Dopamine scales performance in the absence of new learning.

Learning and motivation are integral in shaping an organism's adaptive behavior. The dopamine system has been implicated in both processes; however, dissociating the two, both experimentally and conceptually, has posed significant challenges. We have developed an animal model that dissociates expression or scaling of a learned behavior from learning itself. An inducible dopamine transporter (DAT) knockdown mouse line has been generated, which exhibits significantly slower reuptake of released dopamine and increased tonic firing of dopamine neurons without altering phasic burst firing. Mice were trained in experimental tasks prior to inducing a hyperdopaminergic tone and then retested. Elevated dopamine enhanced performance in goal-directed operant responses. These data demonstrate that alterations in dopaminergic tone can scale the performance of a previously learned behavior in the absence of new learning.