Introduction Fluid intelligence expresses the capacity for interpretation of novel stimuli and flexible behavioral adaptation to such cues. Phasic dopamine firing closely matches a temporal difference prediction error (PE) signal important for learning and rapid behavioral adaptation. Both fluid intelligence and dopaminergic neurotransmission decline with age. So far, no study investigated the relationship between fluid IQ, PE signal and direct measures of dopaminergic neurotransmission. Here we used a multimodal imaging approach that combines positron emission tomography and functional magnetic resonance imaging. Methods A group of healthy controls was investigated with both 6-[18F]FluoroDOPA PET and functional MRI with a probabilistic reversal task. The task required a constant behavioral adaptation to changes in reward contingencies, while choosing between two abstract stimuli. A reinforcement learning algorithm was used to compute a trial-by-trial prediction error, which was the used as a regressor in the fMRI data analysis with SPM8. Results The prediction error signal was associated with functional activation in the basal ganglia including the ventral striatum and putamen. Fluid intelligence was associated with the PE signal in the ventral striatum, which correlated with age-related changes in dopamine synthesis capacity in the prefrontal cortex. Conclusion These findings provide insight into the role of age-related changes in dopaminergic neurotransmission on behavioral adaptation. The multimodal imaging approach allows the characterization of interactions between dopamine metabolism and learning-related neuronal activation and may thus be a useful tool to clarify mechanisms underlying learning and plasticity in old age, which are crucial to our understanding of successful aging.

Overweight and obesity is a health threat of increasing concern and understanding the neurobiology behind obesity is instrumental to the development of effective treatment regimes Serotonergic neurotransmission is critically involved in eating behaviour: cerebral level of serotonin (5-HT) in animal models is inversely related to food intake and body weight and some effective anti-obesity agents involve blockade of the serotonin transporter (SERT) We investigated in 60 healthy volunteers body mass index (BMI) and regional cerebral SERT binding as measured with [C-11]DASB PETIn a linear regression model with adjustment for relevant covariates, we found that cortical and subcortical SERT binding was negatively correlated to BMI (-0 003 to -0 012 BPND unit per kg/m(2)) Tobacco smoking and alcohol consumption did not affect cerebral SERT bindingSeveral effective anti-obesity drugs encompass blockade of the SERT, yet, our study is the first to demonstrate an abnormally decreased cerebral SERT binding in obese individuals Whether the SERT has a direct role in the regulation of appetite and eating behaviour or whether the finding is due to a compensatory downregulation of SERT secondary to other dysfunction(s) in the serotonergic transmitter system, such as low baseline serotonin levels, remains to be established (C) 2010 Elsevier Inc All rights reserved