Experimental economists know that people prefer games involving known risks, not ambiguous ones. Now they have a better idea why. Researchers from the California Institute of Technology had volunteers play two games while undergoing brain-imaging scans. In one game, subjects could take a small sum of money or potentially win a larger sum by guessing the color of a card drawn from a deck they knew was split evenly between two colors. The second game was identical except that subjects did not know the proportions of the cards. This more ambiguous game activated the amygdala and orbitofrontal cortex, brain areas associated with emotion processing, whereas the game of known risk did not. The result lends credence to a model in which people caution themselves to avoid the worst possible outcome, as opposed to coolly identifying the best strategy, according to a commentary in the December 9, 2005, Science.