Dagher and his colleague Deb Tang recruited 29 volunteers for the study and, asked them to rate how much they liked various items of food, from chocolate cookies and potato crisps to apples and carrots.

　　recruit v. 招募

　　The scientists next put the volunteers in a brain scanner and had them bid up to five dollars a time for food and other objects, such as baseball caps and T-shirts, that flashed up on a screen.

　　After each volunteer had bid for 300 items, one bid was taken and compared with a counterbid generated at random by a computer. If the volunteer bid the most, they got to eat the food or keep the item at stake.

　　at random 随机的；任意的

　　at stake 在紧要关头

　　Each person took the test twice over two days and beforehand received either an injection of ghrelin, a hunger hormone that is released by the stomach, or a shot of saline as a control. The ghrelin jab made volunteers ravenous for one to two hours.

　　Unsurprisingly, the hungry volunteers bid consistently more for food and less for inedible items than the volunteers who had the saline jab. The hungry people were willing to spend an average of $2.09 for food and $1.32 for other objects, but on saline bid only $1.82 for food and $1.58 for the inedible items.

　　The scientists traced the behaviour to increased activity in a brain region called the ventromedial prefrontal cortex, which is involved in motivation and reward.

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