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Michael Shadlen (right) and Cornelia Bargmann study decisions in animals to gain insights into higher cognition.
Researchers, including HHMI scientists, have already done prodigious work over several decades to piece together how animal and human nervous systems detect sensory information—especially sights, odors, and tastes—and encode it in electrical signals in the brain. For example, HHMI investigator William Newsome, at Stanford University, identified specific neurons in monkeys that detect the direction in which an object is moving. On the output side, Newsome and others have mapped circuits that direct motor activity, such as a monkey's eye movements in response to a stimulus.
Bargmann and HHMI investigator Michael Shadlen, among others, want to uncover the critical cells and circuits that complete the chain from input to output—the bridge between sensation and action. Exploring this arena provides "a window on higher brain function," says Shadlen, a neurobiologist at the University of Washington. He's especially interested in "how humans and other complex animals take a bit of evidence from the world and hold onto it for later use, or combine it with other information."
With new tools and experimental designs that range from straightforward to elaborate, HHMI researchers are devising the means to observe and map decision making in simple organisms and complex primates. They are observing risk assessment and survival choices made by worms and flies—for themselves as well as for their offspring. Studies of monkeys are revealing circuitry involved in more sophisticated learning and keeping track, or playing the odds. Ultimately, they hope to understand higher cognitive abilities such as reasoning and deliberation. One thing made clear by these early studies: "thinking" like a statistician is not exclusive to humans.
Human studies in psychology explain human choice behavior in economic, medical, ethical, and crisis situations, among others. Peering into the brain itself, functional MRI devices can locate activity in the cortex as people perform decision-related tasks. Such experiments have identified particular brain areas and structures that appear to be crucial, but the methods do not have sufficient resolution to tease out the exact neural wiring involved. For this reason, among others, experimental animals of several types offer numerous advantages.
Scientists like Shadlen want the details. He is seeking answers "at the level where single neurons are discharging and making decisions," he says. "You can't study that with functional imaging."
As monkeys play visual discrimination games that require a correct choice to win a reward, Shadlen records activity in groups of single brain neurons. He varies the rules of the games to test different components of the decision process and determine how they are represented in the ebb and flow of neural activity.
Photos: Shadlen: Charles Peterson, Bargmann: Matthew Septimus