Addictive Drugs and NAC:
Drugs of abuse, such as alcohol, cocaine, and opiates, all activate the same NAC reward system that is activated by natural rewards such as food, water, and sex, but the magnitude of the activation of the NAC by abused drugs may be more than ten times greater than the effect produced by natural rewards. In this way, drugs of abuse hijack the reward system, diverting the system away from the subserving of survival, toward the subserving of addictive behavior.
The Story of Johnny Having a Drink:
Johnny is a moderate, social drinker. He enjoys having a few beers with his friends typically on the weekend. Lately, however, he has noticed that his beer intake has been gradually increasing, so that instead of having two beers at the poker game, he drinks four beers, or more. Drinking beer is pleasurable and mood-improving because the alcohol in the beer produces elevated DA activity in the NAC. In addition, the NAC has associated other stimuli present during the pleasurable experience with positive emotional feelings, so that Johnny feels good around his drinking pals. The NAC associates the people, places, and things, including sounds, like music, present while drinking beer, with the positive feelings of beer-induced euphoria. We should note that most closely associated with the DA activation of the NAC is the beer bottle. This is because the beer bottle is seen in the moments in time just before the beer is consumed. The association between the beer bottle and the activation of DA in the NAC will cause the beer bottle to become the target of the psychomotor activation syndrome. This means that Johnny will notice the beer bottle. It conspicuously stands out. Johnny will also find that he is drawn toward the beer bottle. He will reach out and taking the beer bottle in his hands, hold the beer bottle, and then drink from it. But the beer consumed due to the psychomotor activation syndrome is not the same as the beer that is consumed as a voluntary, controlled response. The psychomotor activation syndrome is a reflex coming out of the activation of the NAC. Psychomotor activation is not an intended action. Johnny did not decide to drink some more beer. Johnny is drinking beer on automatic pilot. In this way, the integrated reward system leads to beer drinking that occurs but was not intended. Obviously, beer drinking beyond what is intended is excessive beer drinking. Due to alcohol’s effects on dopamine levels in NAC, alcohol use can occur even though you do not intend to have a drink. The more you drink, the more likely psychomotor activation will produce unintended alcohol drinking.