Dopamine and Drug Addiction

The Story of the Starving Beast:
An ancient beast is on the verge of starvation. The famished beast picks up a small oblong beige object, looks at it closely, then chews and swallows it. Fortunately, it’s a grain of wheat, a food reward that activates the NAC. The reward system kicks into play, automatically giving rise to feelings of pleasure, accompanied by a pattern of motor activity called psychomotor activation. The beast just ate a piece of food, and psychomotor activation is the physical motor activity pattern that automatically follows, to organize the process of looking for more food. Psychomotor activation begins with a survey of the situation, an investigation of the environment, and a search for more food reward. To better investigate the environment, the beast may stand erect, rearing and sniffing, looking around, visually scanning, evaluating the environment for food. But the food is laying on the ground, scattered among stones, dirt, twigs, and other non-food items. Because the grain of wheat was the item that the beast looked at just before NAC activation, this small oblong beige food object is highly likely to be associated by the NAC with strong feelings of pleasure. The association of the grain of wheat with the emotional state of pleasure will improve the chances that the wheat grain will be selected as the target of the psychomotor activation syndrome. The beast locates on the ground nearby another small beige oblong object, another grain of wheat. Psychomotor activation automatically leads the beast to approach the grain of wheat, pick up the grain of wheat, and eat the grain of wheat. After eating the second grain of wheat, the beast feels another jolt of pleasure, which is experienced right after seeing the grain of wheat, resulting in even more of an association between the wheat grain and feelings of pleasure. In this way, each grain of wheat becomes more tightly associated with pleasure, making the beast increasingly likely to approach, contact, and eat the wheat. Note that the beast is saved from starving by the integrated functions of the reward system (pleasure, association, psychomotor activation). Note also that for this beast, the process of directing eating responses at food was largely automatic, conferring on this individual beast more of a chance of surviving in a patchy world of scarce food resources. The beast survives, increasing the chances of reproductive success, and transmitting this trait, the integrated reward system, to successive generations of progeny. Evolution has equipped the brain of modern beasts with the integrated reward system, deployed upon activation of NAC, to aid in survival. When we experience reward, we experience the emotion of pleasure, the association of the pleasure with stimuli present at that time, and the psychomotor activation pattern of responding.