It should be noted that in the studies described above, subjects were not asked to choose between monetary rewards. We predict that choice would similarly follow a linear function (choice of higher over lower reward) in healthy controls more so than in addicted individuals, who we expect to show less flexibility in choice (choosing drug over other reinforcers), particularly during craving and bingeing. Studies that allow subjects to choose between reinforcers have mostly been conducted in laboratory animals. These studies have shown that, when given the choice, previously drug-exposed animals choose the drug over novelty85, adequate maternal behaviour86 and even food87–89, indicating that drug exposure can decrease the perceived value of natural rewards, even those that are needed for survival. In a recent human neuroimaging study in which subjects could win cigarettes or money, occasional smokers were more motivated to obtain money than cigarettes, whereas dependent smokers made similar efforts to win money or cigarettes90. A similar group by reward interaction was observed in the right OFC, bilateral DLPFC and left ACC, such that in the occasional smokers these regions
