Changes in brain activation associated with reward processing in smokers and nonsmokers

Tobacco smoking is the most frequent form of substance abuse. Several studi es have shown that the addictive action of nicotine is mediated by the meso limbic. dopamine system. This system is implicated in reward processing. In order to better understand the relationship between nicotine addiction and reward in humans, we investigated differences between smokers and nonsmoke rs in the activation of brain regions involved in processing reward informa tion. Using [(H2O)-O-15] positron emission tomography (PET), we measured re gional cerebral blood now (rCBF) in healthy smokers and nonsmokers while th ey performed a prelearned, pattern-recognition task. We compared two condit ions involving nonmonetary reinforcement or monetary reward with a baseline condition in which nonsense feedback was presented. With monetary reward, we found activation in the frontal and orbitofrontal cortex, occipital cort ex, cingulate-gyrus, cerebellum, and midbrain in both groups. Additionally, monetary reward activated typical dopaminergic regions such as the striatu m in nonsmokers but not in smokers. We found a similar pattern of activatio n associated with nonmonetary reinforcement in nonsmokers, whereas activati on was found in smokers only in the cerebellum. The different patterns of a ctivation suggest that the brains of smokers react in a different way to re ward than those of nonsmokers. This difference involves in particular the r egions of the dopaminergic system including the striatum. In principle thes e observations could be interpreted either as a consequence of tobacco use or as a primitive condition of the brain that led people to smoke. Supporte d by related nonimaging studies, we interpret these differences as a conseq uence of tobacco smoking, even if a short-term effect of smoking prior to t he experiment cannot be excluded.