Individuals make choices and prioritize goals using complex processes that assign value to rewards and associated stimuli. During Pavlovian learning, previously neutral stimuli that predict rewards can acquire motivational properties, becoming attractive and desirable incentive stimuli. However, whether a cue acts solely as a predictor of reward, or also serves as an incentive stimulus, differs between individuals. Thus, individuals vary in the degree to which cues bias choice and potentially promote maladaptive behaviour. Here we use rats that differ in the incentive motivational properties they attribute to food cues to probe the role of the neurotransmitter dopamine in stimulus–reward learning. We show that intact dopamine transmission is not required for all forms of learning in which reward cues become effective predictors. Rather, dopamine acts selectively in a form of stimulus–reward learning in which incentive salience is assigned to reward cues. In individuals with a propensity for this form of learning, reward cues come to powerfully motivate and control behaviour. This work provides insight into the neurobiology of a form of stimulus–reward learning that confers increased susceptibility to disorders of impulse control. Humans and animals readily learn to associate neutral cues that are associated with rewards. Dopamine release is known to play some part in this learning, but its exact role (and hence what may be disrupted in disorders such as drug addiction) is controversial. Does it predict the arrival of the actual reward, or does it make the cues rewarding in their own right? To investigate, Flagel et al. exploited rat strains that have been selectively bred for many generations to have a greater or lesser propensity to attribute incentive properties to neutral cues associated with food rewards. Using cyclic voltammetry, the authors measure dopamine signals in the different strains and examine the effect of blocking dopamine. They conclude that dopamine selectively mediates motivational, rather than predictive, aspects of the cues. Humans and animals readily learn to associate neutral cues paired with rewards, but the exact role that dopamine release has in this learning is controversial. Using previously established rat strains selectively bred for many generations to have greater or lesser propensity to assign value to learned cues, this study uses cyclic voltammetry to measure dopamine signals in the different strains and also examines the effect of blocking dopamine. It is concluded that dopamine selectively mediates motivational, rather than predictive, aspects of the cues.

A selective role for dopamine in stimulus–reward learning