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One human subject stimulated himself fifteen hundred times in a three-hour period, “to a point that he was experiencing an almost overwhelming euphoria and elation, and had to be disconnected despite his vigorous protests.”1
Nerve fibers from the VTA trigger dopamine release in a brain center that plays a central role in all addictions: the nucleus accumbens, or NA, located on the underside of the front of the brain.
All abusable substances raise dopamine in the NA, stimulants like cocaine most dramatically.
Indeed, the human brain’s dopamine circuits are no less important to survival than is its opioid system. If opioids help consummate our reward-seeking activities by giving us pleasure, dopamine initiates these activities in the first place. It also plays a major role in the learning of new behaviors and their incorporation into our lives.
incentive-motivation apparatus.
a cue associated with a previously pleasurable experience triggers a surge of dopamine in the NA and incites consummatory behavior.
Environmental cues associated with drug use—paraphernalia, people, places, and situations—are all powerful triggers for repeated use and for relapse, because they themselves trigger dopamine release.
it doesn’t help matters that the Portland Hotel is located within a few blocks of those unscrupulous compact disc pushers at Sikora’s, my favorite music haunt, and that I drive by there most days on my way to or from work. As I described earlier, I can feel excitement rising as I approach the store, even when I have no plan to go there, along with an urge to park the car and walk in.
Needless to say, life-essential reinforcers such as food and sex trigger VTA activation and dopamine release in the NA, since the performance of survival-related behaviors is the very purpose of the incentive-motivation system.
nerve fibers in the VTA are triggering dopamine release in the NA when a person needs to know, “Is this new whatever-it-is going to help me or hurt me? Will I like it or not?” The role of the dopamine system in novelty-seeking helps explain why some people are driven to risky behaviors such as street racing. It’s one way to experience the excitement of dopamine release.
Dopamine activity also accounts for a curious fact reported by many drug addicts: that obtaining and preparing the substance gives them a rush, quite apart from the pharmaceutical effects that follow drug injection.
Many addicts confess that they’re as afraid of giving up the activities around drug use as they are of giving up the drugs themselves.
As long as this artificial supply of dopamine receptors was available, the mice reduced their alcohol intake considerably—but they gradually became boozers again as the implanted receptors were lost to natural attrition.
chronic cocaine use reduces the number of dopamine receptors and thereby keeps driving the addict to use the drug simply to make up for the loss of dopamine activity.
research now strongly suggests that the existence of relatively few dopamine receptors to begin with may be one of the biological bases of addictive behaviors.4 When our natural incentive-motivation system is impaired, addiction is one of the likely consequences.
The dopamine system is most active during the initiation and establishment of drug intake and other addictive behaviors. It is key to the reinforcing patterns of all drugs of abuse—alcohol, stimulants, opioids, nicotine, and cannabis.
On the other hand, opioids—innate or external—are more responsible for the pleasure-reward aspects of addiction.
Opioid circuits and dopamine pathways are important components of what has been called the limbic system, or the emotional brain. The circuits of the limbic system process emotions like love, joy, pleasure, pain, anger, and fear. For all their complexities, emotions exist for a very basic purpose: to initiate and maintain activities necessary for survival.
When impaired or confused, as it often is in the complex and stressed circumstances prevailing in our “civilized” society, the emotional brain leads us to nothing but trouble. Addiction is one of its chief dysfunctions.
“Recent studies have shown that repeated drug use leads to long-lasting changes in the brain that undermine voluntary control,”
“Although initial drug experimentation and recreational use may be volitional, once addiction develops this control is markedly disrupted.”
addiction also disrupts the self-regulation circuits—which the addict needs in order to choose not to be an addict.
