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...

The results indicate that verbal memory impairments were possibly aggravated after prolonged ecstasy abstinence while there was tentative evidence of serotonergic recovery. On the other hand, self-reported elevated psychopathology appeared to be associated with polydrug use in general and not specifically with ecstasy use.

The aim of this study was to examine the prevalence, distribution, and topographic relationship of vascular 18 F-sodium fluoride uptake and arterial calcification in major arteries. Methods: Image data obtained from 75 patients undergoing whole-body 18 F-sodium fluoride PET/CT were evaluated retrospectively. Arterial radiotracer uptake and calcification were analyzed qualitatively and semiquantitatively. Results: 18 F-sodium fluoride uptake was observed at 254 sites in 57 (76%) of the 75 study patients, and calcification was observed at 1,930 sites in 63 (84%) of the patients. Colocalization of radiotracer accumulation and calcification could be observed in 223 areas of uptake (88%). However, only 12% of all arterial calcification sites showed increased radiotracer uptake. Conclusion: Our data indicate the feasibility of 18 F-sodium fluoride PET/CT for the imaging of mineral deposition in arterial wall alterations. 18 F-sodium fluoride PET/CT may provide relevant information about the morphologic and functional properties of calcified plaque.

Background Patients with encephalitis associated with antibodies against N-methyl-D-aspartate-receptor antibody (NMDAR-ab) encephalitis frequently show psychotic symptoms, amnesia, seizures and movement disorders. While brain MRI in NMDAR-ab encephalitis is often normal, abnormalities of cerebral glucose metabolism have been demonstrated by positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) in a few usually isolated case reports. However, a common pattern of FDG-PET abnormalities has not been reported. Methods The authors retrospectively identified six patients with NMDAR-ab encephalitis in two large German centres who underwent at least one whole-body FDG-PET for tumour screening between January 2007 and July 2010. They analysed the pattern of cerebral uptake derived from whole-body PET data for characteristic changes of glucose metabolism compared with controls, and the changes of this pattern during the course of the disease. Results Groupwise analysis revealed that patients with NMDAR-ab encephalitis showed relative frontal and temporal glucose hypermetabolism associated with occipital hypometabolism. Cross-sectional analysis of the group demonstrated that the extent of these changes is positively associated with clinical disease severity. Longitudinal analysis of two cases showed normalisation of the pattern of cerebral glucose metabolism with recovery. Conclusions A characteristic change in cerebral glucose metabolism during NMDAR-ab encephalitis is an increased frontotemporal-to-occipital gradient. This pattern correlates with disease severity. Similar changes have been observed in psychosis induced by NMDAR antagonists. Thus, this pattern might be a consequence of impaired NMDAR function.