Brain Disease of Addiction:
Scientists have long accepted that there is a biological basis for
alcohol and drug addiction, though the exact mechanisms responsible are only now being
identified. It is believed that addictive substances create dependence in the user by
changing the brain's reward functions, located in the mesolimbic
dopamine system - the part of the brain that reinforces certain
behaviors such as eating, sexual activity, exercise, and social interaction. Addictive
substances, through a variety of means and to different degrees, cause synapses of this
system to flood with excessive amounts of dopamine, creating a brief rush of euphoria;
more commonly called a "high"
Although the "high" may be short term,
it produces more and longer-lasting effects in the brain. Dopamine signals occurring
normally in the reward system, traveling form the ventral tegemental area to the nucleus
accumbens, lead to the activation of proteins designed to calm the initial reactions and
foster a continued desire to pursue the behavior responsible. Addictive substances create
a greater than normal dopamine release, and the subsequent reactions of the brain are
greatly exaggerated as well. The amygdala, hippocampus and frontal cortex associate the
use of alcohol and drugs with intense pleasure and well-being; an association that is
strengthened with each exposure, and which over time comes to dominate normal thoughts
and desires. When cravings for the drug are no longer controllable, the user is
considered addicted or "dependent".
