Negative reinforcement in drug addiction: the darkness within.

Drug seeking is associated with the activation of reward neural circuitry, but I argue that drug addiction also involves another major source of reinforcement, specifically negative reinforcement driven by the 'dark side' (i.e., a decrease in the function of normal reward-related neurocircuitry and persistent recruitment of the brain stress systems). This combination forms the antireward system or 'darkness within.' Understanding the neuroplasticity of the neurocircuitry that comprises the negative reinforcement associated with addiction is the key to understanding the vulnerability to the transition to addiction, misery of addiction, and persistence of addiction.