Dual system theories suggest that behavioral control is parsed between a deliberative "model-based" and a more reflexive "modelfree" system. A balance of control exerted by these systems is thought to be related to dopamine neurotransmission. However, in the absence of direct measures of human dopamine, it remains unknown whether this reflects a quantitative relation with dopamine either in the striatum or other brain areas. Using a sequential decision task performed during functional magnetic resonance imaging, combined with striatal measures of dopamine using [ 18 F]DOPA positron emission tomography, we show that higher presynaptic ventral striatal dopamine levels were associated with a behavioral bias toward more model-based control. Higher presynaptic dopamine in ventral striatum was associated with greater coding of model-based signatures in lateral prefrontal cortex and diminished coding of model-free prediction errors in ventral striatum. Thus, interindividual variability in ventral striatal presynaptic dopamine reflects a balance in the behavioral expression and the neural signatures of model-free and model-based control. Our data provide a novel perspective on how alterations in presynaptic dopamine levels might be accompanied by a disruption of behavioral control as observed in aging or neuropsychiatric diseases such as schizophrenia and addiction.dopamine | decision making | reinforcement learning | PET | fMRI H uman choice behavior is influenced by both habitual and goal-directed systems (1). For example, having enjoyed a delicious dinner makes another subsequent visit to the same restaurant more likely. Upon returning at a later point, another visit could happen reflexively when walking past the restaurant, or alternatively be planned and involve reflection, for instance, by checking recent customer reviews to bolster against possible changes. These two decision modes differ fundamentally in terms of their control over actions and associated outcome consequences. Reflexive habitual preferences are retrospective and arise from a slow accumulation of rewards via iterative updating of expectations (2), for example by repeating dinner at the same place after having previously enjoyed tasty food there. In contrast, goal-directed behavior requires a prospective consideration of future outcomes associated with a set of actions (3). For example, knowledge that the chef has changed and subsequent reviews have been less good should reduce one's expectations. Thus, in the face of such change, a goaldirected system can adapt quickly, whereas a habitual system needs to experience an actual outcome before it can alter behavior in an adaptive manner (4). This dual-system theory has been formalized within computational models of learning that update expectations based on past rewards ("model-free") or map possible actions to their potential outcomes ("model-based") (5). There is evidence that model-based learning signals during the acquisition of task structure are encoded within prefrontal-parietal cortices, where...