Opiate reinforcement processes: re-assembling multiple mechanisms

Opiate reinforcement processes can be described within the context of operant conditioning theory. Both positive and negative reinforcing effects may motivate drug-taking behavior, although the strongest evidence attributes drug-taking to a simple positive reinforcement process. Empirical research has focused largely on a positive reinforcement mechanism involving the ventral tegmental dopamine system, but three additional reinforcement mechanisms can be argued on logical grounds. These other mechanisms involve neuroadaptive changes produced by chronic opiate administration and may contribute to the strong motivational impact of opiates following long-term drug use.