Decreased volume of the brain reward system in alcoholism

Background: Reinforcement of behavioral responses involves a complex cerebral circuit engaging specific neuronal networks that are modulated by cortical oversight systems affiliated with emotion, memory, judgment, and decision making (collectively referred to in this study as the "extended reward and oversight system" or "reward network"). We examined whether reward-network brain volumes are reduced in alcoholics and how volumes of subcomponents within this system are correlated with memory and drinking history. Methods: Morphometric analysis was performed on magnetic resonance brain scans in 21 abstinent long-term chronic alcoholic men and 21 healthy control men, group-matched on age, verbal IQ, and education. We derived volumes of total brain and volumes of cortical and subcortical reward-related structures including the dorsolateral-prefrontal, orbitofrontal, cingulate cortices, and the insula, as well as the amygdala, hippocampus, nucleus accumbens septi (NAc), and ventral diencephalon. Results: Morphometric analyses of reward-related regions revealed decreased total reward-network volume in alcoholic subjects. Volume reduction was most pronounced in right dorsolateral-prefrontal cortex, right anterior insula, and right NAc, as well as left amygdala. In alcoholics, NAc and anterior insula volumes increased with length of abstinence, and total reward-network and amygdala volumes correlated positively with memory scores. Conclusions: The observation of decreased reward-network volume suggests that alcoholism is associated with alterations in this neural reward system. These structural reward system deficits and their correlation with memory scores elucidate underlying structural-functional relationships between alcoholism and emotional and cognitive processes.