How Addiction Works in the Brain
It is now believed that all types of frequently abused substances set off a pleasure circuit in the brain. The same pleasure circuit works for alcohol, amphetamines, chocolate, sugar, sex, and so forth.
According to The Owner's Manual for the Brain by Dr. Pierce Howard, this pleasure circuit begins in the amygdala of the brain, then travels to the anterior cingulum, and finally on to the temporal lobes. As a whole, the pleasure circuit is called the median forebrain bundle, or in lay language, the “hedonic highway” or “pleasure pathway.”
Neurotransmitters are chemicals in the brain that transmit messages from one brain cell (neuron) to another. Dopamine, one such neurotransmitter, is the chemical most involved in the pleasure circuit and so is linked with addiction. All substances of addiction interfere with the normal reabsorption of dopamine by neurons in the brain.
By preventing this reabsorption, high levels of dopamine remain in the gaps between the neurons. Since one of the primary functions of dopamine is to give a person a sensation of pleasure, these excessive amounts of dopamine give an individual the “high” sensation. The dopamine receptor cell is the one type of cell found all along the “pleasure pathway.”
Another interesting fact in this process concerns a space between neurons in the brain called the synaptic gap. Ordinarily, neurotransmitters such as dopamine only stay in this space long enough to get picked up by receptor sites in the next neuron and then they get passed along to be used in their normal manner.
Cravings can be triggered by damage to the delivery system that moves dopamine from one brain cell (neuron) to the next. Many addicts report they often use substances not to feel “high,” but to feel “normal.” Their goal is to stop the cravings, and at this point, the survival process begins for the addict.
However, as mentioned, when absorption by the receptor sites of the next neuron is blocked, the dopamine, for example, stays in the synaptic gap and the person then experiences a “high” or pleasure effect. Many substances, such as cocaine, amphetamines, Ritalin, nicotine, and marijuana, block the absorption of dopamine by neurons in the brain.
When addictive substances are used repeatedly, it is thought to damage the dopamine delivery system, the normal movement of dopamine from one neuron to the next. Many believe that once addictions have damaged this dopamine pleasure circuit, it never completely returns to normal.