Background and aims: Susceptibility to use of addictive substances may result, in part, from a greater preference for an immediate small reward relative to a larger delayed reward or relative insensitivity to punishment. This functional magnetic resonance imaging (fMRI) study examined the neural basis of inhibiting an immediately rewarding stimulus to obtain a larger delayed reward in smokers. We also investigated whether punishment could modulate inhibitory control. Design: The Monetary Incentive Go/NoGo (MI-Go/NoGo) task was administered that provided three types of reward outcomes contingent upon inhibitory control performance over rewarding stimuli: inhibition failure was either followed by no monetary reward (neutral condition), a small monetary reward with immediate feedback (reward condition) or immediate monetary punishment (punishment condition). In the reward and punishment conditions, successful inhibitory control resulted in larger delayed rewards. Setting: Community sample of smokers in the Melbourne (Australia) area. Participants: Nineteen smokers were compared with 17 demographically matched non-smoking controls. Measurements: Accuracy, reaction times and brain activation associated with the MI-Go/NoGo task. Findings: Smokers showed hyperactivation in the right insula (P<0.01), inferior and middle frontal gyrus (P<0.01), dorsolateral prefrontal cortex (P=0.001) and inferior parietal lobe (P<0.01) both during inhibition of an immediately rewarding stimulus to obtain a larger delayed reward, and during inhibition of neutral stimuli. Group differences in brain activity were not significant in the punishment condition in the right insula and dorsolateral prefrontal cortex, most probably as a result of increased activation in non-smoking controls. Conclusions: Compared with non-smokers, smokers showed increased neural activation when resisting immediately rewarding stimuli and may be less sensitive to punishment as a strategy to increase control over rewarding stimuli.

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Erasmus MC: University Medical Center Rotterdam