Addicts less sure of rewards.

In Brain General Structure and Function, Brain Science, Memory and Learning by Brainy Days Ahead

Researchers from Radboud University combined 25 studies investigating brain reward sensitivity in more than 1,200 individuals with and without addiction to various substances such as alcohol, nicotine, cocaine, and also gambling. Their analysis of the brain images from these studies revealed an important difference in brain activity between expecting a reward and receiving a reward.

Compared with non-addicted individuals, individuals with substance or gambling addiction showed a weaker brain response to anticipating monetary rewards, but showed a stronger response to receiving the reward. The researchers interpret their findings as a sign that learning problems may lie at the basis of addiction. Reward stimuli constitute an important factor in learning behavior. But if the processing of rewards is disrupted, these individuals may be unable to learn when they can actually expect the monetary reward and may therefore fail to succeed in choosing not to use drugs or not to gamble.