Dopamine and Drug Addiction

Dopamine and Reward:
The experience of a reward is accompanied by an emotional state, often described as a feeling of pleasure, satisfaction, well-being, or euphoria. Scientists have determined that the emotional feelings of euphoria or pleasure are related to activity in an area of the brain called the nucleus accumbens (NAC), which is often called the reward or pleasure center of the brain. The amount of activity in the NAC is determined by the levels of a brain chemical called dopamine. Higher levels of dopamine in the NAC are associated with stronger positive feelings of pleasure. For example, eating food induces the release of dopamine into the NAC, which leads to positive feelings of satisfaction and enjoyment.

Natural Rewards and NAC Dopamine:
Food, water, and sex are natural rewards. Each of these natural rewards produces an increase in DA levels in NAC that produces the positive emotional feelings of pleasure and euphoria. The elevated DA activity in NAC produces other effects as well. For example, any stimuli that happen to be present at the time that DA NAC activity is elevated by the natural reward are identified and associated with the positive emotional state produced by the natural reward. So, in addition to producing feelings of pleasure, DA activation of NAC also produces connections to stimuli (people, places, things, sounds, etc) that are present at the time of the euphoric episode. The elevated DA activity in NAC also produces an effect on motor responding called psychomotor activation. Thus, natural rewards induce elevated NAC dopamine, which, in turn produces three different types of effects: the emotional feelings of pleasure, the association of stimuli present during the experience of pleasure, and the motor responses of the psychomotor activation syndrome. It is the interplay among these three functions of the integrated reward system, each of which arise from the activation of the NAC, that constitute the rewarding experience.