Economists model what people want by introducing these things into the utility function. As a rule, goods and services belong in utility, but not money. This is because money buys goods and services, but is not itself consumed (except by currency collectors.) This has led to models where people indirectly value money and a recognition that money only works when people are willing to accept it as payment. Recently neuroscientists interested in studying people had to come up with ways of rewarding them when they were in the scanner. Their answer, also the answer in experimental economics, is to pay them for their decisions. So what happens in the brain when people get paid? Brian Knutson and colleagues pay subjects based on their success in responding quickly to a visual target. In their paper "Anticipation of monetary reward selectively recruits nucleus accumbens," they varied the size of the reward and found that dopamine rich areas (such as the nucleus accumbens) showed bold responses proportional to the magnitude of the monetary reward anticipated by the subject. The nucleus accumbens also responds to more basic rewards. But this may mean that the brain learns to put things, like money, in the utility function and that economists’ theory of preferences should take into account how utility is learned.