Now here’s the tricky part of the experiment. The lights on the screen were positioned so that only one of them was in the field of view accessible to the nerve cell being monitored. When the accessible light appeared, that nerve cell fired electrical impulses, as nerve cells do when stimulated. That nerve cell also boosted its activity as the monkey’s eyes moved to gaze at that light. No surprises there. But if that light happened to be the “high reward” light, the nerve cell fired its signals much more vigorously than when viewing the “low reward” light. To an old-school neurophysiologist, that would be surprising. For the actual visual stimulus was precisely the same in either case—a light comes on, and the eyes move to look at it. Somehow the neuron linked to that visual stimulus “knew” which light was the Big Gulp of juice dispensers. The monkey’s choice of looking toward the high-reward light (that is, the utility-maximizing choice) reflected a specific change in activity by a nerve cell in a specific region of the brain.8

Of course, that experiment was just a start, but it opened a lot of scientists’ eyes to the possibility of understanding economic decision making by looking inside the brain. The next year, neuroeconomics pioneers met in Princeton for the first major conference on the topic. Montague recalls the skepticism expressed by one of the economists attending, who saw no reason to believe that brain chemicals had anything to do with economics. “I said that is just complete poppycock,” Montague recalled. “If your brain doesn’t generate economic behavior, what kind of ghost horses do you believe in?” Even worse, the economist didn’t even think his remarks were particularly provocative. “I was stunned by that,” said Montague. “I might still be stunned by that.”9

Gradually, though, the idea of merging neuroscience and economics caught on, though perhaps more rapidly in neuroscience than economics. A special issue of Neuron, published in October 2002, included a passel of papers on human decision making, many of them exploring the new insights offered by neural economic studies.

Montague and Berns’s paper in that issue argued that the

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