowered until its feet touch the ball. "As the fly moves its legs in response to visual inputs," says Jayaraman, "we'll record the movements of the ball and infer what the fly wants to do. We hope this setup will allow us to link neural processing to decision-making behavior." —R.S.

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