The midbrain DA neurons play a unique role in basal ganglia and cortical circuits modulating a broad range of behaviors from learning and working memory to motor control. These neurons play a key role in the acquisition of newly acquired behaviors. While the role of DA in reward has been well established,111,112 its primary function is to direct attention to important stimuli likely to bring about a desired outcome.113 Behavioral and pharmacological studies of DA pathways have lead to the association of the mesolimbic pathway and nigrostriatal pathway with reward and motor activity, respectively; more recently, both of these cell groups have been associated with encoding of reward or saliency prediction errors. In this respect, the DA system has been an intense focus of productive research in the development of reward-based learning, drug addiction, and plasticity.114,115
