Our dopaminergic reward system is particularly sensitive to intermittent reinforcement. When a behavior is intermittently reinforced, the reward for a given behavior is irregular and unpredictable. Dopamine neurons are particularly sensitive to novelty and surprise, so when behavior is unpredictably reinforced, each experience of reward comes as a surprise. In fact an unpredicted reward is perhaps three to four times as activating as a predictable reward. This pattern contributes to our vulnerability to gambling, which is defined by intermittent reinforcement.